The validation of microwave spaceborne observations by surface-based remote sensors

Abstract

Passive microwave observations from polar-orbiting satellites provide meteorologically important information on temperature profile, water vapor, and cloud liquid water, The variable measured by radiometers in radiance, or brightness temperatures, as a function of frequency, viewing angle, and polarization. Meteorological parameters are then extracted from the radiance measurements by retrieval algorithms. The utility of these parameters, both in operational meteorology and in monitoring climate change, depends on the calibration and stability of the instrument, and on the type of retrieval algorithm that is used. Utimately, the derived parameters must be compared with ground truth. For temperature and water vapor soundings, radiosondes are frequently used for validation and calibration. However, for the climatologically important variable cloud liquid water, conventional measurements are not adequate, and surface- and aircraft-based remote sensor measurements are required. In this paper, calibration of microwave instruments is discussed and comparisons with various sources of ground truth are presented. In addition, a possible role for surface-based remote sounders in the calibration and validation of satellite products is suggested. These remote sounders include microwave radiometers, wind profilers, and Radio Acoustic Sounding Systems (RASS).