Calibration Precision Analysis For Spaceborne Microwave Radiometer

Spaceborne microwave radiometer is nowadays one of the most important means in earth observation and space exploration. It plays an important role in the remote sensing application because of its all-day, all-weather observation capability for earth surface observation and atmospheric sounding. Calibration is the basis of quantitative application, and calibration precision is the integrated result of several instrument performances, such as sensitivity, stability and so on. As a result, it is important to analyze the effects of the concerned factors which affect the calibration precision. Calibrating a spaceborne radiometer is usually implemented with two different methods. One is usually for the radiometers with scanning mechanism, where the receiving antenna looks at the earth surface, a cold and a hot reference target periodically, and the"two-point calibration"is implemented by the data from the cold and hot references. The other one is for the radiometers with fixed looking direction (usually nadir looking), where receiver is switched periodically to the observation antenna, the calibration antenna looking at the cold sky and an internal matched load termination with precise temperature, and the"two-point calibration"is implemented by the data from the cold sky and internal matched load as the cold and hot references. The calibration equation and calibration algorithm of this method is more complicated than the former one. So this paper I pay specially attention on analyzing calibration precision of the spaceborne microwave radiometer using the latter method.In this paper, the process of the calibration and set up calibration equation are described. Based on the calibration equation, the error sources contributed to the calibration accuracy, which include the forward transmission network before receiver, linearity and sensitivity of the receiver, and the A/D error are found. The result can not only be used for instructing how to analyze the calibration precision, but also suggesting on the design of a spaceborne microwave radiometer with the rule of the influence of the transmission network.