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We describe joint U.S.-Russian Federation (RF) measurements of cloud scattering and polarization using the cloud chamber at Obninsk and field observations at Gorno-Altaysk. Cloud chamber experiments measure polarized scattering patterns of narrow distributions of ice crystals. These experiments may be supplemented with extended-range, intensity-only measurements. The U.S. team uses its scattering codes to verify intensity measurements involving oriented ice crystals, compares the orientation distributions with theory, and may field sensors to measure the total optical depth and the forward scattering properties of the particles in the cloud layer. Ice clouds present two serious impediments to electro-optical observation systems: clutter in short and mid-wave IR bands, and propagation loss when attempting to see through clouds. In high-altitude clouds, ice particles' mirror-like crystalline structure can produce intense "glint" features viewed from satellite sensors. Polarization can mitigate cloud clutter, since cloud-scattered sunlight is generally polarized, whereas point-source target signals are not. The effectiveness of polarization as a mitigant can in principle be modeled, but the models require validation, which must be based on carefully designed laboratory and field experiments.
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