Comparison of the Effects of Different Microwave Channel Combinations and TB Functions in the Algorithm for Retrieving Precipitable Water in the Clear Atmosphere
空基微波辐射计遥感晴天大气可降水量：不同通道组合和亮温函数形式的效果的比较分析

For remote sensing of atmospheric precipitable water (P W) over the oceans, a number of retrieval regression algorithms have been developed with different microwave channel combinations and different function forms of brightness temperature (T B). The objective of this work is to compare and examine the effects of different channel combinations and different function forms of T B with three simulated T B data sample sets, corresponding to high, medium, and low mean values of P W. The successive regression analysis indicates that: (1) the optimum dual or triple channel combination is different for different variation range of P W; (2) the channel 22.235 GHz is not suitable for measuring high total water vapor amount with large variation range, so the triple channel combination (19, 22, 37 GHz) used by SSM/I is not very ideal for the global retrieval of P W; (3) it is necessary to establish the climate zonally or seasonally divided retrieval algorithm because it has smaller regression residual error; (4) the function form ln(280-T B) generally gives better regression and retrieval results than the linear form of T B, but it is not true for 22.235 GHz; and (5) the use of the term T 2 B 22 can improve the regression as well as retrieval results in the case of low and medium values of P W.