Profiling atmospheric water vapor with a K-band spectral radiometer

The vertical resolution of water vapor profiles from ground-based radiance measurements near the 22.235-GHz absorption line is analyzed. An information content analysis identifies four frequency channels that optimally resolve all of the linearly independent information available within this portion of the microwave spectrum for the retrieval of tropospheric water vapor by a K-band spectral radiometer (KSR) system. This instrument consists of 18 receivers operating at frequencies from 16-37 GHz, with spectral resolutions ranging from 50 MHz to 1 GHz. Parallel measurement of 18 atmospheric brightness temperatures allows for high temporal resolution of both integrated and profiled water vapor dynamics. Inversion of the radiance spectrum is accomplished using a minimum variance estimation technique that is analyzed for its resolution and error properties. Water vapor profiles derived from radiometric observations made by the KSR system are presented and shown to be in good agreement with coincident radiosonde measurements and lidar retrievals