WINDII, the wind imaging interferometer on the Upper Atmosphere Research Satellite

The WIND imaging interferometer (WINDII) was launched on the Upper Atmosphere Research Satellite (UARS) on September 12, 1991. This joint project, sponsored by the Canadian Space Agency and the French Centre National d'Etudes Spatiales, in collaboration with NASA, has the responsibility of measuring the global wind pattern at the top of the altitude range covered by UARS. WINDII measures wind, temperature, and emission rate over the altitude range 80 to 300 km by using the visible region airglow emission from these altitudes as a target and employing optical Doppler interferometry to measure the small wavelength shifts of the narrow atomic and molecular airglow emission lines induced by the bulk velocity of the atmosphere carrying the emitting species. The instrument used is an all‐glass field‐widened achromatically and thermally compensated phase‐stepping Michelson interferometer, along with a bare CCD detector that images the airglow limb through the interferometer. A sequence of phase‐stepped images is processed to derive the wind velocity for two orthogonal view directions, yielding the vector horizontal wind. The process of data analysis, including the inversion of apparent quantities to vertical profiles, is described.