Ultraviolet imaging polarimeter for observing polar mesospheric clouds

Abstract

Innovation Dr. Boulder, AB STRACT To study the polarization of sunlight scattered from Polar Mesospheric Clouds (PMC) and the Rayleigh scattering from the upper atmosphere, we designed, constructed, and flew an Ultraviolet Imaging Polarimeter (UVIP). A rocket-borne experiment, the UVIP consists of: an f/2 baffled telescope with a focal length of 76 mm; a filter/polarizer wheel with spectral bandpass and UV polarizing filters; a diode image intensifier, a thermoelectrically cooled, self-scanned diode array; and driver-interface electronics. The three polarization measurements are at 265 nm (8 nm spectral bandpass). Also, an unpolarized filter at 190 nm (20 nm bandpass) provides the color ratio 195 nm I 265 nm. The Earth's limb is imaged onto the 128 pixels of the detector, observing tangent heights of 40-1 50 km with a height resolution of 2 km. Previous optical measurements of PMC ice crystals indicate the particle scattering is Rayleigh-like, suggesting very high polarizations. To measure PMC against the ambient Rayleigh scatter requires 1 % precision in polarization. Since we accurately know the polarization of the Rayleigh background, the technique is self-calibrating. We present the design of this instrument and example data from two rocket flights.