Sensitive Broadband Receivers for Microwave Limb Sounding

− We present the measured performance of a sensitive new broadband receiver developed for a future microwave limb sounding instrument to map chemical species in the upper troposphere. This receiver will downconvert thermal emission spectra in the 180-280 GHz band using superconductor-insulator-superconductor (SIS) heterodyne mixers. The high spectral resolution achieved with heterodyne detection enables precision measurement of the profiles of pressure-broadened lines. Broad instantaneous bandwidth (24 GHz for a single mixer) enables multiple species to be measured simultaneously. The high sensitivity of this receiver and resulting short integration times, when combined with a novel optical configuration, will enable rapid horizontal and vertical scanning of the limb, resulting in three-dimensional maps of a large number of key chemical species in the trophosphere measured five to nine times per day over nearly the entire planet.