The evaluation of the direct and indirect aerosol forcings of climate requires precise knowledge of the aerosol optical thickness, size distribution, chemical composition, and number density. Global monitoring of these parameters from satellites requires instruments that make full use of the information content of the scattered solar radiation. In this paper we analyze multispectral and multiangle photopolarimetric observations performed with an airborne version of the Earth Observing Scanning Polarimeter over the ocean and demonstrate their exceptional retrieval potential. Using the 0.865- and 2.250-&mgr;m channels, we are able to determine the parameters of a bimodal size distribution, identify the presence of water-soluble and sea salt particles, and retrieve the optical thickness and column number density of aerosols. We also demonstrate that less comprehensive measurements by existing instruments would fail to provide retrievals of comparable completeness and accuracy. ¿ 2001 American Geophysical Union