Abstract

A new instrumental approach to measurements of upper atmospheric winds is being developed for the upcoming NASA EOS spacecraft. This new approach uses electrooptic phase modulation of atmospheric infrared emission, together with a reference gas cell, to measure wind-induced Doppler shifts by spectral correlation. A single crystal of cadmium telluride (CdTe) to which an oscillating electric field is applied serves as the electrooptic phase modulator (EOPM). Infrared radiation passed through the crystal is phase modulated at the frequency of the applied electric field which places sidebands on each emission line of the atmospheric spectrum. Doppler shifts are measured by determining the modulation frequency that causes the atmospheric emission sidebands to reestablish correlation with the absorption lines of the gas contained in the reference cell. In this paper we focus on recent laboratory measurements which examine the characteristics of CdTe EOPMs operating near 8 μm and at modulation frequencies near 100 MHz. The laboratory work simulates the measurement of the concentration of N₂O in an atmospheric limb path. N₂O is of particular interest because it is the tracer species of choice for wind measurements in the 20–50-km altitude range. The measurements have also been used to verify the numerical models we have developed to compute the transfer function of the instrument and to predict the performance of a spaceborne sensor in measuring winds, species abundances, and atmospheric temperature and pressure.

© 1986 Optical Society of America