A comparison of SMMR (Scanning Multichannel Microwave Radiometer) and airborne microwave measurements during GOASEX (Gulf of Alaska experiment)

The microwave brightness temperature (T sub B) of the open ocean was measured during September 1978 in a series of aircraft flights as part of the Gulf of Alaska Experiment (GOASEX). The purpose of GOASEX was to evaluate the performance of the remote sensors aboard SEASAT. One of the SEASAT sensors was the Scanning Multichannel Microwave Radiometer (SMMR), which measured the ocean T sub B at five microwave frequencies from 6.6 to 37 GHz. The NRL flights were performed to validate the SMMR microwave measurements. The aircraft measurements and the SMMR measurements were made at different but overlapping frequency ranges, and slightly different incidence angles. In order to compare the two sets of measurements, an estimate of the SMMR T sub B's at satellite altitude is derived from the aircraft measurements. Corrections for differences in altitude, frequency and incidence angle are made by the NRL Environmental Model, which is used to compute the atmospheric microwave parameters necessary for the correction based on the meteorological conditions at the time of the measurements. The results show that the SMMR T sub B's are in error at most frequencies, being generally smaller than the aircraft T sub B's. Biases which must be added to the SMMR T sub B's to bring them into agreement with the aircraft T sub B's are approximately the same as empirically derived biases from correcting the SMMR T sub B's prior to using them in geophysical algorithms.