Comparison of water vapor measurements by microwave radiometers and Raman lidar

In November-December 1991, a substantial number of remote sensor and in situ instruments were operated together in Coffeyville, Kansas, USA, during the climate experiment FIRE II. Included in the suite of instruments were (a) the NOAA Environmental Technology Laboratory's three-channel microwave radiometer (20.6, 31.65, and 90.0 GHz); (b) the NASA/GSFC Raman lidar; and (c) frequent research-quality CLASS radiosondes. The Raman lidar operated only at night and the focus of this portion of the experiment concentrated on clear conditions. The temporal resolution of the Raman lidar was 1 min, the spatial resolution was 75 m, and the upper range of the lidar was about 8.5 km. The lidar data, together with frequent radiosondes and measurements of temperature profiles (every 15 min) by a Radio Acoustic Sounding System (RASS), allowed profiles of temperature and absolute humidity to be estimated every minute. The authors first present results comparing measurements and calculations of microwave brightness temperature based on three contemporary absorption models. Then, they show comparisons of precipitable water vapor measurements at two-min temporal scales between the two instruments. The results clearly demonstrate the potential of simultaneous operation of radiometers and Raman lidars for fundamental physical studies of water vapor and radiative transfer. >