Wednesday, 12 February 2003
Change of the brightness temeprature in the microwave region due to the relative wind direction
The microwave brightness temperature (MBT) measured by Special Sensor Microwave / Imager (SSM/I) on Defense Meteorological Satellite Program (DMSP) is compared with the collocated vector wind measured by SeaWinds on QuikSCAT at each wind vector cell (wvc). The number of the collocated cells is over 1.0x105 in a month. Because of the orbital difference between these satellites, the collocated data is partially located. We should pay attention to this problem until ADEOS II, which has both the microwave imager and the scatterometer, is to be launched. The collocated data set is divided into groups according to range of SST, water vapor and liquid water content, and used to extract the change of the MBT due to the wind direction relative to the microwave radiometer. The change of the MBT due to the relative wind direction has not been considered in the algorithm of the wind speed retrieval and may cause the significant error in the estimation. In each category, the mean rates of change of the MBT to geophysical parameters are evaluated by the singular value decomposition. Besides the difference between the cross-wind and the along-wind conditions, the analysis showed that the MBT can be higher by 2 to 4 Kelvin when the ocean wind blows toward the same direction with the radiometer than it blows against the radiometer. In addition, we try the rough estimation of the change of the MBT according to the relative wind direction on the wvc without information of the in situ wind direction, using the knowledge of the average rates of the MBT to the geophysical parameters.