Hyperspectral imaging polarimeter (HIP) observations of ice clouds: data and modeling

In support of the RAMOS (Russian American Observation Satellites) program, an ongoing series of flights is being conducted using FISTA (Flying Infrared Signatures Technology Aircraft) which, in part, carries instruments to obtain polarization measurements of solar radiation scattered from clouds. Spectral polarization measurements have been made simultaneously across the 2.5-3.5 /spl mu/m region as a function of solar scattering angle using the Space Dynamics Laboratory's Hyperspectral imaging Polarimeter (HIP) instrument. The purpose of the experiment is to verify the expected strong sensitivity of polarization as a function of wavelengh within this spectral band, and to select the optimum wavelength for making remote diagnostic measurements of cloud compositions. There is also the complementary goal of studying polarization as a potential discriminator between naturally occurring solar-scatter backgrounds and man-made objects. Additional instrumentation onboard during these flights have indicated that the clouds present in these observations were composed primarily of ice rather than water. This paper is therefore focused on our efforts to model polarization due to solar scattering from non-spherical ice crystals. We describe the FISTA experiment, the HIP instrumentation, and the data processing methods used to derive the polarization data products. Finally, we present a simulation of the FISTA polarization experiment and compare these modeled results to the HIP data themselves.