Lidar Ratios for Dust Aerosols Derived From Retrievals of CALIPSO Visible Extinction Profiles Constrained by Optical Depths from MODIS-Aqua and CALIPSO/CloudSat Ocean Surface Reflectance Measurements

CALIPSO's (Cloud Aerosol Lidar Infrared Pathfinder Satellite Observations) analysis algorithms generally require the use of tabulated values of the lidar ratio in order to retrieve aerosol extinction and optical depth from measured profiles of attenuated backscatter. However, for any given time or location, the lidar ratio for a given aerosol type can differ from the tabulated value. To gain some insight as to the extent of the variability, we here calculate the lidar ratio for dust aerosols using aerosol optical depth constraints from two sources. Daytime measurements are constrained using Level 2, Collection 5, 550-nm aerosol optical depth measurements made over the ocean by the MODIS (Moderate Resolution Imaging Spectroradiometer) on board the Aqua satellite, which flies in formation with CALIPSO. We also retrieve lidar ratios from night-time profiles constrained by aerosol column optical depths obtained by analysis of CALIPSO and CloudSat backscatter signals from the ocean surface

Tracking the emission and transport of pollution from wildfires using the IASI CO retrievals: analysis of the summer 2007 Greek fires

International audienceIn this paper, we analyze the performance of the Infrared Atmospheric Sounding Interferometer (IASI), launched in October 2006 on board METOP-A, for the monitoring of carbon monoxide (CO) during extreme fire events, focusing on the record-breaking fires which devastated thousands of square kilometers of forest in Greece during the last week (23–30) of August 2007. After an assessment of the quality of the profiles retrieved using the Fast Optimal Retrievals on Layers for IASI (FORLI) algorithm, the information provided on fire emissions and subsequent pollution outflow is discussed. Large CO plumes were observed above the Mediterranean Basin and North Africa, with total CO columns exceeding 24×1018 molecules/cm2 and absolute volume mixing ratios up to 4 ppmv on the 25 August. Up to 30×1018 molecules/cm2 and 22 ppmv in the lower troposphere are retrieved close to the fires above the Peloponnese, but with larger uncertainty. The average root-mean-square (RMS) difference between simulated and observed spectra is close to the estimated radiometric noise level, slightly increasing (by ~14%) in the fresh fire plumes. CO profiles are retrieved with a vertical resolution of about 8 km, with ~1.7 pieces of independent information on the vertical in the region considered and a maximum sensitivity in the free troposphere (~4–5 km). Using the integrated total amount, the increase in CO burden due to these fires is estimated to 0.321 Tg, ~40% of the total annual anthropogenic emissions in Greece. The patterns of these CO enhancements are in good agreement with the aerosol optical depth (AOD) retrieved from the MODIS measurements, highlighting a rapid transport of trace gases and aerosols across the Mediterranean Basin (less than one day). While the coarse vertical resolution will not allow the location of the exact plume height, the large CO enhancements observed in the lower troposphere are consistent with the maximum aerosol backscatter coefficient at ~2 km detected by the CALIPSO lidar in space (CALIOP)

Chaos, Consternation and CALIPSO Calibration: New Strategies for Calibrating the CALIOP 1064 nm Channel

The very low signal-to-noise ratios of the 1064 nm CALIOP molecular backscatter signal make it effectively impossible to employ the "clear air" normalization technique typically used to calibrate elastic back-scatter lidars. The CALIPSO mission has thus chosen to cross-calibrate their 1064 nm measurements with respect to the 532 nm data using the two-wavelength backscatter from cirrus clouds. In this paper we discuss several known issues in the version 3 CALIOP 1064 nm calibration procedure, and describe the strategies that will be employed in the version 4 data release to surmount these problems

A New Approach for Checking and Complementing CALIPSO Lidar Calibration

We have been studying the backscatter ratio of the two CALIPSO wavelengths for 3 different targets. We are showing the ratio of integrate attenuated backscatter coefficient for cirrus clouds, ocean surface and liquid. Water clouds for one month of nightime data (left:July,right:December), Only opaque cirrus classified as randomly oriented ice[1] are used. For ocean and water clouds, only the clearest shots, determined by a threshold on integrated attenuated backscatter are used. Two things can be immediately observed: 1. A similar trend (black dotted line) is visible using all targets, the color ratio shows a tendency to be higher north and lower south for those two months. 2. The water clouds average value is around 15% lower than ocean surface and cirrus clouds. This is due to the different multiple scattering at 532 nm and 1064 nm [2] which strongly impact the water cloud retrieval. Conclusion: Different targets can be used to improve CALIPSO 1064 nm calibration accuracy. All of them show the signature of an instrumental calibration shift. Multiple scattering introduce a bias in liquid water cloud signal but it still compares very well with all other methods and should not be overlooked. The effect of multiple scattering in liquid and ice clouds will be the subject of future research. If there really is a sampling issue. Combining all methods to increase the sampling, mapping the calibration coefficient or trying to reach an orbit per orbit calibration seems an appropriate way

An Innovative Concept for Spacebased Lidar Measurement of Ocean Carbon Biomass

Beam attenuation coefficient, c, provides an important optical index of plankton standing stocks, such as phytoplankton biomass and total particulate carbon concentration. Unfortunately, c has proven difficult to quantify through remote sensing. Here, we introduce an innovative approach for estimating c using lidar depolarization measurements and diffuse attenuation coefficients from ocean color products or lidar measurements of Brillouin scattering. The new approach is based on a theoretical formula established from Monte Carlo simulations that links the depolarization ratio of sea water to the ratio of diffuse attenuation Kd and beam attenuation C (i.e., a multiple scattering factor). On July 17, 2014, the CALIPSO satellite was tilted 30deg off-nadir for one nighttime orbit in order to minimize ocean surface backscatter and demonstrate the lidar ocean subsurface measurement concept from space. Depolarization ratios of ocean subsurface backscatter are measured accurately. Beam attenuation coefficients computed from the depolarization ratio measurements compare well with empirical estimates from ocean color measurements. We further verify the beam attenuation coefficient retrievals using aircraft-based high spectral resolution lidar (HSRL) data that are collocated with in-water optical measurements

Etude du couplage radar-lidar sur plates-formes spatiales et aeroportees. Application a l'etude des nuages, des aerosols et de leurs interactions

The aerosol and cloud effect on climate is the main uncertainty on global warming prediction through their influence on the solar radiative forcing and their interactions. Using simultaneous lidar, radar and radiometry measurements is one of the path explored by the scientic community to reduce this uncertainty. It is the reason for the development of new instruments onboard the A-Train platforms and the associated development of operational algorithms. Those algorithms possess some intrisic limitation which lead us to revisit the data analysis procedure of the A-Train spaceborne platform (CALIPSO, CLOUDSAT) and to develop our own algorithms through the analysis of sea surface echo, and to identify theoretical multi-wavelength oceanic surface model with self-consistent scattering properties observed by different instruments. Using this model and the observations of the micro-wave radiometer AMSR-E, allowed to improve the calibration procedure of both lidar and radar instruments with the identication of a systematic and high signal to noise ratio calibration reference. This calibration increases the accuracy of physical parameters retrieved on the research operational products and give access to a higher number of derived products. Using the sea surface reference provided by the active (radar) and passive (radiometer) microwave sensors also allows to measure the aerosol optical thickness at the lidar wavelength. This measurement does not use any assumptions on the scatterers microphysical properties, is usable day and night, offers the highest available signal to noise ratio and allows a good aerosol-cloud discrimination with the lidar multispectral vertical information. The comparison with MODIS shows a good statistical agreement. The new methodologies developped for the A-Train offer a complete tool to analyse both vertical structure of aerosols and clouds as well as the aerosol optical thickness over the ocean and liquid water clouds. This opens a new way for aerosol direct radiative forcing quantication, which is out of range of present radiometric measurements. The preliminary studies we conducted confirm the signicant positive radiative forcing on the Gulf of Guinea area in presence of the biomass burning aerosol plumes observed during the AMMA campaign. The negative forcing over the ocean is an order of magnitude lower than the positive forcing over the cloud layers. The positive radiative forcing we observed on the Gulf of Guinea area (between +5 and +10 W/m2 ) is strongly dependent of cloud cover which can be better characterized by the small scale A-Train measurements, and the warming induced by aerosol direct effect must be better parameterized in the climate models. The emission of absorbing aerosols (fire, pollution...) and their long range transport at elevated altitudes when they can stay over clouds, represent a critical burden on the climate system. The present estimation of a global negative forcing of -0. 5 W/m2 to characterize the aerosol radiative effect needs to be carefully examined to the light of this impact.L'effet des aerosols et des nuages sur le climat, qu'il s'agisse de leur forcage radiatif propre ou de leur interactions constitue actuellement la plus grande incertitude du systeme climatique. L'utilisation couplee de nouveaux moyens d'observations comme le lidar ou le radar avec la radiometrie fait partie des pistes de recherches retenues par la communaute scientique pour reduire ces incertitudes justifiant le developpement et la mise en oeuvre de ces nouveaux instruments sur les plates-formes de l'A-Train et le developpement des algorithmes operationnels associes. Ces algorithmes possedent certaines limitations intrinseques, ce qui nous a amene a la revision des methodes d'analyse standard des donnees issues des plates-formes spatiales de l'A-Train (CALIPSO, CLOUDSAT), au developpement de nos propres algorithmes a travers l'etude de l'echo de surface oceanique, et a l'identication d'un modele theorique de diffusion par la surface compatible avec les observations multispectrales de ces instruments actifs. L'utilisation de ce modele avec les observations actives et celles du radiometre micro-onde AMSR-E a permis d'ameliorer les procedures d'etalonnage absolu du lidar et du radar en offrant une reference systematique possedant un important rapport signal sur bruit. L'amelioration de l'etalonnage de ces instruments permet ensuite d'affiner la precision de la restitution des parametres microphysiques dans les produits operationnels de recherche, et doit donner acces a un plus grand nombre de produits derives. La reference de surface issue des mesures des instruments micro-ondes actifs (radar) et passifs (radiometre) permet ainsi de determiner l'epaisseur optique des aerosols aux longueurs d'onde du lidar. Cette methode de restitution ne fait aucune hypothese sur la microphysique des particules diffusantes, est utilisable de jour et de nuit, possede un rapport signal sur bruit important a grande resolution spatiale et offre la possibilite de discriminer les aerosols et les nuages grace aux mesures multispectrales sur la verticale. Les comparaisons avec les mesures du radiometre MODIS montrent un bon accord statistique. Ces mesures d'epaisseur optique au-dessus de l'ocean et des nuages d'eau liquide ouvrent une nouvelle voie pour quantier le forcage radiatif direct des aerosols en presence de nuage, hors de portee des mesures radiometriques actuelles. Les premieres etudes que nous avons effectuees ont confirme que lors des episodes de feux observes pendant la campagne AMMA, le forcage est fortement positif sur le Golfe de Guinee (entre +5 et +10 W/m2 en moyenne diurne). Le forcage negatif en air non-nuageux au-dessus de l'ocean est inferieur d'un ordre de grandeur au forcage positif du aux aerosols transportes au-dessus des nuages. Le forcage radiatif positif observe sur le Golfe de Guinee est ainsi fortement dependant de la couverture nuageuse et les mesures a petite echelle de l'A-Train permettent de mieux le caracteriser a plus grande echelle. Ainsi, le rechauffement induit par l'effet direct des aerosols sera mieux pris en compte dans les modeles climatiques. L'emission d'aerosols absorbants (feux, pollution...) et leur transport a moyenne et grande echelle en altitude representent un point critique de l'evolution du systeme climatique et des interactions environnement-climat. L'hypothese usuellement admise d'un forcage direct negatif de -0, 5 W/m2 pour caracteriser l'effet radiatif des aerosols demande a etre examinee avec attention en etablissant une meilleure quantication de la contribution des aerosols absorbants (d'origine naturelle ou anthropique) au-dessus des nuages a l'echelle globale

Etude du couplage radar-lidar sur plates-formes spatiales et aéroportées (application à l'étude des nuages, des aérosols et de leurs interactions)

L'effet des aérosols et des nuages sur le climat, qu'il s'agisse de leur forçage radiatif propre ou de leur interactions constitue actuellement la plus grande incertitude du système climatique. L'utilisation couplée d'un lidar et d'un radar fait partie des pistes de recherches retenues par la communauté scientifique pour résoudre ces incertitudes, et c'est un des buts justifiant le développement des nouveaux instruments embarqués sur les plates-formes de l'A-Train et le développement des algorithmes opérationnels associés.Ces algorithmes possèdent certaines limitations intrinsèques, ce qui nous a amené à la révision des méthodes d'analyse standard des plates-formes spatiales de l'A-Train (CALIPSO, CLOUDSAT) et au développement de nos propres algorithmes à travers l'étude de l'écho de surface océanique, et à l'identification un modèle théorique de répartition des ondes de gravité et de capillarité compatible avec les observations multispectrales de ces instruments actifs. L'utilisation de ce modèle avec les observations actives et celles du radiomètre micro-onde AMSR-E a permis d'améliorer les procédures d'étalonnage absolu du lidar et du radar en offrant une référence systématique possédant un important rapport signal sur bruit. L'amélioration de l'étalonnage de ces instruments permet ensuite d'améliorer la précision de la restitution des paramètres microphysiques dans les produits opérationnels de recherche, et doit donner accès à un plus grand nombre de produits dérivés.La référence de surface issue des mesures des instruments micro-ondes actifs (radar) et passifs (radiomètre) permet ainsi de déterminer l'épaisseur optique des aérosols aux longueurs d'onde du lidar. Cette méthode de restitution ne fait aucune hypothèse sur la microphysique des particules diffusantes, est utilisable de jour et de nuit, possède un rapport signal sur bruit important à grande résolution spatiale et offre la possibilité de discriminer les aérosols et les nuages grâce aux mesures multispectrales sur la verticale. Les comparaisons avec les mesures du radiomètre MODIS montrent un bon accord statistique.Ces mesures d'épaisseur optique au-dessus de l'océan et des nuages d'eau liquide ouvrent une nouvelle voie pour quantifier le forçage radiatif direct des aérosols en présence de nuage, hors de portée des mesures radiométriques actuelles. Les premières études que nous avons menées ont confirmé que lors des épisodes de feux observés pendant la campagne AMMA, le forçage est fortement positif sur le Golfe de Guinée. Le forçage négatif en air non-nuageux au-dessus de l'océan est inférieur d'un ordre de grandeur à celui positif au-dessus des nuages.Le forçage radiatif positif observé sur le Golfe de Guinée est fortement dépendant de la couverture nuageuse que les mesures à petite échelle de l'A-Train permettent de mieux caractériser, et le réchauffement induit par l'effet direct des aérosols doit être mieux pris en compte dans les modèles climatiques.L'émission d'aérosols absorbants (feux, pollution...) et leur transport à grande échelle représente une contrainte croissante du système climatique et des interactions environnement-climat. L'hypothèse usuellement admise d'un forçage direct négatif de-0,5 W.m-2 pour caractériser l'effet radiatif des aérosols demande à être examinée avec attention.PARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Multi-Instrument Calibration Method Based on a Multiwavelength Ocean Surface Model

International audienceA-Train platforms offer the possibility of measuring the same physical parameters using active and passive instruments, to improve our understanding of geophysical processes in the Earth system. In this letter, a new calibration approach is developed using active [Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) lidar and CloudSat radar] and passive [Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E)] instruments. The parameters of an existing oceanic surface model are first adjusted to give consistent sea surface scattering properties for CALIPSO and CloudSat observations. Revisiting the lidar/radar data analysis procedure using this model, as well as sea surface wind speed, the temperature and water vapor products of the microwave radiometer (AMSR-E) allowed one to refine the calibration factors for both lidar and radar observations in a coherent approach. This study also improves other applications such as the retrieval of atmospheric attenuation from aerosols at optical wavelengths

Innovative retrieval methods of aerosol and cirrus cloud optical depth above water clouds and ocean surface, and its application for ATLID calibration/validation activities.

International audienceWe have developed in the frame of the CALIPSO mission two innovative techniques allowing to derive aerosol and cirrus cloud optical depths from backscatter lidar measurements over ocean surface and water clouds. We will present the underlying principles of the methodologies and how they can be applied to calibration/validation activities for the EarthCare mission, specifically the future ATmospheric LIDar (ATLID) aerosol and cirrus cloud optical depth dataset. We will present several examples of their validation against the measurements from the NASA Langley airborne High Spectral Resolution Lidar (HSRL) and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) space borne Lidar in clear air. We will show how we can validate the ATLID aerosol and cirrus cloud data using column integrated atmospheric optical depths derived from ATLID ocean surface backscatter measurements together with collocated cloud radar ocean surface backscatter cross section or wind speed measurements. We will also show how we can validate the ATLID aerosol and cirrus cloud data using above cloud optical depths derived from layer integrated water cloud ATLID lidar backscatter measurements. Finally, we will also show how we can validate ATLID level 1 data using the lidar backscatter measurements of ocean surface and water clouds when there are no aerosol and cirrus clouds. These different activities will provide a quantification of the accuracy of L1 and L2 space lidar data that ESA will be able to use in future quality assessments

Combination of lidar and radar observations to retrieve microphysical properties of boundary layer clouds using a new analytical approach.

International audienceA case study analysis has been conducted on the diurnal cycle of boundary layer clouds observed at the IPSL station in Palaiseau (France) on the period from the 22 nd to the 26 th March 2004, during the CLOUDNET project. The cloud properties have been analysed using remote sensing (ground based radar and lidar), applying the Klett inversion method in a new way to retrieve microphysical properties of a stratocumulus cloud layer. Comparisons of results obtained on March 24 th at the end of the morning with satellite observations (MODIS) and with forecasts from three numerical models (METEOFRANCE ARPEGE, UKMO Unified Model and ECMWF) are presented and discussed here