Laboratory Evaluation of the (355, 532) nm Particle Depolarization Ratio of Pure Pollen at 180.0° Lidar Backscattering Angle

While pollen is expected to impact public human health and the Earth’s climate more and more in the coming decades, lidar remote sensing of pollen has become an important developing research field. To differentiate among the pollen taxa, a polarization lidar is an interesting tool since pollen exhibit non-spherical complex shapes. A key attribute is thus the lidar particle depolarization ratio (PDR) of pollen, which is however difficult to quantify as pollen are large and complex-shaped particles, far beyond the reach of light scattering numerical simulations. In this paper, a laboratory π-polarimeter is used to accurately evaluate the PDR of pure pollen, for the first time at the lidar exact backscattering angle of 180.0°. We hence reveal the lidar PDR of pure ragweed, ash, birch, pine, cypress and spruce pollens at 355 and 532 nm lidar wavelengths, as presented at the ELC 2021 conference. A striking result is the spectral dependence of the lidar PDR, highlighting the importance of dual-wavelength (or more) polarization lidars to identify pollen taxa. These spectral and polarimetric fingerprints of pure pollen, as they are accurate, can be used by the lidar community to invert multi-wavelength lidar polarization measurements involving pollen

Cavités de haute finesse pour la spectroscopie d'absorption haute sensibilité et haute précision (application à l'étude de molécules d'intérêt atmosphérique)

La haute sensibilité permise par l'emploi des cavités optiques est exploitée pour caractériser la signature de molécules d'intérêt atmosphérique. Deux méthodologies sont abordées. Tout d'abord, la technique CW-CRDS est utilisée pour étudier l'évolution avec la pression et la température des spectres atmosphériques de la vapeur d'eau dans le proche infrarouge. Cette étude, destinée à calibrer des mesures par Lidar, entre dans le cadre de la mission WALES proposée par l'Agence Spatiale Européenne. Ensuite, la technique OF-CEAS et ses performances pour la spectroscopie sont mises en évidence avec la bande B de l'oxygène dans le rouge. Cette technique repose sur un schéma d'injection avec rétroaction optique qui permet d'augmenter la cohérence de l'émission laser et mesurer les maxima de transmission des modes. La linéarité du peigne de mode de la cavité est exploitée grâce à une acquisition mode par mode qui permet la mesure de "pressure shifts" de l'oxygène avec une précision recordLYON1-BU.Sciences (692662101) / SudocSudocFranceF

Laboratory Evaluation of the (355, 532) nm Particle Depolarization Ratio of Pure Pollen at 180.0° Lidar Backscattering Angle

While pollen is expected to impact public human health and the Earth’s climate more and more in the coming decades, lidar remote sensing of pollen has become an important developing research field. To differentiate among the pollen taxa, a polarization lidar is an interesting tool since pollen exhibit non-spherical complex shapes. A key attribute is thus the lidar particle depolarization ratio (PDR) of pollen, which is however difficult to quantify as pollen are large and complex-shaped particles, far beyond the reach of light scattering numerical simulations. In this paper, a laboratory π-polarimeter is used to accurately evaluate the PDR of pure pollen, for the first time at the lidar exact backscattering angle of 180.0°. We hence reveal the lidar PDR of pure ragweed, ash, birch, pine, cypress and spruce pollens at 355 and 532 nm lidar wavelengths, as presented at the ELC 2021 conference. A striking result is the spectral dependence of the lidar PDR, highlighting the importance of dual-wavelength (or more) polarization lidars to identify pollen taxa. These spectral and polarimetric fingerprints of pure pollen, as they are accurate, can be used by the lidar community to invert multi-wavelength lidar polarization measurements involving pollen

Towards DCS in the UV Spectral Range for Remote Sensing of Atmospheric Trace Gases

The development of increasingly sensitive and robust instruments and new methodologies are essential to improve our understanding of the Earth’s climate and air pollution. In this context, Dual-Comb spectroscopy (DCS) has been successfully demonstrated as a remote laser-based instrument to probe infrared absorbing species such as greenhouse gases. We present here a study of the sensitivity of Dual-Comb spectroscopy to remotely monitor atmospheric gases focusing on molecules that absorb in the ultraviolet domain, where the most reactive molecules of the atmosphere (OH, HONO, BrO...) have their highest absorption cross-sections. We assess the achievable signal-to-noise ratio (SNR) and the corresponding minimum absorption sensitivity of DCS in the ultraviolet range. We propose a potential light source for remote sensing UV-DCS and discuss the degree of immunity of UV-DCS to atmospheric turbulences. We show that the characteristics of the currently available UV sources are compatible with the unambiguous identification of UV absorbing gases by UV-DCS

Atmospheric aerosol size retrieval from LIDAR data applying genetic algorithm approach

International audienceIn this paper we present a novel approach using a genetic algorithm (GA) to solve the LIDAR "ill-problem". It is inverting aerosol size distribution from multi-wavelengths Lidar data in the UV-VIS-IR spectral range. This method do not need any predefined size distribution shape and is also running with data having poor S/N. Numerical convergence test of the GA have been done on both simulated data and on Lidar field measurements performed during the French POVA Campaign. It shows that size distribution is retrieved in millisecond rage, which represent a considerably decreasing in computing time consuming. Comparison between GA size distribution retrieval and SMPS ground-based measurements has been done showing an excellent agreement

Atmospheric non-spherical particles optical properties from UV-polarization lidar and scattering matrix

International audienceIn this contribution, the optical backscattering properties of atmospheric non-spherical particles are analyzed after long-range transport with a highly sensitive and accurate UV-polarization lidar. Far from the source region, the aerosol cloud is considered as a mixture of spherical (s) and non-spherical (ns) particles. Aerosols UV-depolarization serves as an independent means to discriminate ns from s-atmospheric particles. Vertical profiles of aerosols backscattering coefficient βa and UV-depolarization ratio δa are provided for two ns-particles case studies, on volcanic ash and desert dust, in the troposphere of Lyon (45.76°N, 4.83°E, France). Achieved polarization-sensitivity and accuracy allows tracing different atmospheric layers with a 75 m-altitude resolution. The depolarization ratio δa of the mixed (a) = s, ns aerosol cloud is then analyzed in the frame of the scattering matrix formalism. Observed δa-values, which range from a few to 38.5% (19.5%) for volcanic ash (desert dust) particles, only equal the intrinsic depolarization ratio of ns-particles when there is no detectable s-particle, and in the presence of s-particles, δa is always below δa,ns. By coupling our accurate lidar measurements with scattering matrix, we retrieved vertical profiles of backscattering coefficient, specific to ash (dust) particles, which is new. This ash (dust) specificity is then discussed within our error bars. We hence developed a methodology giving access to the number concentration vertical profile of specific particulate matter in the troposphere

18th International Laser Radar Conference

Lidar or laser radar, the depth-resolved remote measurement of atmospheric parameters with optical means, has become an important tool in the field of atmospheric and environmental remote sensing. In this volume the latest progress in the development of lidar methods, experiments, and applications is described. The content is based on selected and thoroughly refereed papers presented at the 18th International Laser Radar Conference, Berlin, 22-26 July 1996. The book is divided into six parts which cover the topics of tropospheric aerosols and clouds, lidar in space, wind, water vapor, troposheric trace gases and plumes, and stratospheric and mesospheric profiling. As a supplement to fundamental lidar textbooks this volume may serve as a guide for scientists, engineers, and graduate students through the blossoming field of modern lidar techniques and their contribution to atmospheric and environmental research

Laboratory evaluation of the scattering matrix elements of mineral dust particles from 176.0 degrees up to 180.0 degrees-exact backscattering angle

International audienceIn this paper, the scattering matrix elements of an ensemble of mineral dust particles are for the first time evaluated in laboratory for scattering angles ranging from 176.0° to the π-backscattering angle of 180.0° with a high angular resolution of 0.4° and compared with the outputs of T-matrix numerical code. Elastic light scattering is addressed at near and exact backscattering angles with a newly-built laboratory polarimeter, validated on spherical particles following the Lorenz–Mie theory. The ratios fij(θ) = Fij(θ)/F11(θ) of the scattering matrix elements of mineral dust particles are then precisely evaluated in laboratory from 176.0° up to 180.0° with a 0.4° angular resolution (even 0.2° between 179.2° and 180.0°), which is new. When approaching the π-backscattering angle, the slopes of the scattering matrix elements are almost zero, as theoretically predicted by Hovenier and Guirado [17]. Moreover, our laboratory findings are found in good agreement with the outputs of the T-matrix numerical code, showing the ability of the spheroidal model to describe light-scattering by mineral dust also from near to exact backscattering. Atmospheric implications for polarization lidar retrievals are then discussed in terms of linear and circular depolarization ratios for mineral dust. These results, which complement other existing light scattering experiments, may be used to extrapolate light scattering by mineral dust particles up the π-backscattering angle, which is useful in radiative transfer and climatology, in which backscattering is involved