An airborne polarimeter for atmospheric radiation studies

Abstract

A new polarimeter, to measure the Stokes parameters of linearly polarized atmospheric visible radiation in four narrow spectral regions, is described. The instrument was developed for airborne application to measure polarization of reflected solar radiation from various land, sea and cloud surfaces. It consists essentially of a polarizing prism assembly of four Glan Thompson prisms oriented so as to transmit light vibrations at 0°, 45°, 90° and 135° with respect to a chosen direction. A rotating aperture wheel allows the light beams transmitted by the polarizers to reach the cathode of a photomultiplier tube in sequence. The signals from the photomultiplier tube are separated and identified with gate circuits triggered by pulses from magnetic transducers fixed near the polarizing prisms. From simple relations between the output signals the desired Stokes parameters are obtained. The transducer pulses are also passed through delay circuits to give delayed pulses to gate housekeeping data such as spectral region, optical gain, scan angle, etc. The method of measurement and some results obtained during a recent meteorological expedition are presented.