增益对星载微波辐射计系统线性度的影响分析

针对星载微波辐射计中检波器的工作特性进行分析. 观测固定目标时, 通过调节AGC (Automatic Gain Control)的大小, 定量分析系统伏安特性曲线, 对星载微波辐射计系统线性度进行定性分析. 结果表明, 通过调节AGC大小, 系统增益发生变化, 导致检波器工作区间发生微弱变化, 通过两点定标不能完全消除由于增益引起的非线性误差. 对一定亮温范围的观测目标进行分析, 结果证明, AGC变化时反算亮温与实际目标亮温差值随观测亮温的变化而成非线性变化. 从而证明, 系统增益变化导致的亮温变化通过两点线性定标并不能完全消除. 在系统正常工作或实时定标过程中, 要尽量避免调节AGC值, 保证微波辐射计系统工作在线性区间.

Analysis of the System Linearity Caused by Gain Variation of Satellite-borne Microwave Radiometer

The characteristics analysis of diode detector of satellite-borne microwave radiometer has been described.In this paper,given a certain observation target,the retrieved brightness temperatures changed correspondingly with the different values of system Automatic Gain Control(AGC). By adjusting the system gain,a little change happened for detector working range.The variation caused by nonlinearity of diode can not be completely eliminated by using two-point calibration method.The brightness temperatures retrieved in this paper are in a wide range of 3～350K.The experimental results demonstrate that there is obvious nonlinearity for brightness temperatures between retrievals minus actual values and observing values,which can not be eliminated by using two-point calibration.So,in the process of working and real-time calibration,the system must be assured working in approximately linear working range with a certain AGC value as possible.