Intercomparisons of wind speed measurements derived from ERS-1 scatterometer and altimeter and SSM/I over the tropical Atlantic Ocean

Since July 1987 the Special Sensor Microwave Imagers (SSM/I) on satellites in the U.S. Defense Meteorological Satellite Program provide surface wind speed computed from the measurements of the intensity of microwave radiation emitted from the ocean surface. The scatterometer and the altimeter of the European Remote Sensing Satellite (ERS-1) collect global measurements of sea surface winds. The three instruments use empirical models, which have been independently verified, to estimate wind speed in oceanic regions with an accuracy better than 2 m/s. Comparisons are made of scatterometer and altimeter, and of scatterometer and SSM/I wind speed measurements from the Atlantic tropical area during November 1992. The rms values of the differences between scatterometer and altimeter, and between scatterometer and SSM/I are 1.58 m/s and 1.48 m/s, respectively. There is no global bias between scatterometer and SSM/I wind estimates, but between scatterometer and altimeter wind speeds the bias is about 0.84 m/s. In order to assess the cause of the differences, comparisons are made in different environmental conditions. For instance the difference between the scatterometer and altimeter appears to be dependent on the significant wave height and the difference between scatterometer and SSM/I is dependent of the integrated water vapour content