Top-of-Atmosphere Albedo Estimation from Angular Distribution Models Using Scene Identification from Satellite Cloud Property Retrievals

International audienceThe next generation of earth radiation budget satellite instruments will routinely merge estimates of global top-of-atmosphere radiative fluxes with cloud properties. This information will offer many new opportunities for validating radiative transfer models and cloud parameterizations in climate models. In this study, five months of Polarization and Directionality of the Earth's Reflectances 670-nm radiance measurements are considered in order to examine how satellite cloud property retrievals can be used to define empirical angular distribution models (ADMs) for estimating top-of-atmosphere albedo. ADMs are defined for 19 scene types defined by satellite retrievals of cloud fraction and cloud optical depth. Two approaches are used to define the ADM scene types. The first assumes there are no biases in the retrieved cloud properties and defines ADMs for fixed discrete intervals of cloud fraction and cloud optical depth (fixed-τ approach). The second approach involves the same cloud fraction intervals, but uses percentile intervals of cloud optical depth instead (percentile-τ approach). Albedos generated using these methods are compared with albedos inferred directly from the mean observed reflectance field

Comparison of POLDER apparent and corrected oxygen pressure to ARM/MMCR cloud boundary pressures

International audiencePOLDER (POLarization and Directionality of the Earth's Reflectances) cloud oxygen pressures are compared to cloud boundary pressures obtained from the combination of Lidar and Millimeter Wave Cloud Radar ground measurements located at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site. Without ground reflection correction, the apparent pressures are found to be closer to the mean cloud pressure than to the cloud top pressure. Nevertheless, for almost a quarter of our comparison cases the apparent pressure level is found to be below the cloud base level. This problem practically disappears applying a simple correction for the surface reflection effect. The corrected oxygen pressures are then found to be very close (12 hPa on average) to the mean cloud pressure

Inferences about pressures and vertical extension of cloud layers from POLDER3/PARASOL measurements in the oxygen A-band

We present new inferences about cloud vertical structures from multidirectionnal measurements in the oxygen A-band. The analysis of collocated data provided by instruments onboard satellite platforms within the A-Train, as well as simulations have shown that for monolayered clouds, the cloud oxygen pressure PO2PO2 derived from the POLDER3 instrument was sensitive to the cloud vertical structure in two ways: First, PO2PO2 is actually close to the pressure of the geometrical middle of cloud and we propose a method to correct it to get the cloud top pressure (CTP), and then to obtain the cloud geometrical extent. Second, for the liquid water clouds, the angular standard deviation σPO2σPO2 of PO2PO2 is correlated with the geometrical extent of cloud layers, which makes possible a second estimation of the cloud geometrical thickness. The determination of the vertical location of cloud layers from passive measurements, eventually completed from other observations, would be useful in many applications for which cloud macrophysical properties are neede

Cloud cover observed simultaneously from POLDER and METEOSAT

International audienceThe POLDER instrument that was aboard the Japanese ADEOS platform between August 1996 and June 1997. is designed to the global observations of the polarisation and directionality of the sun-light reflected by the Earth-atmosphere system. The cloud detection from POLDER takes advantage of the original capabilities of the instrument (spectral polarisation and directionality). This cloud detection scheme uses 5 threshold tests based on pressure, reflectance, polarised reflectance and spectral variability. The results of the POLDER cloud detection scheme are compared to those of the LMD dynamical clustering method applied to visible and infrared METEOSAT data and local spatial variability of these two parameters. Special focus is given to the detection capabilities of the two kind of measurements for cloud situations such as small cumulus, thin cirrus and multilayered cloud cover. Results of this comparison would give some insight on the behaviour of the International Satellite Cloud Climatology Project (ISCCP) cloud detection scheme built mainly from visible and infrared measurements

Peut-on diminuer les comportements sexuels des porcs mâles non-castrés par l’ajout de poudre de fruits du gattilier (Vitex agnus castus) dans l’aliment ?

texte issu des actes à venir + doi dans animal sciences proceedings pour le résumé anglaisInternational audienceContexte de l'étude Les comportements sexuels des porcs mâles non castrés peuvent blesser les congénères et diminuer leur bien-être. La mise à disposition de grandes surfaces, comme en élevage biologique, semble permettre une expression accrue de ces comportements. Le gattilier (Vitex agnus castus), une plante connue sous le nom de Poivre des moines, aurait des propriétés anaphrodisiaques. Il n'existe pas de preuve scientifique, mais il a été montré que cette plante permet de moduler la fonction de reproduction des mammifères femelles. Le gattilier pourrait donc permettre de réduire les comportements sexuels des porcs mâles non castrés d'une façon naturelle qui pourrait convenir à tout type d'élevage dont l'élevage biologique. Objectifs Déterminer si l'ajout de poudre de fruits du gattilier (Vitex agnus castus) sur l'aliment permet de diminuer les comportements de monte des porcs mâles non castrés élevés en système biologiqu

Apparent pressure derived from ADEOS-POLDER observations in the oxygen A-band over ocean

International audienceThe POLDER radiometer was on board the ADEOS satellite from August 1996 to June 1997. This instrument measures radiances in eight narrow spectral bands of the visible and near infrared spectrum. Two of them are centered on the O2 A-band in order to infer cloud pressure. By assuming the atmosphere behaves as a pure absorbing medium overlying a perfect reflector, an "apparent" pressure Papp is derived from POLDER data. For validation purposes, Papp is first compared to the sea-surface pressure Ps for clear-sky conditions; Papp is found to be close to Ps (within ∼30 hPa) for measurements in the sunglint region. For overcast conditions, Papp differs from the cloud-top pressure mainly because of multiple scattering inside the cloud. When Papp is compared to the cloud pressure determined from brightness temperature measurements, large differences are observed (typically 180 hPa)

First results of the "Earth Radiation Budget and Clouds" operational algorithm

International audienceThe POLDER instrument is devoted to global observations of the solar radiation reflected by the Earth-atmosphere system. Algorithms of the "Earth Radiation Budget and Clouds" processing line implemented at the French Space Center are applied to ADEOS-POLDER data. First results on derived cloud properties are presented from POLDER level 2 data of 10 November 1996 and level 3 products of June 1997. A good correlation is observed between the POLDER cloud detection algorithm and the Dynamical Clustering Method applied to METEOSAT data. The multidirectional capability of POLDER appears useful to check schemes of cloud optical thickness retrieval. As expected, a water droplet model is suitable for liquid water clouds and inadequate for ice clouds. That indirectly validates the algorithm of cloud phase recognition. An apparent pressure is derived from O2-absorption measurements and a Rayleigh cloud pressure from polarization observations. For overcast conditions, the apparent pressure is larger (by more than 100 hPa) than the Rayleigh pressure chiefly due to the photon penetration effect. For partly cloudy conditions, it can be larger or weaker depending on the surface reflectivity. Preliminary comparisons between POLDER and ISCCP monthly mean products outline some differences resulting in part from the original characteristics of POLDE

Cloud heterogeneity on cloud and aerosol above cloud properties retrieved from simulated total and polarized reflectances

International audienceSimulations of total and polarized cloud re-flectance angular signatures such as the ones measured by the multi-angular and polarized radiometer POLDER3/PARASOL are used to evaluate cloud hetero-geneity effects on cloud parameter retrievals. Effects on optical thickness, albedo, effective radius and variance of the cloud droplet size distribution and aerosol parameters above cloud are analyzed. Three different clouds that have the same mean optical thicknesses were generated: the first with a flat top, the second with a bumpy top and the last with a fractional cloud cover. At small scale (50 m), for oblique solar incidence , the illumination effects lead to higher total but also polarized reflectances. The polarized reflectances even reach values that cannot be predicted by the 1-D homogeneous cloud assumption. At the POLDER scale (7 km × 7 km), the angular signature is modified by a combination of the plane-parallel bias and the shadowing and illumination effects. In order to quantify effects of cloud heterogeneity on operational products, we ran the POLDER operational algorithms on the simulated reflectances to retrieve the cloud optical thickness and albedo. Results show that the cloud optical thickness is greatly affected: biases can reach up to −70, −50 or +40 % for backward, nadir and forward viewing directions , respectively. Concerning the albedo of the cloudy scenes, the errors are smaller, between −4.7 % for solar incidence angle of 20° and up to about +8 % for solar incidence angle of 60°. We also tested the heterogeneity effects on new algorithms that allow retrieving cloud droplet size distribution and cloud top pressures and also aerosol above clouds. Contrary to the bi-spectral method, the retrieved cloud droplet size parameters are not significantly affected by the cloud heterogeneity, which proves to be a great advantage of using polarized measurements. However, the cloud top pressure obtained from molecular scattering in the forward direction can be biased up to about 60 hPa (around 550 m). Concerning the aerosol optical thickness (AOT) above cloud, the results are different depending on the available angular information. Above the fractional cloud, when only side scattering angles between 100 and 130° are available, the AOT is underestimated because of the plane-parallel bias. However, for solar zenith angle of 60° it is overestimated because the polarized reflectances are increased in forward directions