As the scattering and absorption of radiation by atmospheric particles are central to Earth’s radiation balance, this session facilitates an exchange of insights between the measurement and modeling communities. Accurately quantifying these radiative effects remains a challenge. Specifically, uncertainties in morphology and the computational cost of modeling complex particles necessitate novel and efficient approaches.
The session aims to be a forum for sharing information on the state-of-the-art and emerging developments in atmospheric sensing measurements and modeling. We welcome contributions from atmospheric scientists, engineers, and industry. Topics include developments and applications of novel spectroscopic methods (such as frequency comb, cavity-enhanced, and photoacoustic spectroscopies) dedicated to measuring aerosols, isotopologues, and trace gases, as well as advances in the measurement and modeling of atmospheric particle optics. Approaches using ground and airborne platforms, simulation chambers, and new data analysis tools (including deep learning) are also encouraged.
Orals: Wed, 6 May, 14:00–18:00 | Room 1.61/62
The optical properties of atmospheric hydrometeors are a key component of forward operators used in data assimilation and model evaluation. Recent advances in microphysical modelling, such as Lagrangian super-particle models with habit prediction, enable the continuous evolution of ice particle properties and therefore require scattering databases that cover a wide range of particle morphologies.
The discrete dipole approximation (DDA) provides highly accurate scattering calculations for arbitrarily shaped ice particles but is computationally expensive, which has limited the diversity of particle shapes or environmental conditions represented in existing databases. This restricts their applicability for models with complex and evolving microphysics.
We present a new DDA-based database of ice particle optical properties at 5.6, 9.6, 35.6, and 94 GHz, designed to support habit-evolving microphysical schemes. The database follows two complementary designs. The first includes approximately 2500 ice crystals and 450 aggregates with scattering properties computed for multiple orientations, allowing a flexible treatment of particle canting. The second design sacrifices orientation diversity to maximize particle variability, comprising scattering properties for about 10 million aggregates and 1 million ice crystals calculated for a single orientation.
This newly developed database allows to forward simulate the output of the Lagrangian Monte-Carlo particle model McSnow, in which a habit prediction for ice crystals and aggregates has recently been implemented. The simulations reproduce characteristic radar signatures in the ice phase and thus allow to study the ice microphysical processes responsible for these radar signatures.
How to cite: von Terzi, L., Kneifel, S., Ori, D., Jakub, F., Seifert, A., and Siewert, C.: A Microwave Scattering Database of Oriented Ice and Snow Particles: Supporting Habit-Dependent Growth Models and Radar Applications, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18008, https://doi.org/10.5194/egusphere-egu26-18008, 2026.
Accurately representing the optical properties of atmospheric ice particles remains a major challenge for climate simulations and remote sensing. A key limitation is the lack of experimental benchmark data that directly link ice crystal microphysics to angular light scattering, particularly at the level of individual atmospheric particles.
In this contribution I will give an overview of recent advances enabled by the Particle Habit Imaging and Polar Scattering (PHIPS) instrument. PHIPS provides unique aircraft-based, in situ measurements combining high-resolution stereo-microscopic imaging with simultaneous angular light-scattering observations of the same ice crystal. This capability enables a consistent investigation of scattering behavior from single, oriented particles to habit-averaged populations and cloud-averaged ensembles.
Single-particle analyses show that even ice crystals appearing pristine in microscopic images require a finite degree of mesoscopic surface roughness to reproduce their measured angular scattering functions. This demonstrates that sub-wavelength-scale surface irregularities fundamentally control the angular scattering properties of individual atmospheric ice crystals.
For habit-averaged crystal populations, PHIPS observations of atmospheric bullet rosette crystals reveal asymmetry parameters (g) that are substantially lower than predicted by ray-tracing models assuming idealized geometries, implying a significantly enhanced shortwave reflectivity of cirrus clouds. At the cloud-averaged scale, PHIPS measurements from mid-latitude and Arctic cirrus consistently yield low g values of about 0.74, with a systematic decrease toward larger particles.
Together, these results show that ice crystal complexity across scales must be explicitly represented in optical models and establish PHIPS data as a critical benchmark for advancing such models.
How to cite: Schnaiter, F. M.: An observational benchmark of ice crystal light scattering: insights from a decade of airborne in situ measurements with the PHIPS instrument, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20374, https://doi.org/10.5194/egusphere-egu26-20374, 2026.
We develop and assess a Lattice Boltzmann Method (LBM) framework for modelling electromagnetic wave scattering by atmospheric particles, with a focus on complex and aspherical geometries relevant to climate science and optical remote sensing. In this formulation, mesoscopic distribution functions for the electric and magnetic fields evolve on a discrete lattice, from which the macroscopic Maxwell equations emerge through a Chapman–Enskog expansion. The method inherently accommodates irregular boundaries, making it well-suited for non-spherical particle shapes. Scattering computations are performed for circular and hexagonal cylinders, as well as spherical scatterers. The results are benchmarked against analytical and semi-analytical solutions, such as classical Mie theory and the Discretised Mie Formalism. Across the Rayleigh, Mie, and geometric-optics regimes, the LBM accurately captures key scattering features, including edge diffraction, interference structures, and far-field distributions, while retaining second-order accuracy in space and time. With its entirely local update rules, strong parallel scalability, and flexibility in representing complex geometries, the LBM provides a promising framework for simulating light scattering by atmospheric particles such as ice crystals and aerosol aggregates. These results highlight its potential to complement existing scattering models and support improved optical parameterizations for weather, climate, and remote sensing applications.
How to cite: Khan, M. M., Thampi, S. P., and Roy, A.: Lattice Boltzmann Method for Electromagnetic Scattering by Complex Atmospheric Particles, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-923, https://doi.org/10.5194/egusphere-egu26-923, 2026.
Due to their high versatility, spheroids are commonly employed to model optical properties of mineral dust. However, they are usually considered to be of limited use when studying multispectral depolarisation ratios of mineral dust. An earlier study, in which a spheroidal model was fitted against measurements of the linear depolarisation ratio in near-backscattering direction from 131 dust samples [1], served as a starting point for single scattering calculations using the T-matrix method.
Calculations were performed for different log-normal size distributions at wavelengths of 355nm, 532nm, 1064nm, and 910.6nm. The former three wavelengths are commonly used in lidar remote sensing, while the fourth wavelengths is used in depolarisation-capable ceilometers. In addition, aspect ratios between 0.5 and 2.0 with linearly equidistant steps of 0.01 were considered. Multiple aspect ratios were identified, which yield the linear depolarisation ratios in backscattering direction at 355nm, 532nm, 1064nm consistent with reported lidar field observations and laboratory experiments.
When additionally considering ceilometer observations of dust plumes over the tropical Atlantic during February and March 2025 at a wavelength of 910.6nm, the number of aspect ratios yielding observationally consistent depolarisation ratios is reduced. These aspect ratios encompass both prolate and oblate spheroids. One of these aspects ratios (ε=1.46) corresponds to the median aspect ratio obtained from earlier electron microscopy analysis of freshly emitted dust in the Moroccan Sahara [2].
[1] M. Kahnert, F. Kanngießer, E. Järvinen, and M. Schnaiter, “Aerosol-optics model for the backscatter depolarisation ratio of mineral dust particles,” J. Quant. Spectrosc. Radiat. Transf. 254, 107177 (2020).
[2] A. Panta, K. Kandler, A. Alastuey, C. González-Flórez, A. González-Romero, M. Klose, X. Querol, C. Reche, J. Yus-Díez, and C. Pérez García-Pando, “Insights into the single-particle composition, size, mixing state, and aspect ratio of freshly emitted mineral dust from field measurements in the Moroccan Sahara using electron microscopy,” Atmos. Chem. Phys. 23, 3861–3885 (2023).
How to cite: Kanngiesser, F.: Calculating observationally consistent multi-spectral dust depolarisation ratios with spheroids, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3522, https://doi.org/10.5194/egusphere-egu26-3522, 2026.
Mineral dust is the most abundant aerosol in the atmosphere and hence has a strong impact on atmospheric processes (i.e., aerosol-cloud and aerosol-radiation interactions). To learn more about the microphysical properties of mineral dust, remote sensing techniques using ground- and spaceborne lidars have been developed. These retrievals typically depend on fundamental assumptions about the shape and composition of the mineral dust particles. Since mineral dust particles are exclusively non-spherical, it is not appropriate to use spherical particles for the optical calculations. In the past, spheroids (Dubovik et al., 2006) and, more recently, the irregular hexahedra ensemble model (Saito et al., 2021) have been used as dust shape models. However, these models still neglect small-scale surface irregularity or surface roughness, an important morphological characteristic of mineral dust, which may lead to biases in retrieved microphysical properties.
We present preliminary results of a new dust morphological model, a roughened irregular hexahedra model. By using the random Fourier method, we add geometric surface roughness to the irregular hexahedra model particles, creating a more realistic-looking particle morphology than previously used models. We study the sensitivity of the optical properties to the degree of surface roughness. In particular, we focus on the impact on the integrated properties (i.e., single scattering albedo and asymmetry parameter), and the backscattering properties (i.e., the extinction-to-backscatter ratio and depolarization ratio), which are highly relevant for active remote sensing, and integrated (single scattering albedo and asymmetry parameter) properties. The new model shows promising results for better explaining lidar measurements. Furthermore, we present our plans for a flexible scattering database for use in remote sensing, radiative transfer, etc., openly available to the community.
O. Dubovik et al., “Application of spheroid models to account for aerosol particle nonsphericity in remote sensing of desert dust,” Journal of Geophysical Research: Atmospheres,2006
M. Saito, et al., “A Comprehensive Database of the Optical Properties of Irregular Aerosol Particles for Radiative Transfer Simulations,”2021
How to cite: Oppermann, T., Saito, M., and Haarig, M.: Sensitivities of Mineral Dust Optical Properties to Surface Roughness, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9255, https://doi.org/10.5194/egusphere-egu26-9255, 2026.
The miniaturization of sensitive as well as selective laser-based gas detectors is of big request among different fields of activity due to specific characteristics such as a fast sensor response or simply a small footprint. However, it still remains challenging. While methods based on direct absorption spectroscopy show a limited potential for miniaturization due to their dependence of sensitivity on the optical path length according to the Lambert-Beer law, indirect spectroscopic techniques of photothermal nature inherently exhibit high miniaturization potential, even down to integration onto a chip.
The Interferometric Cavity-Assisted Photothermal Spectroscopy (ICAPS) method has been proven highly suitable for sensitive and compact gas detection by application of a Fabry-Perot interferometer (FPI) as transducer for photothermal spectroscopy. The implementation of a balanced detection scheme to our developed system is a key improvement, which enhances the sensor’s performance by efficient cancellation of noise.
Within the presentation, recent results of a setup employing individual interferometers will be shown. Here, balanced-detection was realized by using two identical cavities having a path length of 1 mm and a total sample gas volume of a few mm³. The system uses an all fiber-coupled probe laser configuration, which detected the reflectance of the interferometers, enabling sensor operation close to the fundamental limit of shot noise. The metrological figures of merit were investigated by detection of different trace gases such as SO2, CO and NO using QCLs as powerful mid-infrared excitation sources. The induced refractive index changes were monitored by a near-infrared probe laser. For the targeted molecules a minimum detection limit down to the sub-ppbv level was achieved with a 1s integration time, corresponding to a normalized noise equivalent absorption of the order of 10−9 cm−1 W Hz−1/2.
Additionally, latest progress regarding sensor miniaturization will be discussed. FPIs made solely from single-crystalline silicon with Bragg mirrors consisting of silicon-air dielectric multilayers [2] were designed and fabricated. The FPIs allow easy coupling of the near-infrared beam by optical fibers positioned in the chip along aligned grooves. First demonstration of ICAPS gas sensing employing a silicon FPI will be shown.
References
[1] J. P. Waclawek, H. Moser, and B. Lendl, “Balanced-detection interferometric cavity-assisted photothermal spectroscopy employing an all-fiber-coupled probe laser configuration,” Opt. Express 29, 7794-7808 (2021).
[2] M. Malak Karam, et al., “Micromachined Fabry–Perot resonator combining submillimeter cavity length and high quality factor”, Appl. Phys. Lett., 21 (98), id. 211113 (2011).
How to cite: Waclawek, J. P., Moser, H., and Lendl, B.: Compact Trace Gas Sensing by Balanced-Detection Interferometric Cavity-Assisted Photothermal Spectroscopy (ICAPS), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22495, https://doi.org/10.5194/egusphere-egu26-22495, 2026.
Greenhouse gases (GHGs) emissions from human activities provided the majority contribution towards global warming, which make our world is now warming faster than at any point in recorded history. High precision measurement of GHGs are very important for monitoring or scientific studies. Here, laser absorption spectroscopy, especially, high sensitivity optical cavity enhanced absorption spectroscopy techniques and instruments for measurement of greenhouse gases were developed. High precision of 0.25 ppm and 2ppb was achieved for measurement of CO2 and CH4, by employing off-axis integrated cavity output spectroscopy technique. Using multi-pass cell based mid-infrared absorption spectroscopy, a precision of 0.1 ppb was achieved for N2O measurement. Results of the developed instruments for applications in GHGs measurements will be presented.
How to cite: Liu, K., Chen, W., and Gao, X.: Cavity enhanced absorption spectroscopy for high precision measurement of greenhouse gases, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4560, https://doi.org/10.5194/egusphere-egu26-4560, 2026.
The monitoring of the Earth’s atmospheric composition requires very sensitive satellite-based measurements that detect the thermal radiation emitted in the millimeter-wave and sub-THz spectral region by the constituent gas molecules. For example, much-needed vertically-resolved global ozone profile observations covering both day and night conditions are currently being made by instruments such as the Microwave Limb Sounder on board the EOS-Aura satellite. Traditionally, such radiometers have a large form factor, high power requirements, require advanced electronics and often have a cooled front-end resulting in high mission costs.
Here we present early results from a novel idea to circumvent the cryogenic requirement, thereby decreasing the payload size, weight, and power (SWaP) requirements and making the radiometers suitable for deployment as passive limb sounders on CubeSats.
Our design converts the atmospheric thermal emission (at 100 GHz – 1 THz) into the optical domain (e.g., infrared - approximately 200 THz). The up-converted signals can be referenced and radiometrically interpreted to measure the temperature of the emitting area.
Having these atmospheric signatures in the infrared domain enables the use of ultra-low-noise optical detection techniques (such as filtered single photon counters or optical heterodyning with a quiet reference laser) that are not available at microwave frequencies. Optical detection methods avoid the fundamental added noise associated with phase-insensitive microwave amplification, with noise instead dominated by optical shot noise and conversion efficiency. On top of that, most of the required components can be integrated into a compact modular device which reduces the footprint dramatically and will allow the device to be packed onto a cost-efficient CubeSat platform.
In order to convert electromagnetic radiation from one spectral region to another, we use a second-order optical nonlinear process. To achieve sufficient efficiency of photon up-conversion, high-quality crystalline microresonators are found to be an ideal system that is consistent with the small footprint we aim for. These electro-optic upconverters can be designed to target the specific emission frequencies of molecules in the atmosphere and detect their weak microwave signatures at ambient temperature with a sensitivity projected to be comparable to direct microwave receivers. The initial results presented here are focused frequency ranges that can be used for detection of ozone, as recent studies indicate that it is more important than ever to monitor the recovery of the ozone layer, but the same principle could later be expanded to the detection of other atmospheric species.
How to cite: Sedlmeir, F., Pollock, R., Pavri, B., Kessenich, H., Seppälä, A., Schwefel, H. G. L., and Suresh, M.: Millimeter-Wave Atmospheric Radiometry via Nonlinear Optical Upconversion, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16125, https://doi.org/10.5194/egusphere-egu26-16125, 2026.
Accurate and traceable observation of atmospheric ozone is a fundamental requirement for reliable analyses of climate evolution, air quality, and ultraviolet radiation exposure, as ozone simultaneously limits biologically harmful UV radiation and contributes to radiative forcing. Detecting and interpreting long-term ozone variability and trends requires spectroscopic inputs with high accuracy. However, ozone absorption cross sections in the UV Huggins bands (310–360 nm), used by ground-based lidars, Brewer and Dobson spectrometers, and UV-visible satellite instruments, remain a major source of uncertainty. It has been established that recommended and widely used datasets in this spectral region exhibit uncertainties exceeding 1 % at room temperature and rising above 3 % at low stratospheric temperatures. These inconsistencies introduce systematic biases when measurements from multiple platforms are combined. To address this limitation, a dedicated laser-based experimental approach was developed to determine ozone absorption cross sections with high spectral resolution and accurate frequency control across a significant part of the Huggins bands. Because continuous-wave UV laser sources are not commercially available in this wavelength range, ultraviolet radiation was produced through frequency doubling of tunable visible lasers derived from fiber-based infrared systems. These lasers were specifically designed and built for this experiment, providing narrow linewidths, stable tuning, and performance tailored to high-precision ozone spectroscopy. Two complementary laser systems were implemented: one operating between 307.8 and 308.2 nm, targeting wavelengths relevant for stratospheric lidar applications, and a second system covering 308–318 nm to match the spectral requirements of Brewer and Dobson spectrometers as well as satellite instruments. The experimental setup includes a purpose-built absorption cell that allows measurements over a controlled temperature range from −80 °C to +30 °C, thereby reproducing atmospheric conditions encountered from the ground to the lower stratosphere. Ozone used in the experiments is generated on site and has a purity of 99.8 %. In connection with simultaneous ozone measurements at 254 nm, this ensures traceability to the photometric ozone standard and minimizes contamination effects. The use of custom high-resolution laser sources and a temperature-controlled measurement cell significantly reduces biases associated with conventional broadband UV spectroscopy. The developed methodology provides a robust framework for improving existing ozone absorption datasets and for harmonizing measurements across different observing platforms.
How to cite: Mahob, C., Ancellet, G., Bazureau, A., Debacker, M.-R., Elandaloussi, H., Godin-beekmann, S., Gu, R., Hilico, A., Jeseck, P., Marie-jeanne, P., Pazmiño, A., Rouille, C., Santarelli, G., Zanon, T., and Janssen, C.: Custom High-Resolution UV Laser Systems for new Accurate Ozone Absorption Cross Section measurements in the Huggins bands, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18282, https://doi.org/10.5194/egusphere-egu26-18282, 2026.
Gaseous nitrous acid (HONO) is an important source of hydroxyl radicals (OH) in the atmosphere, significantly influencing atmospheric oxidation capacity and the formation of secondary pollution. However, its extremely low environmental concentration, combined with considerable spatial and temporal variations, presents challenges for high-precision monitoring. This study employs a quantum cascade laser (QCL) with a central wavelength of 1280 cm-1, utilizing highly sensitive Tunable Laser Absorption Spectroscopy (TLAS) and Cavity Ring-Down Spectroscopy (CRDS) techniques to measure HONO. Initially, high-precision calibration measurements were conducted on the HONO absorption lines within this wavelength range. Subsequently, the acquired spectral line data were used to carry out highly sensitive measurements and noise reduction on the HONO spectral lines, employing CRDS technology alongside time convolutional neural networks. The findings of this study indicate that mid-infrared spectroscopy, in combination with deep learning analysis, provides an efficient and reliable new technological approach for real-time, high-precision monitoring of atmospheric trace HONO.
How to cite: Cui, X., Yin, S., Zhu, Q., Fang, Y., Wang, J., and Li, D.: Highly sensitive detection of atmospheric HONO using mid-infrared spectroscopy combined with deep learning, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3214, https://doi.org/10.5194/egusphere-egu26-3214, 2026.
Mid-infrared time-resolved spectroscopy with high sensitivity and spectral resolution offers powerful opportunities to investigate transient light–matter interactions, as well as probing short-lived free radicals and unstable reaction intermediates. Dual-comb spectroscopy, as an emerging Fourier transform spectroscopic technique based on two frequency combs with slightly different repetition rates, enables rapid, broadband, and high-resolution spectral measurements. Here, a new approach to time-resolved infrared laser spectroscopy based on dual-comb interferometry will be presented. In addition to introducing the unique capabilities of time-resolved dual-comb spectrometers [1–3], applications including precision measurements of line strengths of important atmospheric radicals, as well as accurate determinations of reaction rate coefficients for key atmospheric chemical reactions, will be reported [4–7].
[1] P.-L. Luo and E.-C. Horng, Commun. Chem., 3, 95 (2020). [2] P-L. Luo, Opt. Lett., 45, 6791 (2020). [3] P.-L. Luo and I-Y. Chen, Anal. Chem. 94, 5752 (2022). [4] C.-W. Chang, I-Y. Chen, C. Fittschen, and P.-L. Luo, J. Chem. Phys., 159, 184203 (2023). [5] I-Y. Chen, C.-W. Chang, C. Fittschen, and P.-L. Luo, J. Phys. Chem. Lett., 15, 3733 (2024). [6] C.-W. Chang, I-Y. Chen, and P.-L. Luo, J. Chem. Phys., 162, 034302 (2025). [7] I-Y. Chen, C.-W. Chang, Q.-R. Huang, J.-L. Kuo, and P.-L. Luo, Phys. Chem. Chem. Phys., 27, 16123 (2025).
How to cite: Luo, P.-L.: Applications of Time-Resolved Mid-Infrared Dual-Comb Spectroscopy in Chemical Physics and Atmospheric Chemistry, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3964, https://doi.org/10.5194/egusphere-egu26-3964, 2026.
We report, to the best of our knowledge, the first field-deployable ultraviolet (UV) dual-comb spectrometer (DCS) for environmental sensing of formaldehyde. By combining broadband UV spectroscopy with sub-second temporal resolution the instrument enables fast, sensitive, and species-selective measurements of trace gas concentrations. Formaldehyde is a significant atmospheric pollutant and photochemical precursor with adverse effects on human and environmental health.
Current observational capabilities are limited by a gap between satellite-based remote sensing, which provides large-scale coverage, but coarse spatial and temporal resolution, and stationary in-situ instruments, which offer high sensitivity but represent only localized sampling volumes with often a bad selectivity. The presented system addresses this gap by enabling measurements with spatial resolutions ranging from hundreds of meters to kilometres, making it well suited for mobile and regional-scale atmospheric studies. Preliminary tests resulted in a resolution of 35 ppb formaldehyde for a total pathlength of 1 km and a measurement time of 1s with potential improvement in sensitivity by one order of magnitude.
Leveraging recent advances in dual-comb laser technology, we developed a compact and mechanically robust spectrometer that generates coherent radiation in the ultraviolet spectral region around 350 nm without any moving optical components. This design ensures high stability and reliability under field conditions and makes the system particularly suitable for mobile deployments. The use of DCS allows for the integration of many measurements, each fast enough to be unimpeded by atmospheric turbulences, via coherent averaging.
These characteristics make UV dual-comb spectrometers especially promising for environmental monitoring and remote sensing applications. The demonstrated system operational in a car represents a significant step toward next-generation atmospheric sensing platforms capable of bridging observational scales and extending DCS environmental sensing to the ultraviolet.
How to cite: Gruber, C., Ehl, E., Di Vora, R., Speletz, A., Pal, M., and Bernhardt, B.: Field-Deployable Ultraviolet Dual-Comb Spectrometer for Mobile Formaldehyde Sensing, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18417, https://doi.org/10.5194/egusphere-egu26-18417, 2026.
Measurements of greenhouse gases (GHGs) in the atmospheric column are crucial because column-averaged mixing ratio integrate concentrations over the full vertical extent of the atmosphere, making them far less sensitive to local mixing and transport errors than surface in situ measurements. Water vapour (H₂O) is a very highly variable and most common greenhouse gas in the Earth’s atmosphere. Column measurements of water vapour provide robust information on the total atmospheric moisture content, which is essential for the study of Earth’s radiation budget. Complementing this, vertical concentration profiles remain essential for investigating regional water cycle and its role in climate variability and environmental change. Together, column measurements and vertical profiles provide a more complete and reliable understanding of atmospheric water vapour distribution and its relevance to climate processes [1].
A portable, fully fiber-coupled laser heterodyne radiometer (LHR) has been developed at the Laboratoire de Physico-Chimie de l’Atmosphère (LPCA) for ground-based remote sensing of atmospheric carbon dioxide (CO₂) [2] and water vapour (H₂O). The system employs a wide-band, tunable external-cavity diode laser operating in the 1520–1620 nm spectral range as the local oscillator. Field measurements were conducted during a dedicated campaign at the CNES balloon launch facility in Aire-sur-l’Adour, France, within the framework of the CNES ATMOSFER project.
This study demonstrates the capability of the LHR to sensitively retrieve vertical water vapour concentration profiles from ground-based measurements using optimal estimation method. The retrieved H₂O profiles were further validated against high-vertical-resolution in-situ balloon-borne observations, including measurements from the Pico-Light H₂O instrument and the Micro-hygrometer. In addition, a real-time intercomparison was performed using simultaneously radiosonde launches, providing an independent assessment of the temporal consistency of the LHR retrievals. Instrument sensitivity and information content were further evaluated through averaging kernel analysis, and the data inversion was carried out using the ARAHMIS (Atmospheric Radiation Algorithm for High-Spectral Resolution Measurements from Infrared Spectrometers) radiative transfer model [3]. Furthermore, the diurnal variation of water vapour concentration was investigated using successive LHR measurements, demonstrating the instrument’s capability for continuous daytime monitoring.
Acknowledgments
This work is supported by the CNES ATMOSFER project and partially supported by the French national research agency (ANR) under the Labex CaPPA (ANR-10-LABX-005) contract, the EU H2020-ATMOS project (Marie SkANR-10-L-Curie grant agreement No 872081), and the regional CPER ECRIN program.
Reference
[1] M. Held, B. J. Soden, “Water vapor feedback and global warming”, Annual Review of Energy and the Environment 25 (2000) 441–475.
[2] J. Wang, T. Tu, F. Zhang, F. Shen, J. Xu, Z. Cao, X. Gao, S. Plus, and W. Chen, "An external-cavity diode laser-based near-infrared broadband laser heterodyne radiometer for remote sensing of atmospheric CO2", Optics Express 31 (2023) 9251-9263.
[3] M. T. El Kattar, T. Wei, A. Saxena, H. Herbin, W. Chen, “Potential CO₂ measurement capabilities of a transportable Near Infrared Laser Heterodyne Radiometer (LHR)”, Atmospheric Measurement Techniques 18 (2025) 4515-4526.
How to cite: Saxena, A., El Kattar, M. T., Wei, T., Ghysels-Dubois, M., Durry, G., Amarouche, N., Chartier, M., Krysztofiak, G., Samake, J.-C., Chevrier, S., Lecas, T., Paquet, C., Herbin, H., and Chen, W.: Remote sensing of water vapour in the atmospheric column using laser heterodyne radiometer, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18738, https://doi.org/10.5194/egusphere-egu26-18738, 2026.
Carbon dioxide and methane are key greenhouse gases emitted by human activities, accounting for ~75% and ~18% of total greenhouse gases emissions at the global scale. However, current knowledge about the sources and sinks of both gases is still insufficient for reliable climate predictions. Space-based observations (such as GOSAT, OCO-2 and TANSAT), primary means for quantification of the sources and sinks on large scales, suffer from limited precision and sparse observational density. Whilst ground-based observations such as TCCON, equipped with high spectral resolution Fourier transform spectrometer (FTS, Bruker, IFS125HR), provide column-averaged abundances with high precision and accuracy, however the shortfalls (such as large dimensions and high cost of maintenance) limit further expansion of the observing network. Over the last decade, COCCON, which equipped with middle spectral resolution portable FTS (Bruker, EM27/SUN), has proven to be a promising complement to the ground-based observations. With the objective to develop a portable instrument maintained with high spectral resolution, a refined laser heterodyne radiometer (LHR) for precise remote sensing of greenhouse gases will be presented.
How to cite: wang, G., chen, Z., xiong, H., fu, N., liu, K., and gao, X.: Refined laser heterodyne spectroscopy technology for precise greenhouse gas monitoring, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2225, https://doi.org/10.5194/egusphere-egu26-2225, 2026.
While optical techniques for fire detection have evolved from simple visual observation to more advanced hyperspectral imaging systems, there remains a need for compact, selective and field-deployable tools capable of quantifying and characterizing both intensity and spectral signatures of flames. This work introduces a novel approach to Fire Optical Measurements (FOM) that leverages spectral emissions from potassium, a key tracer of flaming biomass combustion. We describe the development of a sensor platform operating in the near-infrared region to isolate potassium emission features (K-FOM) in both and simple “field-scale” demonstrations. By targeting radiative emission signatures specific to biomass burning, the system offers a promising method to differentiate wildfires from fossil fuel combustion, as well as to differentiate lower-temperature smoldering fires from intense crown fires.
The K-FOM system builds on our prior experience in developing Laser Heterodyne Radiometry (LHR) sensors used for greenhouse gas measurements via in solar occultation, employing a similar optical design. In K-FOM, radiation from a potassium containing flame is collected (using a single-mode fiber or free-space collection optics). The collected radiation is mixed with light from a tunable diode laser operating near 770 nm. The resulting radio frequency signal from the combined beam carries both broadband contributions from flame particulate and the sharp emission lines from excited potassium atoms.
This presentation focuses on testing this technique in a model, laboratory system. Conserved scalars are widely used in wildfire modeling to simplify complex thermochemistry by linking species concentrations or formation rates for species to a single, passively-advected quantity through a look-up library. Mixture fraction, which represents the local proportion of fuel mass (from the unburnt cold or gaseous fuel) relative to the total mixture mass, is a key conserved scalar used in wildfire models such as the NIST Fire Dynamics Simulator. To explore the validity of this approach to potassium fire chemistry, potassium chloride solutions are nebulized into a well-characterized laboratory flame system. By mapping ground state potassium mixture fraction, using Tunable Diode Laser Absorption Spectroscopy (TDLAS), the spatial profile of potassium emission, and data from prior structural measurements and computations in this system, we refine detailed mechanisms for potassium fire chemistry and test mechanism reduction strategies.
How to cite: Miller, J. H. and McCaughey, E.: Potassium Radiative Emissions for Wildfire Detection: Developing a Path Toward Laser Heterodyne Radiometry, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21687, https://doi.org/10.5194/egusphere-egu26-21687, 2026.
Accurate measurements of water vapor (H2O) in the upper troposphere-lower stratosphere (UTLS, ~8-25 km altitude) are still very challenging, due to the low abundance of H2O in this region (~5 ppm). The standard method for balloon-borne measurements of UTLS H2O in global monitoring networks (e.g., GRUAN, GCOS reference upper air network) is chilled-mirror hygrometry. However, this technique is currently undergoing a major reconception, with the introduction of Peltier-based instruments as well as alternative cooling agents to the phasing-out fluoroform (HFC-23). Therefore, alternative, high-accuracy methods for in-situ measurements of UTLS H2O are required.
To this aim, we developed ALBATROSS, a lightweight (< 3.5 kg) laser absorption spectrometer for balloon-borne measurements of UTLS H2O [1]. ALBATROSS is based on a continuous-wave (cw) distributed feedback quantum cascade laser (DFB-QCL) emitting at 6.014 μm, and a monolithic segmented circular multipass cell with an optical path length of 6 m and a cell diameter of 10.8 cm. The multipass cell is highly resistant to thermal and mechanical stress, and can be operated either in a closed-path (laboratory) or an open-path (flight) configuration.
The performance of the spectrometer at UTLS-relevant conditions was assessed by a series of laboratory-based validation experiements. These measurements require the generation of reference gases with H2O amount fractions in the low-ppm range (< 5 ppm), and their quantification at low pressures (< 100 mbar). At such conditions, artifacts due to the strong surface adsorption/desorption properties of H2O become critical. These "memory" effects must be minimized by a careful design of the gas handling system and of the experimental procedure. At the same time, to achieve the required accuracy of ~1-2 % (i.e., 50-100 ppb), high-order line shape models, beyond the standard Voigt profile, must be considered for the spectroscopic retrieval.
In this presentation, we focus on the technical challenges and the results achieved in two distinct activities performed with ALBATROSS: an SI-traceable validation, using reference gases generated by a dynamic-gravimetric permeation method [2], and the AquaVIT-4 intercomparison of atmospheric hygrometers, held at the AIDA cloud simulation chamber in Karlsruhe, Germany [3]. Particularly, we highlight the best practices to address surface effects and other artifacts related to the gas handling system, as well as the importance of using an advanced line shape model (namely, the quadratic speed-dependent Voigt profile, qSDVP), and how to empirically obtain the necessary parameters not contained in the HITRAN database. This provides a general blueprint for the validation of a laser spectrometer dealing with a highly adsorbing gas at very low concentrations and pressures, such as H2O at UTLS-relevant conditions, in a laboratory setting.
The instrument is currently deployed in a series of atmospheric test flights within the Swiss H2O-Hub GCOS-project. Overall, the results demonstrate the exceptional potential of mid-IR laser absorption spectroscopy as a new reference method for in situ measurements of UTLS H2O.
[1] Graf et al., Atmos. Meas. Tech., 14, 1365–1378, 2021.
[2] Brunamonti et al., Atmos. Meas. Tech., 16, 4391–4407, 2023.
[3] Brunamonti et al., Atmos. Meas. Tech., 18, 5321–5348, 2025.
How to cite: Brunamonti, S., Scheidegger, P., Bühlmann, T., Pascale, C., Ghysels, M., Saathoff, H., Emmenegger, L., and Tuzson, B.: Laboratory validation of a compact laser spectrometer for trace-level water vapor measurements , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9902, https://doi.org/10.5194/egusphere-egu26-9902, 2026.
We present two infrared laser spectroscopic instrument developments that illustrate how optimized measurements of H₂O enable advanced atmospheric sensing across very different operating regimes. In both cases, instrument performance is driven by careful selection of absorption lines, infrared optical design, and measurement strategies tailored to the specific application.
The first instrument is an airborne water vapor probe designed for the low-H₂O regime relevant to persistent aviation contrail cirrus. The second application employs a more sensitive mid-infrared measurement scheme, coupled to a novel sampling manifold, to measure molecular hydrogen - after catalytic conversion to H₂O - with high speed and sensitivity. Both instruments are based on tunable infrared laser direct absorption spectroscopy (TILDAS), scanning isolated H₂O absorption lines near 7205 cm⁻¹ (1.39 µm) and 1558 cm⁻¹ (6.4 µm), respectively.
This presentation will discuss the design details of these two very different instruments, as well as the application-driven requirements that informed their hardware architectures. A comprehensive set of comparison and validation results will be presented for the system developed for contrail avoidance. For the second application, hydrogen spectrometer performance and a range of deployment scenarios will be discussed, including the novel CLAIR-H₂ system for localization and quantification of hydrogen emissions using tracer release and atmospheric inversion.
Together, these examples demonstrate the flexibility of infrared laser spectroscopic instrumentation for enabling both aviation-relevant water vapor measurements and emerging atmospheric hydrogen observations.
How to cite: Herndon, S., Lunny, E., Dyroff, C., Yacovitch, T., Daube, C., Shorter, J., Wehr, R., Budney, J., Roscioli, R., and Nelson, D.: Water as a Window: Application-Driven Design of Infrared Laser Spectrometers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15145, https://doi.org/10.5194/egusphere-egu26-15145, 2026.
Ammonia (NH₃) is the most abundant alkaline gas in the atmosphere and plays a significant role in secondary aerosol formation and nitrogen cycling, influencing regional air quality and ecosystem nitrogen deposition. Agricultural activities are the dominant sources of atmospheric NH₃. However, accurate quantification of NH₃ emissions from animal enclosures remains challenging owing to the high humidity, elevated particulate loading, and wide range of NH₃ concentrations in these settings.
In this study, we present an open-path deep-ultraviolet optical absorption spectroscopy system for in situ NH₃ measurements. The instrument measures absorption spectra from 199 to 213 nm, a region in which NH₃ exhibits intense and highly structured absorption features that enable selective and sensitive detection. The entire system is powered by a portable power bank bundle and can operate continuously for over 6 hours. Laboratory characterization experiments demonstrate a detection limit of 74 ppb at a 1 s integration time with an optical path length of 50 cm. Chamber experiments show that the instrument has an excellent dynamic range, exhibiting a robust and linear response to NH₃ from 0.1 to 100 ppm. We demonstrate the application of an early-prototype to monitoring and mapping NH3 in and around animal enclosures. The technique offers new opportunities for improving NH₃ monitoring in animal housing and supports the development of mitigation strategies for agricultural air quality management.
How to cite: Wang, M. and Venables, D.: Open-path deep-ultraviolet absorption spectroscopy for ammonia measurements in animal enclosures, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7990, https://doi.org/10.5194/egusphere-egu26-7990, 2026.
Nitrogen oxides (NOx) including nitric oxide (NO) and nitrogen dioxide (NO2), are significant reactive nitrogen compounds in the tropospheric atmosphere. The circulation of NOx and free radicals are coupled and interacted with each other, which has an important influence on atmospheric oxidation capacity and the formation of air pollution. Emissions from agricultural sources are the main source of atmospheric NOx. However, due to the limitations of high-precision measurement method of NOx and its flux measurement technique, the flux intensity of NOx emissions from agricultural sources and their effects on atmospheric oxidation are still unclear.
In this presentation, we will report the latest development of amplitude-modulated cavity-enhanced absorption spectroscopy (AM-CEAS) and its application to NOx flux measurement using eddy covariance (EC) method.
The new AM-CEAS based instrument was operated at 406 nm and TTL-modulated at 5 kHz, using phase-sensitive detection for ultra-sensitive absorption measurement. The detection precisions of the instrument were 78 pptv and 30 pptv, respectively, in 0.1 s and 1 s data acquisition time, for NO2 measurement. Combining with Cavity Ring-Down Spectroscopy (CRDS), the AM-CEAS method can eliminate the calibration process of mirror reflectivity, thus realizing NO2 absolute concentration measurements. Building upon single-channel system, a dual-channel NO2 detector has been developed. It utilizes ozone titration in one channel to convert NO to NO₂, allowing for NOx measurement by calculating the difference between the channels.
Using the NOx analyzer, an EC NOx flux observation system was constructed at a wheat field of Shouxian county, and was used for measuring the atmospheric NOx and its flux intensity in summer when ozone pollution is severe. The performance of the flux observation system was evaluated and the resulting NOx fluxes were also analyzed. Based on the advantages of high sensitivity, and minimal maintenance of AM-CEAS, the flux observation system demonstrated good performance, and provided the potential for investigating NOx flux using the EC method across diverse temporal scales.
How to cite: Zhou, J., Zhao, W., Ni, S., Du, Q., Zhang, W., and Chen, W.: Development of an amplitude-modulated cavity-enhanced NOx analyzer and its application for flux measurement in a wheat field, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8501, https://doi.org/10.5194/egusphere-egu26-8501, 2026.
Commercial gas sensing is traditionally performed using Fourier-transform infrared (FTIR) or non-dispersive infrared (NDIR) spectroscopy. Advances in interband cascade laser (ICL) technology now enable the development of compact, affordable, multi-gas laser spectrometers suitable for both industrial and atmospheric monitoring. In this work we present a portable mid-IR absorption spectrometer built around a compact laser module from NanoPlus that integrates three ICLs. The design supports an additional three-laser module, enabling up to six measurement channels and positioning this platform as a practical alternative to conventional instruments for a wide range of applications.
Figure 1. Custom FPGA-based hardware platform, allowing for simultaneous control of up to six laser diodes.
The instrument is fully controlled by a custom-built, FPGA-based hardware platform responsible for high-speed data acquisition and signal generation (Fig. 1). The electronics provide six high-resolution input and six output channels, all operating at clock rates of up to 50 MHz, enabling precise, low-latency control and measurement of the optical system. An additional modular analog amplifier stage provides flexible signal conditioning for optical detectors and laser drivers. The spectrometer measures 52.5 × 35 × 19.1 cm, weighs 20 kg, and consumes 63 W of electrical power with active heating. An integrated heater stabilizes the optical bench at 32 °C, improving long-term stability. The instrument achieves 1σ precision of 160 ppb for CO2 (40 s), 200 ppt for CH4 (30 s), 180 ppt for CO (60 s), 1 ppb for N2O (60 s), 2.2 ppm for H2O (30 s), and 60 ppb for CS2 (10 s). We quantify the benefits of thermal control and validate concentration retrievals against certified gas mixtures. Field tests include vehicle-mounted mobile survey, a multi-day stationary deployment, and industrial monitoring of hydrogen impurities. Across these applications, the spectrometer demonstrates reliable, calibration-free retrievals of ambient greenhouse gas concentrations at up to 10 Hz refresh rate.
Acknowledgements
This work is part of the “Hydrogen Region East Austria Goes Live (H2REAL)” project and is funded by the Austrian Climate and Energy Fund as part of the “Energy Model Region” program, which is managed by the Österreichische Forschungsförderungsgesellschaft FFG.
How to cite: Dorfer, S., Gazizov, I., and Lendl, B.: Development of a Portable Mid-IR Spectrometer for Simultaneous Measurements of Six Trace Gases in the Atmosphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10631, https://doi.org/10.5194/egusphere-egu26-10631, 2026.
A near-infrared external-cavity laser heterodyne radiometer (EC-LHR) with balanced detection was developed for remote sensing of water vapor/δD and CO2/δ13C in the atmospheric column. This tunable external cavity laser, with a center wavelength of 1.56 µm, serves as local oscillator and offers a tuning range of hundreds of wavenumbers by scanning work temperature and current. By optimizing the optical heterodyne balanced detection configuration, the EC-LHR achieved quasi-shot-noise-limited performance. High-resolution atmospheric transmission spectra of water vapor, HDO, CO₂, and ¹³CO₂ were simultaneously measured using the developed EC-LHR operating in ground-based solar occultation mode. Within the framework of the optimal estimation algorithm, three inversion strategies were employed: single peak retrieval, multiple peaks joint retrieval, and isotopic ratio-constrained retrieval. This approach allows for the determination of the column abundance and profiles of CO₂ and water vapor, as well as δD and δ13C. The reported EC-LHR has broad application potential in the fields of anthropogenic gas emission monitoring and water vapor transport research.
How to cite: Shen, F., Wang, J., Li, J., Chen, W., and Tan, T.: Development of a near-infrared external-cavity laser heterodyne radiometer with balanced detection for the measurement of atmospheric water vapor/δD and CO2/δ13C , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2182, https://doi.org/10.5194/egusphere-egu26-2182, 2026.
We present a laser heterodyne radiometer (LHR) featuring a quasi-synchronous background detection scheme for column-integrated atmospheric water vapor measurements. The proposed scheme effectively suppresses relative background drift to within 0.8%, significantly enhancing measurement stability. The instrument achieves a high spectral resolution of 0.004 cm⁻¹ with a rapid acquisition time of 25 s per heterodyne spectrum. Field experiments were conducted in August 2024 in the Ali region of the Tibetan Plateau. Continuous observations on August 14 demonstrated stable retrievals of atmospheric H₂O column concentrations with a relative uncertainty of 1.37%. Additional measurements performed on August 16 and August 21 yielded relative uncertainties of 1.16% and 2.79%, respectively, confirming the repeatability and robustness of the system under varying atmospheric conditions. Simultaneous measurements using a Fourier transform spectrometer (Bruker EM27/SUN) showed consistent temporal variability, with a correlation coefficient of 0.77. These results indicate that the developed LHR combines fast acquisition speed, high spectral resolution, and reliable precision, making it a promising instrument for long-term and stable atmospheric water vapor monitoring, particularly in remote and high-altitude regions.
How to cite: Cao, Z., Meng, Y., Huang, J., Lu, X., and Huang, Y.: A Quasi-Synchronous Background Detection Laser Heterodyne Radiometer for Atmospheric Water Vapor Measurements, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15479, https://doi.org/10.5194/egusphere-egu26-15479, 2026.
Far-infrared (FIR) radiation plays a fundamental role in regulating the Earth’s greenhouse effect, particularly in cold and dry regions where a large fraction of the outgoing longwave radiation is emitted at FIR wavelengths. Measurements across this range are limited and previous studies have found it challenging to achieve radiative closure between different instruments across the mid-far infrared. In January and February 2025, ESA funded a campaign in the Gault Nature reserve (Canada) in support of the FORUM (Far-infrared Outgoing Radiation Understanding and Monitoring) Earth explorer mission. One of the campaign aims was investigate the consistencies between atmospheric states modelled and measured at the surface. This study exploits measurements taken by the Far INfrarEd Spectrometer for Surface Emissivity (FINESSE) instrument, a ground-based Fourier transform spectrometer, which was based at Gault.
First, clear sky scenes were selected through local HALO Doppler lidar measurements and a bi-spectral method using the FINESSE radiances. The high-resolution downwelling spectra are compared to radiative transfer simulations (LBLRTM) run with atmospheric profiles from a local radiosonde (IMET4) and the 5th ECMWF atmospheric reanalysis (ERA5). These residuals were averaged over time and the different sources of uncertainty, including spectroscopic uncertainty, were combined.
Preliminary results from this study indicate that simulations driven by ERA5 profiles generally show improved agreement with the observed radiances compared to those using IMET4 radiosonde inputs. This suggests that ERA5 more accurately captures the vertical structure of temperature and humidity during the campaign period. The radiosonde was launched very close to FINESSE, however there were strong winds and the sondes tended to fly east of FINESSE. The impact of the movement on the radiance residuals has been characterised.
The largest discrepancies in both cases are seen in the 400-600 cm-1 region and in the 𝜈2CO2 band wings between around 580 - 620 cm-1 and 710-750 cm-1. These are regions which are particularly sensitive to the water vapour and temperature profiles. Within these areas, there are sections where the residuals extend beyond the estimated combined uncertainties. The radiosonde residuals in the 400-600 cm-1 region indicate a possible dry bias. We conducted Sensitivity experiments exploring how variations in humidity within different atmospheric layers influences the simulated radiances. Furthermore, the impact of recent revisions to H₂O line parameters on the radiance residuals is explored.
How to cite: Mosselmans, S., Brindley, H., Cox, C., Gryspeerdt, E., Murray, J., Panditharatne, S., Warwick, L., Huang, Y., Riot, B., and Pery, B.: Exploring Clear-Sky Longwave Radiative Closure: A downwelling case study, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20007, https://doi.org/10.5194/egusphere-egu26-20007, 2026.
Differential Optical Absorption Spectroscopy (DOAS) is a long-standing remote sensing technique used to measure many absorbing trace gases. To attain the necessary sensitivity to weak absorptions from trace gases, conventional DOAS systems normally have kilometre- long path lengths and large telescopes to maximise the collected light. Such systems are expensive and largely limited to research applications. The work describes a low – cost, long path DOAS system with a 1.5 km path length in Cork city, Ireland specifically to measure nitrogen dioxide (NO2) for air quality monitoring. The system consists of a temperature-stabilised 0.8 W blue LED (peak wavelength at 435 nm), 5 cm diameter transmitting and receiving telescopes and a compact spectrometer. A band pass filter (420 nm – 460 nm) is used to eliminate stray light. The system is much smaller than conventional DOAS configurations and is relatively straightforward to assemble. The outlook for using long path DOAS as an affordable approach to monitor the contribution to NO2 to urban air quality is discussed.
How to cite: Vikas, R., Wang, M., Dorney, C. W., and Venables, D. S.: Remote sensing of nitrogen dioxide across Cork city using a Low- Cost Long Path DOAS system, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7989, https://doi.org/10.5194/egusphere-egu26-7989, 2026.
To address the limitations of conventional off-axis cavity-enhanced absorption spectroscopy (OA-CEAS) operated in a one-way transmission configuration-such as the low utilization efficiency of the optical integrated cavity and the difficulty in achieving simultaneous multi-species detection-an OA-CEAS system with an opposite two-way coupled detection configuration is proposed in this work. Ray-tracing simulations using TracePro and optical field analysis based on MATLAB were employed to optimize and determine key system parameters, including the cavity mirror spacing, incident aperture position, incident angle, as well as the position, radius of curvature, and relative orientation of the re-injection mirror. Based on these optimizations, a high-precision OA-CEAS optical integrated cavity with an opposite two-way configuration was constructed. Furthermore, by integrating frequency-division multiplexing (FDM)–assisted wavelength modulation spectroscopy (WMS), the output beams of four tunable diode lasers with center wavelengths of 1.567 µm, 1.571 µm, 1.620 µm, and 1.653 µm were coupled into a single optical integrated cavity. Simultaneous detection of CO, CO2, C2H4, and CH4 was achieved by extracting the second-harmonic (2f) signals of the corresponding absorption transitions.
In addition, comparative analysis with the conventional one-way OA-CEAS configuration demonstrates that the concave mirror used for reflecting and focusing the detected beam can also act as a re-injection mirror, effectively promoting light re-entry into the cavity and significantly enhancing the intracavity optical power. As a result, both the signal amplitude and the signal-to-noise ratio are improved by approximately a factor of 1.5, leading to enhanced detection sensitivity. This work highlights a new strategy for simultaneous multi-species detection using multiple lasers in a single optical integrated cavity, which improves cavity utilization efficiency, reduces system cost, and broadens the application prospects of OA-CEAS for complex gas mixture sensing.
How to cite: Cai, T. and Gao, G.: Simultaneous Multi-Species Detection Based on an Opposite Two-Way Off-Axis Cavity-Enhanced Absorption Spectroscopy , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2479, https://doi.org/10.5194/egusphere-egu26-2479, 2026.
The hydroperoxyl radicals (HO2) play a crucial role in atmospheric chemistry. Direct in-situ measurement of HO2 concentration using laser spectroscopy has always been a challenge, requiring very high detection sensitivity. In this presentation, we report the development of a frequency-stabilized cavity ring-down spectrometer (FS-CRDS) for the direct measurement of HO2 concentration. The optical cavity of the spectrometer was made of perfluoroalkoxy (PFA) tube with an inner diameter of 9 mm. The distance between the two high reflectivity mirrors (double coated, with reflectivity R = 95% at λ = 632 nm and R = 99.998% at λ = 1506 nm) was about 51.4 cm, with one of the cavity mirrors mounted on a piezo-electric transducer (PZT). A stable red He-Ne laser with a frequency stability of ±2 MHz was used as the reference laser for the cavity length stabilization servo. A 1506 nm fiber laser was used as the probe laser. The probe laser beam was split into two beams: one beam was used to lock the probe laser to the stable cavity using Pound-Drever-Hall (PDH) locking method; the other beam passed sequentially through an acousto-optic modulator (AOM) and a fiber electro-optic modulator (EOM) for cavity ring down spectroscopy (CRDS) measurement. By tuning the frequency of the microwave source drive of the EOM, and using a frequency-agile, rapid scanning spectroscopy method, the laser sidebands were sequentially switched to different optical cavity models, thereby achieving rapid full-spectrum scanning. With a 1 s integration time, the spectrometer achieved a detection sensitivity of about 2.6×10-11 cm-1, which was about 12 times improved compared with normal CRDS system without electronic locking. The corresponding detection limit for HO2 radicals was about 1.2×108 molecule/cm3 (the absorption line for HO2 detection was located at 6638.207 cm-1, with a line strength of 7.09 × 10-21 cm-1/(molecule cm-2)). This work demonstrates that FS-CRDS is a feasible technique for high sensitivity direct measurement of HO2 radicals. Further improvements will be made in the future to enhance detection sensitivity.
How to cite: Zhao, W., Chen, N., Li, Y., Fang, B., Zhang, W., and Chen, W.: Development of a frequency-stabilized cavity ring-down spectrometer for direct measurement of HO2 radicals, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3058, https://doi.org/10.5194/egusphere-egu26-3058, 2026.
Primary Biological Aerosol Particles (PBAPs) are ubiquitous in Earth’s atmosphere and have been repeatedly shown to affect human health in adverse ways as allergens or disease vectors. Their role in heterogenous freezing is also attracting increasing interest and many PBAPs are regarded as Ice Nucleating Particles (INPs) This makes PBAPs a crucial factor for Earth’s Climate. These phenomena emphasise the importance of spatially resolved information on PBAP concentrations. Current instruments use UV fluorescence spectroscopy to study PBAPs in ambient air samples, however the size and weight of these instruments limit this technique to ground- or plane-based measurements, leaving a blind spot to the lower troposphere. This highlights the need for miniaturised, UAV-mountable fluorescence spectrometers that can provide spatially resolved PBAP data from low altitudes.
To address this demand, a 3D-printed fluorescence chamber was developed and successfully tested under laboratory conditions. Due to its compact, lightweight and adaptable nature, it can be operated under UAV conditions. This was then coupled with an optical particle counter and expanded to include a wide range of different on- and offline instruments, to form a modular UAV-mountable measurement system capable of monitoring fluorescence information, particle size and mass distributions and a variety of meteorological data.
This setup was successfully used during a multi-day field campaign in Steinalpl, Styria, Austria in summer 2025. During the campaign the setup was flown consistently over an area consisting of meadows and a spruce forest suffering from heavy bark beetle infestation. The novel fluorescence spectrometer proved reliable, producing data on every flight without interruption. Preliminary results show that terrain changes can clearly be observed in the fluorescence data and that it shows correlation to other instruments from the setup, which underlines the quality of the data produced and demonstrates that the developed lightweight UAV-mountable spectrometer is an important step towards online monitoring of PBAPs in the lower troposphere.
How to cite: Rupprecht, M., Wieland, F., Wlasits, P. J., Sterlich, P., Peller, G., and Grothe, H.: Development and testing of a fluorescence-based UAV-mountable sensor for PBAP monitoring in the lower troposphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5242, https://doi.org/10.5194/egusphere-egu26-5242, 2026.
Correspondence: Min Qin (mqin@aiofm.ac.cn)
Organic nitrates (ONs), including peroxy nitrates (PNs, RO2NO2) and alkyl nitrates (ANs, RONO2), are significant nitrogen-containing organic compounds in the atmosphere. ONs are primarily produced by the reaction of volatile organic compounds (VOCs) and atmospheric oxidants (OH radical, NO3 radical and O3) in the presence of nitrogen oxides (NOx = NO + NO2). The generation and removal of ONs play a critical role in atmospheric nitrogen cycling, secondary organic aerosol (SOA) formation and climate change. The thermal dissociation (TD) method is widely employed for quantifying total PNs (ΣPNs) and total ANs (ΣANs). It indirectly measures ΣPNs and ΣANs by selectively converting them into nitrogen dioxide (NO2) through TD inlets maintained at specific temperatures, followed by NO2 detection. However, the accuracy of TD method can be compromised by secondary chemical reactions between TD-generated radicals (e.g., RO2, RO) and other atmospheric components such as NOx. This study presents a dual-channel thermal dissociation-broadband cavity-enhanced absorption spectroscopy (TD-BBCEAS) system designed for the measurement of ΣPNs and ΣANs. Two TD inlets set at 180°C (decomposing ΣPNs to NO2 + RO2 radicals) and 360°C (decomposing ΣANs to NO2 + RO radicals), achieving > 99% TD efficiency while ensuring effective separation between ΣPNs and ΣANs. The NO2 was measured by BBCEAS within the 435 - 455 nm. Potential interferences were systematically evaluated through laboratory experiments and numerical simulations. To suppress interference from NO oxidation, O3 was introduced to convert all NO to NO2, enabling precise measurement of total NOx. The quantification of ΣPNs and ΣANs was then based on the differential NOₓ (ΔNOx) between specific inlets. Additionally, the addition of quartz wool enhanced the effective collision and consumption of RO2/RO radicals within the inlet, thereby preventing the recombination of TD products. Laboratory mixed-gas experiments confirmed stable ΣPNs/ΣANs responses under variable NOₓ levels, validating effective interference suppression. Field observations in Hefei showed excellent agreement (R2 = 0.92) between the sum of ΣPNs, ΣANs, and NOx measured by TD-BBCEAS and total reactive nitrogen (NOy) from a commercial analyzer, accounting for 96% of NOy. This result further validates the feasibility of measuring ΣPNs and ΣANs.
Acknowledgments: This work was supported by the National Natural Science Foundation of China (Grant No. 42175151), the National Key Research & Development Program of China (No.2022YFC3701100) and the Anhui Major Provincial Science & Technology Project (No.202203a07020003).
How to cite: Qin, M., Shao, D., Fang, W., Han, B., Xie, J., and Zhao, X.: Quantification of total peroxy nitrates (ΣPNs) and total alkyl nitrates (ΣANs) by a dual channel thermal dissociation broadband cavity-enhanced absorption spectroscopy (TD-BBCEAS), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5094, https://doi.org/10.5194/egusphere-egu26-5094, 2026.
Nitrogen dioxide (NO2) is a major air pollutant and strongly associated with vehicle emissions. At present, there are no fast and low-cost instruments suited to mobile measurements or measurements at roadside sites. In this work, we describe a low-cost Cavity-Enhanced Absorption Spectrometer (CEAS) system for portable, in-situ measurements of NO2 in urban environments. A blue LED centred at 440 nm was used as a light source with a 12 cm optical cavity, and transmitted light was detected with a silicon photomultiplier. Sensitivity to NO2 at low ppb levels (3 ppb) was achieved at the instrument time resolution of 5 s. We discuss the application of the instrument to both stationary and mobile monitoring applications and present early work towards developing a backpack-mounted instrument.
How to cite: Dorney, C. W.: Development of a portable CEAS sensor for fast, inexpensive measurements of nitrogen dioxide in urban environments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7972, https://doi.org/10.5194/egusphere-egu26-7972, 2026.
Correspondence: Jun Duan(jduan@aiofm.ac.cn) , Pinhua Xie (phxie@aiofm.ac.cn)
Broadband cavity-enhanced absorption spectroscopy (BBCEAS) is a highly sensitive in-situ optical gas detection technique. Leveraging multiple light reflections within an optical resonant cavity, this technique yields an effective absorption path length that significantly exceeds the physical length of the cavity. This enables highly sensitive detection of trace gases, even those with extremely weak absorption characteristics. The Rayleigh scattering cross section serves as the metrological foundation for achieving absolute concentration measurements in high-precision spectroscopic techniques. In this work, we attempted to measure the Rayleigh scattering cross sections of various gases in the ultraviolet-visible spectral range. First, the effective absorption path length of the BBCEAS system was precisely calibrated. By measuring the differences in Rayleigh scattering between various gases (such as argon, carbon dioxide, sulfur hexafluoride, etc.) and helium, the Rayleigh scattering cross sections of the target gases were inversely derived, yielding a high-precision experimental dataset of gas Rayleigh scattering cross sections. In addition, considering the variations in Rayleigh scattering cross sections among different gases, a method for identifying unknown gases was proposed. The extinction coefficient of an unknown gas is measured using BBCEAS and compared with databases of known Rayleigh scattering and absorption cross sections to determine its identity, and this study provides a new approach for the rapid optical measurement of gases with negligible absorption features.
Acknowledgements : This research was funded by the National Natural Science Foundation of China (No. 42175155, 42475141), the Anhui Provincial Key R&D Program, China (No. 2023t07020016), the Youth Innovation Promotion Association of Chinese Academy of Sciences (No. 2023464), and the CASHIPS Director’s Fund (BJPY2024B10).
How to cite: Fu, J., Duan, J., and Xie, P.: Measurement of Rayleigh scattering cross sections using broadband cavity-enhanced absorption spectroscopy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10558, https://doi.org/10.5194/egusphere-egu26-10558, 2026.
Path averaged measurements of greenhouse gases (GHG) on the kilometer scale can potentially improve measurement-based estimations of anthropogenic emissions. Path averages are less sensitive to local emission patterns than point-like in-situ measurements. As a result, they could provide more robust information in the face of uncertain prior emission fields, especially if these are highly structured. A typical case are urban areas, which are a major and growing contributor to anthropogenic GHG emissions, but their contribution is also subject to significant uncertainty [1].
Many different techniques are in theory available to perform these path averaged measurements. Between all of them, dual-comb spectroscopy (DCS) comes with a distinct set of features, which make it an ideal tool for the task at hand: high spectral radiance, resulting in high precision, broadband spectral coverage, allowing access to multiple species and a robust spectroscopic evaluation and an extremly high resolution, rendering the spectra basically free of any instrument line function, to name just a few. Additionally, DCS was already demonstrated to be field-deployable [2]. Finally, rapid developments on the commercial availability of DCS systems and their building blocks result in an increased accessibility to this technique, including users without a strong background in Laser Physics and metrology.
Our near-infrared dual comb spectrometer for open-path measurements of greenhouse gases over the city of Heidelberg is centered around two fully stabilized commercially available turn-key frequency combs. We present the results of the first nine months near continuous operation along a 1.55 km long path, including side-by-side measurements with an open-path Fourier transform spectroscopy (FTS) system [3]. With a xCO2 precision of 1 ppm on a one-minute timescale the DCS system proves five times more precise than the FTS, with a clear path to improvement by at least another factor of two. This puts our system at par with previous, fully home build systems of metrology expert groups [4], all achieved in less than a year after the arrival of the lasers, demonstrating the technological maturity.
References:
[1] Federal Environment Agency, "National Inventory Report for the German Greenhouse Gas Inventory 1990 – 2019" UNFCCC Submission (2021)
[2] Nathan Malarich, et al. "Evaluating CO2 and CH4 absorption models with open-path dual-comb spectroscopy at the Mauna Loa Observatory." Journal of Quantitative Spectroscopy and Radiative Transfer (2025): 109567. https://doi.org/10.1016/j.jqsrt.2025.109567
[3] Tobias D. Schmitt, et al. "An open-path observatory for greenhouse gases based on near-infrared Fourier transform spectroscopy" Atmos. Meas. Tech., 16, 6097-6110 (2023) https://doi.org/10.5194/amt-16-6097-2023
[4] Eleanor M. Waxman, et al. " Estimating vehicle carbon dioxide emissions from Boulder, Colorado" Atmos. Chem. Phys., 19, 4177–4192, (2019) https://doi.org/10.5194/acp-19-4177-2019
How to cite: Schmitt, T. D., Dubroeucq, R., Sindram, M., Pfeifer, T., Butz, A., and Oberthaler, M. K.: A dual-comb spectrometer for open-path measurements of greenhouse gases in comparison with Fourier transform spectroscopy., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9911, https://doi.org/10.5194/egusphere-egu26-9911, 2026.
Correspondence: Pinhua Xie (phxie@aiofm.ac.cn)
Atmospheric halogens, including fluorine (F), chlorine (Cl), bromine (Br), and iodine(I), significantly impact atmospheric chemistry and climate change. Especially BrO plays an important role in the processes of ozone destruction, disturbance of NOx and HOx chemistry, oxidation of dimethyl sulfide (DMS), and the deposition of elementary mercury. BrO can be measured using the Differential Optical Absorption Spectroscopy (DOAS) method owing to their structured absorption cross sections in the UV and visible parts of the spectrum. In the troposphere, BrO has been detected in polar regions, at salt lakes, in volcanic plumes, and in the marine boundary layer using optical remote sensing approaches including MAX-DOAS, LP-DOAS, and satellite observations. This study presents an in-situ measurement instrument for atmospheric BrO detection based on broadband cavity-enhanced absorption spectroscopy (BBCEAS). The instrument utilizes a 340 nm UV LED light source operating within the 333-347 nm spectral range, which encompasses three characteristic BrO absorption bands. Allan deviation analysis for BrO reveals a detection sensitivity of about 1 pptV and a custom-built BrO generation system was developed to characterize sampling losses. The system's field deployment at the salt lake successfully conducted ground-based direct observations of atmospheric reactive halogen species. This field validation demonstrates the instrument's capability for field applications in complex environmental conditions.
Acknowledgements: This research was funded by the National Natural Science Foundation of China (No. 42175155, 42475141) , the Anhui Provincial Key R&D Program, China (No. 2023t07020016), the Youth Innovation Promotion Association of Chinese Academy of Sciences (No. 2023464), and the CASHIPS Director’s Fund (BJPY2024B10).
How to cite: Duan, J., Fu, J., and Xie, P.: Development of the broadband cavity-enhanced absorption spectrometer for in situ measurements of BrO, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9699, https://doi.org/10.5194/egusphere-egu26-9699, 2026.
Nitrate contamination in water sources is a growing concern, primarily caused by agricultural runoff, animal manure, and wastewater. This pollution leads to severe environmental issues such as lake eutrophication and oceanic dead zones, impacting tourism and fisheries. It also poses significant public health risks due to elevated nitrate levels in drinking water. Stable isotopologues of N₂O (δ15N, δ18O, and δ17O) in nitrates serve as excellent tracers for distinguishing between anthropogenic sources of nitrate pollution. Understanding variations in isotopologue composition enables targeted strategies to mitigate these harmful effects[1],[2].
Conventional methods for isotopologue analysis require chemical conversion of nitrates to refined salts (KNO₃) or N₂O gas, followed by EA-IRMS or GC-IRMS measurements. These techniques are time-consuming, involve toxic chemicals, and, in the case of GC-IRMS, require cryogenic purge-and-trap steps. While IRMS remains the gold standard, its workflow is tedious and only provides limited throughput.
We present an automated, laser-based solution for simultaneous measurement of N₂O isotopologues with high precision and repeatability. The GLA451-N2OI3 spectrometer, based on ABB’s patented Off-Axis Integrated Cavity Output Spectroscopy (OA-ICOS) technology[3], achieves precisions of 0.3 ‰ (δ15N), 0.5 ‰ (δ18O), and 3 ‰ (δ17O) at 2 ppm N₂O with a 300 seconds integration time. OA-ICOS offers excellent long-term stability and a wide linear dynamic range.
A key advantage of the GLA451-N2OI3 is its compatibility with a headspace autosampler; enabling fully automated analysis of N₂O derived from nitrates at high throughput—up to 140 samples in 24 hours. The autosampler uses a 5 mL syringe for up to 15 mL injections (3 × 5 mL). Tests with 10 ppm N₂O demonstrate repeatability of 1.5 ‰ across 36 injections, further improved to <1 ‰ with drift and reference corrections[1].
In this presentation we demonstrate the simplicity, precision and accuracy of ABB’s OA-ICOS technology, offering a robust and user-friendly spectrometer to measure the triple isotopologues of nitrate. Crucially, its unique direct δ17O measurement capability provides the full triple-isotope fingerprint, including Δ17O-excess, which is critical for distinguishing atmospheric nitrate sources. Collectively, these advancements make the GLA451-N2OI3 an invaluable tool for environmental and analytical scientists, empowering high-resolution monitoring, atmospheric nitrogen research and water quality assessments with unprecedented confidence and efficiency.
References
[1] L. I. Wassenaar, , et. al, ‘Automated rapid triple-isotope (δ15N, δ18O, δ17O) analyses of nitrate by Ti(III) reduction and N2O laser spectrometry’, Isotopes Environ. Health Stud., vol. 59, no. 3, pp. 297–308, May 2023, doi: 10.1080/10256016.2023.2222222.
[2] C. W. Kreitler, ‘Determining the source of nitrate in groundwater by nitrogen isotope studies’, 1974, Accessed: Jan. 09, 2026. [Online]. Available: http://hdl.handle.net/2152/65451
[3] D. S. Baer, et. al, ‘Sensitive absorption measurements in the near-infrared region using off-axis integrated cavity output spectroscopy’, vol. 4817.
How to cite: Nataraj, A., Fortson, S., Fdil, K., and Owen, K.: High precision laser-based N2O isotopologue analyser for environmental applications. , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12180, https://doi.org/10.5194/egusphere-egu26-12180, 2026.
Tunable Diode Laser Absorption Spectroscopy (TDLAS) is a well-established technique for sensitive gas detection based on wavelength-selective absorption. In recent years, it has gained increasing relevance for long-range atmospheric measurements of greenhouse gases such as CO2. This work presents an analytical, numerical, and experimental investigation of wavelength-modulated TDLAS applied to long open-path CO2 sensing over kilometer-scale distances.
A distributed feedback diode laser is sinusoidally modulated in injection current to generate a periodic wavelength sweep across a selected CO2 absorption line. The transmitted signal, strongly attenuated after propagation over approximately 2 km, is detected and demodulated using phase-sensitive lock-in amplification to extract the first, second, and third harmonic components (1f, 2f, and 3f). This approach enables the reliable retrieval of extremely weak absorption signals under low signal-to-noise conditions. Harmonic amplitude ratios, particularly 2f/1f and 3f/1f, are analyzed as functions of the CO2 mixing ratio under controlled laboratory conditions.
To interpret the measured harmonic signals, an analytical formulation based on the Beer–Lambert law and a parameterized description of laser wavelength tuning and optical power modulation is developed, and it is compared with numerical simulations and experimental results. We demonstrate that at elevated CO2 concentrations, the commonly used 2f/1f ratio exhibits saturation, while higher-order ratios, such as 3f/1f, retain sensitivity and provide improved robustness for long-range measurements.
Furthermore, we illustrate that even small offsets between the modulation center and the absorption line center introduce systematic odd–even harmonic mixing, increase temperature sensitivity, and compromise the stability of harmonic-based retrievals. The combined analytical, numerical, and experimental analysis provides practical guidance for optimizing wavelength-modulated TDLAS systems that employ lock-in detection for long-range atmospheric CO2 monitoring.
How to cite: Assarenayati, A., Ye, S., Kotlarov, A., Wenig, M., Haisch, C., Schmitt, S., Poppe, J., Doepke, B., and Wittrock, F.: Long-range, open path CO2 measurements using tunable diode laser absorption spectroscopy: analytical, numerical, and experimental comparison, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15054, https://doi.org/10.5194/egusphere-egu26-15054, 2026.
Sodium Chloride (NaCl) is a major component of sea salt in the atmosphere. In remote marine environments, sea salt aerosol dominates the formation of clouds. Under humid conditions often present in marine environments, sea salt exhibits a spherical shape. However, as relative humidity drops below the efflorescence point (around 45% RH), it exhibits a cubic-like shape, which leads to an enhanced depolarization ratio in lidar observations (Haarig et al., 2017). This transition was simulated by Kahnert & Kanngießer (2024), who created irregularly shaped dry sea salt crystals for single scattering calculations using Discrete Dipole Approximation (DDA) and then applied a brine coating to mimic the transition to wet, spherical sea salt particles.
We want to investigate the relation between particle size and the observed particle linear depolarization ratio of crystalline salt (NaCl) particles. For this purpose, we use the Optical Lab for Lidar Applications (OLALA) established for mineral dust research at TROPOS (see EGU 2026 contribution of Semwal et al.). The scattering laboratory is focused on the exact backscattering direction (180±0.2°) required for lidar applications. The NaCl particles are generated from wet dispersion with subsequent drying. A Differential Mobility Analyzer (DMA) ensures almost mono-modal size distributions for fine mode aerosol. Currently, we investigate NaCl particles in the size range of 250 to 800 nm in diameter at a laser wavelength of 532 nm. The extension to 1064 nm and 355 nm laser wavelengths is under construction. An increase in the depolarization ratio was observed with increasing size, reaching the maximum values of 0.16±0.04 for 800 nm dry NaCl particles.
The size-resolved laboratory results are compared to model calculations with perfect cubes and stacked cubes (different realizations) using DDA. Perfect cubes lead to lower depolarization ratios than observed in the laboratory. This finding indicates that the dry NaCl particles are not perfect cubes. Additionally, we intend to apply further particle shape models such as convex polyhedra (Kanngießer & Kahnert, 2021a), Gaussian random cubes (Kahnert & Kanngießer, 2021b) or super ellipsoids (Bi et al., 2018).
At the end, a better representation of cubic sea salt in the atmosphere will be achieved by constraining the optical particle shape models with the size-resolved laboratory results.
References:
Bi, L. et al., Optical Modeling of Sea Salt Aerosols: The Effects of Nonsphericity and Inhomogeneity, JGR, Vol. 123, No. 1, p. 543-558 (2018).
Haarig, M., et al., Dry versus wet marine particle optical properties: RH dependence of depolarization ratio, backscatter, and extinction from multiwavelength lidar measurements during SALTRACE, ACP, Vol. 17, No. 23, p. 14199-14217 (2017).
Kahnert, M. and Kanngießer, F., Optical Characterization of Marine Aerosols Using a Morphologically Realistic Model with Varying Water Content: Implications for Lidar Applications and Passive Polarimetric Remote Sensing, GRL, Vol. 51, No. 5, p. e2023GL107541 (2024).
Kanngießer, Franz and Kahnert, Michael, Modeling Optical Properties of Non-Cubical Sea-Salt Particles, JGR, Vol. 126, No. 4, p. e2020JD033674 (2021a).
Kanngießer, Franz and Kahnert, Michael, Optical properties of water-coated sea salt model particles, OE, Vol. 29, No. 22, p. 34926-34950 (2021b).
How to cite: Haarig, M., Oppermann, T., Kanngießer, F., Semwal, E., Hartmann, M., Engelmann, R., Althausen, D., Wex, H., and Saito, M.: How does the size of crystalline NaCl relate to the depolarization ratio? – First laboratory results compared to model calculations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9600, https://doi.org/10.5194/egusphere-egu26-9600, 2026.
Terahertz (THz) frequency combs (THz-FCs) offer a new powerful route to high-resolution molecular spectroscopy, providing both a broad spectral coverage and inherently excellent frequency metrology and referencing. In this work, we demonstrate a THz spectroscopic system that exploits these advantages by combining a femtosecond-laser-based THz-FC with heterodyne detection coupled with a fast Fourier transform spectrometer (XFFTS) [1]. This configuration enables the rapid and simultaneous acquisition of more than 80 comb modes spanning a 7.5 GHz bandwidth. A complete spectrum can be recorded in under 12 minutes, achieving a uniform spectral resolution of 76 kHz, determined primarily by the native channel spacing of the XFFTS.
The setup addresses a fundamental challenge in THz spectroscopy, the inherent compromise between achieving high spectral resolution and maintaining large measurement bandwidth. By leveraging multiple, coherently spaced FC modes, our approach demonstrates that simultaneous multi-mode detection is a realistic and efficient solution. The current resolution and bandwidth are limited by the XFFTS baseband (0–2.5 GHz). This range can be extended by exploiting the second Nyquist band or by integrating multiple XFFTS units to increase instantaneous coverage without added acquisition time. The IF (intermediate frequency) bandwidth will ultimately be constrained by the heterodyne mixer, which has an electrical bandwidth up to 40 GHz so could allow an instantaneous spectral bandwidth of up to 80 GHz to be measured. With emerging new generation FFT spectrometers [2].
Our results highlight the significant potential of THz-FC-based spectroscopy for accelerating high-resolution molecular investigations. This approach provides the means to acquire detailed, accurate spectra at unprecedented speeds, enabling advanced studies in molecular physics, atmospheric science, and chemical analysis, including mixture identification and quantitative spectroscopy. The demonstrated system represents a promising step toward versatile, high-precision THz spectrometry for a wide range of scientific and technological applications.
Acknowledgments
The authors would also like to acknowledge the financial support of the French Agence Nationale de la Recherche via TIGER (ANR-21-CE30-0048) and HEROES (ANR-16-CE30 0020). Ardhendu Pal would like to acknowledge CPER WAVETECH PROGRAMME for his Postdoctoral Fellowship.
References
[1] F. Hindle, A. Khabbaz, A. Roucou, F.J. Lampin and G. Mouret 2025. Terahertz Frequency Comb High-Resolution Heterodyne Spectrometer. IEEE Transactions on Terahertz Science and Technology.
[2] www.mpifr-bonn.mpg.de/7081687/qffts4g
How to cite: Pal, A., Simon, F., Hindle, F., and Mouret, G.: THz frequency comb high-resolution heterodyne detection coupled with fast Fourier spectrometer, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5300, https://doi.org/10.5194/egusphere-egu26-5300, 2026.
The O2 collision-induced absorption(CIA) band near 1.06 μm plays a crucial role in evaluating planetary habitability. This band consists of the transition superimposed on a broad CIA structure. Although the O2 CIA in this band is much weaker than that near 1.27 μm and the A band (760 nm), accurate binary coefficients, , were measured using a custom designed, high-sensitivity cavity ring-down spectroscopy (CRDS) setup developed in our laboratory under low density (< 1 amagat) and at room temperature (296 K) for pure O2 and O2/N2 mixtures over the range 9120-9820 cm-1. As expected, excellent agreement, generally within 1%, was observed among measurements performed at different densities, benefiting from the use of Ar as a baseline reference and low-density measurements that suppress Rayleigh scattering and line mixing, thereby reducing the uncertainty of the retrieved results. The retrieved were compared with the values from LBLRTM simulations, HITRAN, and ab initio calculations. The reported here are found to be in good agreement with these values. In particular, excellent agreement within 0.2% is observed between our measurements and LBLRTM simulations at the band center. The integrated CIA band intensity, , exceeds the corresponding values in HITRAN, LBLRTM simulations, and the ab initio calculations by about 28.6%, 44.2%, and 16.5%, respectively.
How to cite: Huang, Y., Dong, H., Huang, H., Cao, Z., and Wang, Y.: Accurate Laboratory Measurement of Collision-Induced Absorption of O2 near 1.06 µm, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16336, https://doi.org/10.5194/egusphere-egu26-16336, 2026.
Correspondence: Min Qin(mqin@aiofm.ac.cn) , Pinhua Xie (phxie@aiofm.ac.cn)
Iodine (I) in the atmosphere not only provides an important source of iodine for mammals, but also affects the catalytic depletion of ozone in the atmosphere, the production of important free radicals such as OH, and the formation of marine aerosols. Its atmospheric chemical behavior has been an important topic in atmospheric chemistry research in recent years. Research has found that iodine oxide plays an important role in the formation process of ultrafine aerosol particles (particle size between 3-10 nm), especially in the oceanic boundary layer (i.e. iodine oxide particles, IOPs). The chemical composition analysis of new particles in the ocean boundary layer shows that the nucleation and growth of particles are mainly controlled by condensable iodine vapor. The ship measurement results of halogen oxides in the Arctic high boundary layer show that iodine will exacerbate the depletion of tropospheric ozone in spring. The chemical reaction between iodine and ozone is the second largest factor causing ozone loss, second only to the loss caused by ozone photolysis. Currently, most laboratories primarily rely on chemical methods for iodine analysis. However, the high cost of associated instruments makes it difficult to meet routine analytical demands. In the field of optical methods, various spectroscopic techniques have been developed and applied, such as long-path differential optical absorption spectroscopy (DOAS), cavity ring-down spectroscopy (CRDS), and cavity-enhanced absorption spectroscopy (CEAS).This study used Broadband cavity-enhanced absorption spectroscopy (BBCEAS) technology. A homemade dual-cavity BBCEAS system integrated with green and blue LEDs enables in situ simultaneous measurement of I₂ and IO (iodine monoxide). With a time resolution of 60 seconds, The limit of detection (2σ) of the measurement system reached 1.13 pptv for I₂ and 1.31 pptv for IO. It has already been applied in laboratory-based measurement experiments.
How to cite: Ren, E., Qin, M., Fang, W., Xie, J., Han, B., Shao, D., and Xie, P.: Quantitative determination of I2/IO using a dual-channel BBCEAS system and its laboratory validation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17210, https://doi.org/10.5194/egusphere-egu26-17210, 2026.
Terahertz (THz) spectroscopy can distinguish polar molecules in gas mixtures thanks to the narrow and intense transitions specific to this band. Thus, rotational transitions of many atmospheric species can be accurately measured. CF4, the most abundant perfluorocarbon in the atmosphere, is a highly stable greenhouse gas, with an atmospheric lifetime of 50,000 years and a warming potential much greater than that of CO2. Accurate quantification of CF4 is essential for understanding its contribution to the radiative forcing budget. However, this molecule has a very weak dipolar moment induced by centrifugal distortion, which makes its spectroscopic study challenging in the THz domain.
Here, we present the specific features of an ultrasensitive, high-finesse cavity spectrometer that enables both Cavity Enhanced Absorption Spectroscopy (CEAS) and Cavity Ring-Down Spectroscopy (CRDS) measurements. This setup has enabled highly resolved spectra of the weak transitions of CF4. More than 50 pure rotational ν3 − ν3 lines have been measured, yielding both position and intensity data with unequalled precision. CRDS enabled the absolute intensities, used in the global fit, to be determined. Finally, the updated TFMeCaSDa database is available for future spectroscopic and monitoring activities.
Further challenging work is underway with GeH4, a compound primarily used for manufacturing high-performance integrated circuits in the semiconductor industry. CEAS measurements of some transitions with very low intensities are presented here. Spectroscopic analysis is ongoing.
How to cite: Simon, F., Pal, A., Cuisset, A., Hindle, F., Mouret, G., Rey, M., Boudon, V., and Richard, C.: A terahertz cavity for accurate spectroscopic measurements of atmospheric species, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14458, https://doi.org/10.5194/egusphere-egu26-14458, 2026.
We present a novel low-cost and compact method for detecting trace gases using their absorption features in the sub-THz region. Conventionally, work in this area uses free space quasi-optics which have inconveniently large and potentially costly instrumentation. This is due to the drawbacks of the optical setup which require both long beam paths and large optics in this frequency range. Instead, we have developed a novel system that confines the radiation to a specially designed waveguide meaning long pathlengths (and therefore high SNR) can be achieved in a relatively small instrument and no optics or alignment are required. A flow of gas is introduced into the waveguide which changes the spectral transmission loss. This technology has been demonstrated in the lab and can be applied to any gases with absorption features in the sub-THz region. A deployable instrument has been completed, and we aim to engage in field testing in the near future.
How to cite: McCormack, E., Lane, B., Blackshaw, S., Obeed, A., Hunyor, P., McPheat, R., and Gerber, D.: The development of a rugged, compact gas spectrometer using a sub-THz waveguide, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20291, https://doi.org/10.5194/egusphere-egu26-20291, 2026.
Aerosols are a key component of the atmosphere, influencing Earth’s climate through direct and indirect radiative effects, while also playing a major role in air quality and human health. Despite their importance, aerosols remain the largest source of uncertainty in estimates of climatic radiative forcing. This uncertainty arises from their complex chemical and physical properties, diverse sources, and strong spatio-temporal variability, all of which challenge accurate representation in atmospheric models. A crucial aspect of resolving model uncertainty of aerosols is the accurate representation of their microphysical properties, which control optical behavior and radiative effects. This study aims to address this uncertainty by applying a perturbed parameter ensemble (PPE) approach using the LOTOS-EUROS chemistry transport model. The analysis focuses on elemental carbon (EC) and mineral dust aerosols. Key microphysical parameters such as particle radius, geometric standard deviation (sigma) in the assumed lognormal particle size distribution, real and imaginary parts of the refractive index, and mass concentrations will be perturbed within physically plausible ranges. Uncertainty ranges for the refractive index are sourced from the Models, In situ, and Remote sensing of Aerosols (MIRA) international working group. Emulators trained on the ensemble simulations will provide a fast, statistical representation of modeled absorbing aerosol optical depth (AAOD), enabling efficient sampling of high-dimensional parameter space. Model results will be constrained using surface measurements of black carbon and mineral dust mass concentrations from EBAS, together with AAOD observations from AERONET. These combined constraints help reduce compensating bias between aerosol amount and optical efficiency. Overall, this framework will enable a quantitative assessment of uncertainty in modeled aerosol optical properties, identify the parameters that most strongly influence AAOD, and constrain the most realistic parameter ranges. These constraints will improve the representation of the varied aerosol microphysical properties in LOTOS-EUROS, leading to more accurate assumed aerosol optical properties. This is crucial for a useful uptake of remote sensing aerosol data in model evaluations and assimilation approaches.
How to cite: Elliott, K., Henzing, B., Tokaya, J., and Schutgens, N.: OPALE: Reducing Aerosol Optical Property Uncertainty of Elemental Carbon and Mineral Dust in LOTOS-EUROS Using a Perturbed Parameter Ensemble , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18652, https://doi.org/10.5194/egusphere-egu26-18652, 2026.
Ice clouds are a key component in the atmospheric system because of their influence on atmospheric circulation and precipitation. However, studying ice cloud microphysical processes and radiative impact remains a challenge, in part because ice crystal non-sphericity is not well-represented in models. Remote sensing retrievals can help constrain and characterize the ice crystal complexity within high clouds, through measurements of polarized radiance. Although both previous and current satellite instruments have used polarization measurements to achieve this goal, their spectral ranges have been limited to the shortwave (SW) (e.g., POLDER, CALIPSO, and HARP2) or microwave (e.g., GPM-GMI) ranges. Polarization has not previously been remotely sensed in the longwave infrared (LWIR) spectral range, where ice clouds exhibit strong signatures from both emission and scattering.
Development of the CHanneled Infrared Polarimeter (CHIRP) instrument aims to characterize LWIR polarized radiances from ice clouds. Here, we provide a set of LWIR polarized radiative transfer simulations for various ice cloud configurations under tropical conditions. Using a polarized Markov chain radiative transfer model, we compute the polarization difference (PD), defined as the difference between the vertically and horizontally polarized brightness temperatures, at three LWIR wavelengths (8.5, 9.5, and 10.5 µm) and for a wide range of ice cloud optical depths (τ = 0.05–20), cloud-top heights (8.5–15.5 km), view zenith angles (0–70°), effective radii (reff = 5-90 µm), and randomly oriented ice crystal habits (droxtals, plates, solid columns, bullet rosettes, and 8-column aggregates). Relatively small but distinct negative PD signatures (> -1 K, horizontal polarization) are found in ice clouds across different ice habits at τ ~ 5–7 and for the smallest and largest crystals (reff < 20 µm, reff > 40 µm). Non-negligible PD signatures also emerge at oblique viewing angles (vza = 50º–70º) and from clouds at altitudes near the tropopause. Additionally, we discuss preliminary work to run analogous parameter sweeps in the LWIR for oriented ice crystals.
How to cite: Sepúlveda Araya, E. I., Sullivan, S., Xu, F., Wu, D., Gong, J., and Kupinski, M.: Influence of Ice Crystal Morphology on Simulated Longwave Infrared Polarized Radiance of Ice Clouds, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16048, https://doi.org/10.5194/egusphere-egu26-16048, 2026.
Atmospheric aerosols represent a critical component of the Earth–atmosphere system, modulating radiative climate forcing through both direct and indirect pathways. Consequently, accurate measurement of their physical and optical properties has long been a primary focus of international aerosol research. Nevertheless, substantial uncertainties persist in current observational techniques and numerical models, particularly with respect to aerosol size distribution, morphology, and optical characteristics. These uncertainties propagate through retrieval algorithms and radiative transfer calculations, ultimately compromising the reliability of radiative forcing estimates and climate projections.
In this study, we address the challenge of characterizing non-spherical aerosol particles through advanced in situ measurement techniques. We first present a high-resolution aerosol imaging system that integrates optical microscopy with real-time computer-vision analysis (Dong, et al., IEEE Trans. Instrum. Meas., 2025). Leveraging advanced image processing algorithms, this instrument delivers high spatiotemporal resolution measurements of particle size, morphology, and number concentration, thereby enabling precise quantification of complex, non-spherical geometries and their dynamic evolution.
Complementing the imaging system, we introduce a fully automated laser scattering measurement instrument designed to acquire aerosol scattering phase functions with exceptional angular coverage (5°–357°) and spectral versatility ranging from the ultraviolet to the near-infrared (Dong, et al., Chin. Opt. Lett., 2025). These high-fidelity phase function measurements provide robust constraints on the angular scattering behavior of non-spherical particles.
By integrating these two complementary platforms, we achieve comprehensive characterization of aerosol particles across a diameter range of 0.2-186 μm. The resulting dataset includes five size descriptors, four independent shape descriptors, scattering phase functions, scattering coefficients, asymmetry parameters, and number concentrations spanning 0 to 108 particles/cm3. Collectively, this synergistic observational framework yields concurrent, high-accuracy determinations of aerosol geometric and optical properties.
These laboratory- and field-validated observations obtained from our integrated systems are expected to substantially reduce uncertainties in radiative transfer simulations, improve estimates of aerosol radiative effects, and deepen our understanding of aerosol–radiation–cloud interactions.
Refs:
1. Li Dong, Yong Han, Maohai Hu, et al. Fast Atmospheric Aerosol Size and Shape Imaging Instrument: Design, Calibration, and Intelligent Interaction[J]. IEEE Transactions on Instrumentation and Measurement, 2025, 74: 1-17.
2. Li Dong, Yong Han, and Yurong Zhang. Development of a multi-wavelength near-full-angle aerosol scattering phase function laser measurement system[J]. Chinese Optics Letters, 2025, 23(11): 111203.
How to cite: Dong, L. and Han, Y.: A Synergistic Characterization Method for the Geometric Structure and Optical Response of Non-spherical Aerosols, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1548, https://doi.org/10.5194/egusphere-egu26-1548, 2026.
Mineral dust is a major component of atmospheric aerosol loading and typically shows high depolarization ratios because of its irregular particle shape. The depolarization ratio measurements make mineral dust easier to distinguish from other aerosols in lidar observations. However, the complex and diverse morphology of dust particles is difficult to represent accurately in scattering models used for lidar retrievals, which introduces uncertainties in the derived microphysical properties. To address these limitations a new scattering laboratory has been established under the course of the project OLALA (Optical Lab for Lidar Applications). The goal is to perform controlled measurements that will help to better constrain scattering models and improve aerosol property retrievals from lidar observations. Using this experimental setup, an extensive dataset of backscattering properties of size resolved mineral dust particles will be obtained at three standard lidar wavelengths: 355 nm, 532 nm, and 1064 nm.
At present, the laboratory setup is fully operational at a single wavelength of 532 nm. Our optical setup uses a continuous wave laser at 532 nm as the light source and a 50:50 beam splitter to acquire the exact backscattering geometry (180±0.2°). In the receiver section, a polarizing beam splitter cube separates the parallel and perpendicular component of backscattered light and directs them towards their respective detection channels. Our aerosol chamber is a vertically oriented 1 m long tube with an inner diameter of 1.5 cm. The total particle concentration entering the aerosol chamber is monitored with a condensation particle counter (CPC) and at the exit of the aerosol tube an optical particle sizer (OPS) measures the concentration and size distribution of aerosol particles. A differential mobility analyzer is used to select particles of a defined mobility diameter, producing monodisperse aerosols.
We have performed initial measurements with different types of aerosols to demonstrate the performance and potential of our setup. For spherical particles we used polystyrene latex particles of 1000 nm diameter and ammonium sulfate particles of 250 nm diameter and observed very low depolarization ratios of less than 2%. For non-spherical particles we used sodium chloride, Arizona Test Dust and German soil dust at four different sizes of 250 nm, 450 nm, 650 nm and 800 nm in diameter. We observed an increasing trend in the depolarization ratio with an increase in particle size for non-spherical fine mode aerosol samples.
After the successful implementation of the 532 nm setup, we are now focused on extending the optical setup by incorporating 1064 nm and 355 nm wavelengths. Once the triple wavelength setup is operational, we plan to perform measurements with natural mineral dust samples collected from different deserts around the globe.
How to cite: Semwal, E., Haarig, M., Hartmann, M., Engelmann, R., Althausen, D., Wex, H., and Oppermann, T.: OLALA First Results: Depolarization Ratios of Fine Mode Aerosol Particles, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19391, https://doi.org/10.5194/egusphere-egu26-19391, 2026.
Atmospheric aerosol particles, both organic and inorganic, play a critical role in driving climate change and pose significant risks to human health. Among the major sources of these particles are biomass burning and combustion processes, which release inorganic carbonaceous aerosols (IC) such as black carbon (BC), carbon nanotubes (CNT), and graphite. Despite their environmental and health impacts, the physicochemical properties of IC aerosols remain poorly understood, hindering accurate assessments of their effects on Earth’s radiative balance and public health. In this study, we introduce a novel approach for the in-situ, real-time quantitative analysis of IC aerosols, including their 3D size, shape, phase, and surface properties, along with 4D tracking. This is achieved using an advanced Nano-digital in-line holography microscope (AI-Nano-DIHM) in both air and water environments, under both stationary and dynamic conditions. This study highlights the potential of AI-Nano-DIHM as a cost-effective, rapid, and precise tool for real-time characterization of IC aerosols, offering significant advancements for environmental monitoring and health-related research.
How to cite: Nasreddine, Z., Pal, D., and Ariya, P.: Innovative AI-Driven Approach for Real-Time 4D Tracking and Physicochemical Analysis of Inorganic Carbonaceous Aerosols in Air and Water, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4105, https://doi.org/10.5194/egusphere-egu26-4105, 2026.
Accurate in-situ measurement of cloud microphysical properties, such as the water content, is essential in the research and modelling of cloud and precipitation formation, or the prediction of macrophysical properties, e.g., cloud radiative properties.
In mixed-phase clouds, where ice crystals coexist with supercooled liquid droplets on different scales and with varying mixing ratio, accurate knowledge of this mixing ratio of cloud liquid water content to ice water content is important, in particular for advancing radar, lidar and satellite retrievals.
Based on previously presented results demonstrating the possibility of measuring the mass concentration of liquid water droplet streams in an integrating sphere absorption meter [1][2], we present the progress made and first validation results of a novel optical instrument for bulk in-situ cloud water condensed phase ratio measurement. The proposed instrument features a flow-through type integrating cavity for differential, near-infrared optical absorption measurement. Such cavities, by nature of their light homogenizing property, largely eliminate particle scattering contributions, which typically prohibit simple optical absorption measurement of particles. This promises to allow direct and in-situ determination of the fractions of both condensed phases in mixed-phase clouds via their optical absorption. The current design is limited to drop and particle sizes below 200 µm due to absorption saturation, as determined from Mie calculations for the chosen optical wavelengths. The lower water content detection limit is determined by speckle noise generated by the integrating cavity, which is subject to presented optimization efforts. We also present numerical Monte-Carlo based ray tracing simulations of the integrating cavity geometry for sensitivity and signal-to-noise ratio optimization.
[1] Grafl, M., Bergmann, A., & Lang, B. (2021). Validation of Integrating Cavity Absorption Spectroscopy for Cloud and Aerosol Mass Concentration Measurement: 39th Annual Meeting of the American Association for Aerosol Research. 153.
[2] Lang, B.,, Bergmann, A. (2024). Flow-Through Integrating Cavity Optical Absorption Spectrometer for In-Situ Cloud Water Condensed Phase Composition Measurement: Design Constraints and Initial Validation. 42nd Annual Meeting of the American Association for Aerosol Research.
How to cite: Lang, B., Medebach, M., and Bergmann, A.: Progress on a Flow-Through Integrating Cavity Optical Absorption Spectrometer for In-Situ Cloud Water Condensed Phase Ratio Measurement, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21368, https://doi.org/10.5194/egusphere-egu26-21368, 2026.
Thermospheric winds play a crucial role in transporting momentum and energy in the upper atmosphere, influencing both its composition and dynamics, with direct implications for satellite operations and global communication systems. The Fabry–Perot interferometer (FPI) is a key remote-sensing instrument for measuring thermospheric winds by observing Doppler shifts and Doppler broadening of naturally occurring airglow emissions. In March 2024, DLR installed a 630 nm FPI (SOFPIT) on Tenerife (28.29° N, 16.63° W; 32.79° N, 60.75° E geomagnetic), enabling high-resolution observations of upper-atmosphere winds.
We implemented two retrieval methods tailored to the SOFPIT instrument. The first method, based on Shiokawa et al. (2012), compares images taken in opposite directions (east–west, north–south), assuming wind uniformity across the field of view. The second method, following Makela et al. (2011), uses a forward model simulating the instrument response for given wind and temperature values; observed images are then fitted to the model to infer winds, requiring a zero-wind reference for absolute calibration.
Both approaches have been successfully applied to the entire SOFPIT dataset since the start of observations, demonstrating the robustness and reliability of the retrieval techniques. These results confirm that the instrument can consistently measure thermospheric winds and provide a solid foundation for ongoing improvements in data processing and calibration.
Our study highlights the effectiveness of FPIs for detailed monitoring of upper-atmosphere dynamics. Such measurements are essential for improving our understanding of thermospheric behavior and supporting operational forecasting in space weather and satellite mission planning.
How to cite: Gauthier, A., Geach, C., Borries, C., and Stober, G.: Thermospheric wind retrievals from the SOFPIT Fabry–Perot interferometer at 630 nm, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22480, https://doi.org/10.5194/egusphere-egu26-22480, 2026.
