A polarizing Michelson interferometer for measuring thermospheric winds

Abstract

The polarizing atmospheric Michelson interferometer (PAMI), a new version of the wide-angle Michelson interferometer, is used to measure winds in the thermosphere from the Doppler shifts of atomic oxygen airglow emission. In the polarizing instrument, the optical path difference is changed simply by rotating a polarizer external to the interferometer. This allows a very simple scanning mechanism, and makes the interferometer very stable against vibration. The PAMI's general behaviour has been modelled in terms of Muller matrices, providing a framework for the analysis of partial polarization states within the Michelson interferometer. A field instrument based on the above concept was designed, built and operated in the field. PAMI is similar to other Michelson interferometers that measure thermospheric winds and temperatures, retaining the benefits of high light throughput, while offering advantages including lower cost, simplicity and portability. PAMI was constructed from readily available components, wherever possible, to facilitate replacement. The instrument is highly sensitive and thus is designed to be used for field measurements at locations far from city lights. Results from the AIDA observation campaign in Puerto Rico (17 degrees 57'0"N, 66 degrees 52'42"W), where coordinated observations were made using the PAMI together with other optical and radio measurements during April and May 1989, are presented.