MILLIMETER-WAVE RADIOMETRIC OBSERVATIONS OF THE TROPOSPHERE - A COMPARISON OF MEASUREMENTS AND CALCULATIONS BASED ON RADIOSONDE AND RAMAN LIDAR

A comparison of clear-air brightness temperatures is performed between radiometric measurements and atmospheric radiative transfer calculati ons. The measurements were made using the NASA Goddard Space Flight Ce nter's Millimeterwave Imaging Radiometer (MIR) in a series of airborne and ground-based atmospheric experiments at six millimeter-wave frequ encies: 89; 150; 183.3 +/- 1 +/-3, +/-7; and 220 GHz, With the inclusi on of the 220 GHz channel, these measurements are the first passive ob servations of the atmosphere made simultaneously at the six frequencie s, The MIR was operated concurrently with supporting meteorological in struments (radiosonde and Raman lidar) to construct a paired set of bo th spatially and temporally coincident calibrated brightness temperatu res and atmospheric profile parameters, Calculated brightness temperat ures based on the measured atmospheric profile parameters were obtaine d using a numerical radiative transfer model, Incremental water-vapor weighting functions were used to study the impact of radiosonde hygrom eter errors on the radiative transfer calculations, The aircraft-based brightness temperature comparisons are generally within 3 degrees K f or the channels sensitive to the lower atmospheric levels (89, 150, 18 3.3 +/-7, and 220 GHz), but show discrepancies of up to 11 degrees K f or the opaque channels (183.3 +/-1, and +/-3 GHz) caused primarily by radiosonde bias, The ground-based calculations are similarly found to be sensitive to hygrometer errors in the lower atmosphere, Ground-base d comparisons between MIR observations and lidar-based calculations ar e typically within +/-6 degrees K.