Radiometer Calibration For Brightness Temperature Inversion

As a result of the fact that microwave can penetrate through smoke, fog, clouds and it has the capability of working all-weather and all time, microwave radiometer has established itself in a wide range of applications and it has received considerable attention in the scope of worldwide. Calibration plays an important role in the application of microwave radiometer, and the calibration precision exerts profound impacts upon the absolute precision during the measurement. Hence, the methods of improving the precision of calibration need further investigation.The approaches of improving the measurement precision of radiation temperature for shooting range are discussed in this paper, and then different calibration schemes corresponding to different types of radiometers are also given. In addition, several critical questions related with the calibration target are analyzed, and the factors which influence the system sensitivity and the precision of calibration target are investigated.According to the specific requirements put forward by the radiation temperature measurement system for shooting range, the high-precision calibration scheme of radiometer is demonstrated. Firstly, both the choice of radiometer and the design of calibration target are carried out. And then the high-precision calibration scheme of receiver is adopted in this paper, in addition it is proved that radiometer has significant linearity. Moreover, the calibration scheme is outlined on the basis of the characteristics of radiometry for shooting range. The fact that the inverse-noise seriously affects the calibration precision is analyzed, and the method of decreasing the inverse-noise by employing circulator is discussed. Furthermore, both the new formula of radiation temperature for calibration target and the new equation of calibration are derived when the non ideality of blackbody, the influence to brightness temperature imposed by insulating layer of calibration target and the brightness temperature received by antenna when the inverse-noise is reflected. The precision of the calibration equation is also analyzed, and the experiment result demonstrates that the calibration precision is improved and meets the requirement of the system.