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The composite infrared spectrometer (CIRS) instrument on board the Cassini Saturn orbiter employs two 1x10 HgCdTe detector arrays for mid-infrared remote sensing of Titan's and Saturn's atmospheres. In this paper we show that the real detector spatial response functions, as measured in ground testing before launch, differ significantly from idealized "boxcar" responses. We further show that neglecting this true spatial response function when modeling CIRS spectra can have a significant effect on interpretation of the data, especially in limb-sounding mode, which is frequently used for Titan science. This result has implications not just for CIRS data analysis but for other similar instrumental applications.

We describe the design, the development, and the calibration of a radiometer to measure water vapor abundance in the middle atmosphere, using the solar occultation technique from an orbiting platform. The use of gas cells containing water vapor and carbon dioxide leads to a relatively simple, but sensitive, design. This radiometer is shown to be capable of detecting water vapor in the mesosphere, where, because of dissociation by the Sun, the amounts are very small, of the order of 1 part per 10(6) or less. A flight version of the instrument will be launched in 1992 on board the European Retrievable Carrier space platform, and the data will be employed for a better understanding of the Earth's water budget.

The principles of remote sounding of vertical temperature profiles in planetary atmospheres containing cloud layers are presented for an approach that uses measurements at different angles to the local vertical to eliminate the unknown cloud effects. A numerical example for a model of the earth's atmosphere shows that soundings separated by 40 degrees in zenith angle permit the recovery of the temperature profile with an error that is not significantly greater than that obtained in the clear atmosphere case, and without serious horizontal smear. It is proposed that the method will be valuable for the interpretation of measurements made by instruments on spin-stabilized spacecraft on planetary missions, since in these cases the required angular coverage is obtained automatically for most trajectories.

An IR remote sensing instrument, similar in principle to some of those on terrestrial meteorological satellites, was flown to Venus on board the Pioneer Venus orbiter. Observations of the atmosphere were made from 5 December 1978 until 14 February 1979, during seventy-two orbits of the planet. The optical techniques employed and the design and implementation of the instrument are described.

The pressure-modulated CO(2) radiometer is a new kind of instrument capable of making temperature soundings in the 40-80-km region of the earth's atmosphere. It is intended to be mounted on a polar-orbiting satellite, where it will give global coverage of the upper atmosphere in a region that is not well understood at present but that is, as rocket soundings show, clearly the seat of many interesting and vigorous phenomena. The new technique employs a cell containing carbon dioxide as a filter. The pressure and hence transmission of this cell is periodically modulated, resulting in the selection of thermal radiation from the strong lines in the spectrum of atmospheric CO(2). This radiation originates at levels in the atmosphere where the pressure is low. The energy grasp of the device is large enough to give high sensitivity. Tests with a laboratory prototype and a balloon-borne instrument show that the device, if mounted outside the atmosphere, could detect changes of around 1 K in the temperature at 65-km altitude.