IR/visible polarization measurements of scattered solar radiation from clouds

During 1997 and 1998 a series of flights were made using the FISTA aircraft which carried instruments to obtain polarization measurements of solar radiation scattered from clouds. Polarization measurements were simultaneously obtained at selected infrared and visible wavelength bands in an effort to differentiate between clouds of various compositions. An analysis of the 1997 data indicates that the degree of polarization from an apparently homogeneous deck of clouds can vary markedly at a given scattering angle. This can be caused by differences in the source of scene illumination, the spatial variability in scattering properties of the clouds, as well as wavelength-dependent contributions from scattering in the clear atmosphere above the cloud deck. While our observations generally resemble our expectations based on single-scattering theoretical models, future efforts to incorporate the observations made during the 1997 and 1998 FISTA flights and the effects of multiple scattering into these models are planned.