Abstract

The current operational atmospheric temperature and moisture sounders are unable to meet the requirements of weather forecasting community mainly because of the insufficient vertical resolution and cloud contamination effects. There is also a strong requirement for a detailed definition of the atmospheric temperature profile in the stratosphere. There are several reasons for this requirement. First, a better knowledge of the stratospheric temperature profile will help the retrieval of the tropospheric temperature profile which is essential for weather forecasting; secondly, stratospheric chemistry and global ozone studies require an accurate determination of the chemical reaction rates which are temperature dependent. But up to now, the stratospheric requirement has not been met by previous or planned instruments mainly because of their low spectral resolutions. Conventional infrared spectrometers or filter radiometers in the nadir sounding mode can give broad weighting functions in the middle and lower stratosphere, but nothing higher. Furthermore, the energy available in any sufficiently small spectral interval would be so small as to require long observation time, which is generally not allowed in a polar satellite. The limitation in vertical resolution is caused mainly by the broadness of the contribution functions of the current instruments which is due partly to their low spectral resolution. One way to decrease the width of the contribution functions and improve the vertical resolution is to use instruments of higher spectral resolution, which are able to resolve the individual spectral lines. There are several techniques to achieve high spectral resolution sounding, including large grating and the Fourier transform interferometer. One of the attractive approach is to use the rugged, high resolution Fabry-Perot etalon. The Multiorder Etalon Sounder (MOES), as a combination of etalon and the newly invented circle to line converter,¹ compares very favorably to other spaceborne optical instruments in terms of performance versus complexity.

© 1991 Optical Society of America