Digital-correlation Full-polarimetric Microwave Radiometer Temperature Control System Design And Calibration Analysis

As a new type of passive microwave remote sensor developed since 1990 s for measuring ocean wind vector, full-polarimetric microwave radiometer(FPMR) can measure 4 Stokes parameters(i.e., vT,hT,3T and4T), and this is beneficial for studying the radiative characteristics of the target, since the traditional microwave radiometer can only measure parameters vT andhT. Usually, FPMR is totally calibrated by using a full-polarimetric calibrator(FPCAL). During the calibration, the stability of FPMR will affect the cycle and results of the calibration. As the temperature fluctuation is a key factor which effects the stability of FPMR, the stability of the temperature in this system is very important.This paper presents the theories of the characteristics of system noise, the accuracy of measurement and the sensitivity of the FPMR to point out the influence of temperature on the system stability. Then in order to analyze the effect of the temperature on the calibration cycle, the theory and design of the 23.8GHz digital-correlation full-polarimetric microwave radiometer(DPMR) are introduced, the principle of FPCAL is expounded, and the calibration mechanism of five points calibration method is described. The results of above analysis show the necessity of the temperature control for the radiometer.To fulfill the requirements of temperature control for microwave radiometer, a temperature control system is designed according to the principle of semiconductor refrigeration. The hardware of this system is designed by using the high precision platinum resistance and microcontroller, and the software is based on the Fuzzy PID algorithm. The result of temperature control experiments show that the control precision is better than 0.1K, which make the radiometer work in a constant temperature state for a long time.Finally, based on the DPMR, the FPCAL and the temperature control system, two calibration experiments are completed. In the first calibration experiment, the microwave radiometer is working under constant temperature condition, and in the second time, it is working without temperature control. The analysis of experimental data under different states shows that maintaining the DPMR’s temperature steady can improve the stability and calibration precision of the system. In the five points calibration, the measurements viewing FPCAL at five angles and outside blackbody at ambient temperature are used to calculate calibration coefficients. Maintaining the DPMR’s temperature steady can keep the radiometer system stable in five point measurement cycle, and this cycle can be extended to seven points, which is about eight to ten minutes. The above results validate the importance of the temperature control scheme for the microwave radiometer system. At last, the next research direction is put forward.