A compact airborne G-band (183 GHz) water Vapor Radiometer and retrievals of liquid cloud parameters from coincident radiometer and millimeter wave radar measurements

Abstract

ProSensing Inc. has developed a G-band (183 GHz, 1.5 mm wavelength) water Vapor Radiometer (GVR) for measuring low concentrations of atmospheric water vapor and liquid water. Using four double sideband receiver channels, the instrument measures brightness temperature at 183.31 +-1, +-3, +-7 and +-14 GHz . An airborne version of the instrument, packaged and wired to operate from a standard PMS probe canister, was successfully tested onboard the National Research Council of Canada Convair-580 aircraft during the Canadian CloudSat and CALIPSO validation flights (C3VP) through the winter of 2006-07. The Zenith G-band radiometer brightness temperature data collected with the GVR were complemented with co-located cloud reflectivity measurements with the NRC W and X-band (NAWX) radar system and in situ probes. By flying the aircraft in a stepped and porpoising ascent/descent patterns, liquid cloud water content was estimated from the GVR retrieved liquid water path. The effective radius and number density of liquid clouds were then estimated by combining the liquid water content with the W-band radar reflectivity factor (Z) and by applying a small correction factor, based on the characteristic drop size distribution shape of the observed cloud.