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Ice clouds and dust aerosols are two important atmospheric constituents. To reliably assess the radiativeforcings and to accurately infer the microphysical and optical properties of these two atmospheric components, it is necessary to use appropriate optical properties of ice crystals and dust particles. In this talk we will discuss the use of remote sensing techniques based on observations by passive and active sensors to constrain the optical properties. Specifically, we will use the MODIS (Moderate Resolution Imaging Spectroradiometer), POLDER (POLarization and Directionality of the Earth's Reflectances), MISR (Multi-angle Imaging SpectroRadiometer), and CALIOP/CALIPSO (Cloud-Aerosol Lidar with Orthogonal Polarization on the Cloud-Aerosol Lidar with Orthogonal Polarization) measurements in combination of theoretical light scattering simulations to identify the optimal single-scattering properties (extinction coefficient, single-scattering albedo, and phase matrix) of nonspherical/inhomogeneous ice crystals and dust particles.

Assessment of the effect of multiangular polarized incident light on the bidirectional reflectance factor (BRF) of vegetation and soil samples is presented in this paper. The samples were evaluated with a reference to 99% white Spectralon calibration standard in the UV-VIS-NIR spectral range. The BRF of the samples was found to be strongly influenced by the polarization of the incident light at different multiangular geometries.

A laboratory-based Bidirectional Reflectance Factor (BRF) polarization study of vegetation is presented in this paper. The BRF was measured using a short-arc Xenon lamp/monochromator assembly producing a tunable light source with a well-defined spectral bandpass at the following visible and near-infrared wavelengths: 340nm, 470 nm, and 870 nm. All vegetation samples were measured using P and S linearly polarized incident light over a range of incident and scatter angles. By comparing these results, we quantitatively examined how the BRF of the samples depends on the polarization of the incident light. The differences are significant, depend strongly on the incident and scatter angles, and can be as high as 135% at 67 deg incident and 470nm.

Laboratory BRDF measurements of salt pan regolith samples are presented in this study in an effort to understand the role of spatial and spectral variability of the natural biome. The samples were obtained from Etosha Pan, Namibia (19.20degS, 15.93degE, alt. 1100 m). It is shown how the BRDF depends on the measurement geometry - incident and scatter angles and on the sample particle sizes. As a demonstration of the application of the results, airborne BRDF measurements acquired with NASA's Cloud Absorption Radiometer (CAR) over the same general site where the regolith samples were collected are compared with the laboratory results. Good agreement between laboratory measured and field measured BRDF is reported.

In this study laboratory BRDF measurements of leaf samples are presented in an effort to understand the role of spatial and spectral variability of the natural biome. The samples measured in the laboratory included fresh and dry leaves from a poplar tree (Liriodendron tulipifera) and an acacia tree (Acacia greggii). Three different size samples were created: whole leaves, samples between 4 and 4.75 mm, and samples between 1.7 and 2 mm. The BRDF was measured at incident angles of 0deg and 67deg and at wavelengths of 340 nm, 470 nm and 870 nm. It is shown how the BRDF depends on the incident and scatter angles. The shapes of the BRDF curves strongly depend on the nature of the sample (i.e. crushed versus whole leaf). These laboratory results were compared with airborne measurements of BRDF from NASA's Cloud Absorption Radiometer (CAR) instrument.