Microwave methods of atmospheric temperature and water vapor profiling

Abstract

A temperature profiling radiometer based on a highly stable synthesizer, rather than traditionally used Gunn oscillators, has been designed and fabricated under contract to White Sands Missile Range. This profiler is capable of tuning a user-selected ensemble of frequencies in the range of 52.85 to 58.8 GHz as well as fixed water vapor and water channels at 25.8 and 31.4 GHz. This instrument weighs about 30 kg and consumes about 200 watts. Because of the frequency stability of the receiver, and because of the large number of observing frequencies possible, improved profile accuracy and resolution is expected over Gunn-based temperature profilers. An inexpensive, simple, and accurate calibration target system that includes the antenna system has been developed for this profiler. The calibration target can be loaded with liquid nitrogen or other cryogenic liquids. Tests with a Radiometrics water vapor radiometer have demonstrated stability of 0.1 K over 6 hours. The cryogenic liquid temperature can be known by its boiling point to within several hundredths of a Kelvin by a simple barometric pressure measurement. Preliminary design work has also been accomplished on a portable (35 kg) water vapor profiling radiometer. This radiometer is to utilize a stable synthesizer to map pressure broadening by tuning across the 22 GHz water vapor line.<>