Estimate of the aerosol properties over the ocean with POLDER

J. L. Deuzé, P. Goloub, M. Herman, A. Marchand, G. Perry, S. Susana, D. Tanré
2000 Journal of Geophysical Research  
The wide field of view imaging spectroradiometer Polarization and Directionality of the Earth's Reflectance (POLDER) developed by Centre National d'Etudes Spatiales and operated aboard the Japanese heliosynchronous platform Advanced Earth Observation Satellite (ADEOS) from October 30, 1996, to June 30, 1997, provided the first global systematic measurements of the spectral, directional, and polarized characteristics of the solar radiation reflected by the Earth/atmosphere system. These original
more » ... observational capabilities offer an opportunity to enhance the characterization of several components of the global environment, especially the oceanic and terrestrial vegetal primary production, the aerosol physical and optical properties, and the tridimensional structure and microphysics of clouds. Here we examine the remote soensing of aerosols over the oceans. In a first step the aerosol optical thickness and Angstr6m exponent are derived from the radiance measurements. In a second step the polarization measurements are used for the retrieval of the aerosol refractive index. The inversion algorithm assumes spherical, nonabsorbing particles with monomodal lognormal size distribution. The adequacy of this modeling is discussed for a representative set of aerosol observations. Successful retrieval is generally achieved in the presence of small aerosols with 3,ngstr6m exponent larger than -1.0. For suchoParticles, polarization may provide information on the particle refractive index. As the Angstr6m exponent of the particle decreases, the data fitting residual errors increase, especially in polarized light, which prevents the retrieval of the aerosol refractive index. The trends of the discrepancies point out two shortcomings of the aerosol modeling. The theoretical results systematically underestimate the contribution of small polarizing particles in the polarization measurements for side-scattering angles ranging from 80 ø to 120 ø . This indicates very probably that aerosol models have to follow bimodal size distribution. On the other hand, the systematic trend of the directional behavior of the upward radiance and the lack of significant rainbow effect in the measurements result probably from nonsphericity of some large aerosols. Confirmation of these points requires improved analysis of the POLDER data. 15,329 15,330 DEUZ}2 ET AL.' AEROSOLS OVER OCEANS WITH POLDER The wide field of view imaging spectroradiometer POLDER performs multispectral observations of the directionality and polarization of the solar radiation reflected by the Earth. Wide field of view optics and a matrix array detector provide both along-and cross-track viewing directions, so that the same terrestrial target can be observed from different viewing geometries during the same orbit. A rotating filter wheel provides radiance measurements in nine channels, ranging from 443 to 910 rim. Moreover, the channels centered at 443, 670, and 865 nm are equipped with polaroids, which permits measurements of the polarized light [Deschamps et al., 1994] . These unique capabilities are expected to allow better characterization of different geophysical parameters concerning the terrestrial biosphere, the cloud radiative impact, and the ocean color. Particularly, they should offer new possibilities for characterizing the terrestrial aerosols from space. POLDER was operating successfully aboard ADEOS from
doi:10.1029/2000jd900148 fatcat:3bssrpxpencf7dzh4lkiw4deb4