Study On In-orbit Calibration Of HY-2B Satellite Radar Altimeter System Delay Based On Transponder

HY-2B satellite is the second marine dynamic environment satellite in China.Its radar altimeter,one of its main loads,undertakes the measurement of sea surface height(SSH),effective wave height and wind speed.In order to ensure the product quality of operational data of HY-2B satellite and the application in other fields,it is necessary to calibrate and verify the in orbit accuracy of HY-2B satellite radar altimeter.As an absolute calibration method,transponder has the advantages of good flexibility and high measurement accuracy.It has been successfully applied to the calibration of many satellite radar altimeters,including HY-2A radar altimeter,and has achieved good calibration results.In this thesis,the in orbit calibration experiment of HY-2B satellite radar altimeter is carried out based on the reconstructive transponder.(1)We have mastered the working principle of altimeter and transponder,the geometric relationship between satellite and earth,and the calibration experiment flow.From April to November 2019,vehicle transponders and supporting equipment have carried out on-board calibration experiments in many locations in the country,and obtained a large number of measured data.(2)Aiming at the improvement and innovation of HY-2A satellite ground signal matching method based on transponder,a more efficient,fast and accurate satellite ground signal matching method is proposed.Through the fluctuation of altimeter data caused by transponder in the process of transmitting signal,the corresponding relationship of satellite ground signal data characteristics is found.The new method simplifies the data processing flow,and greatly improves the calculation and processing efficiency.(3)In this thesis,the clock frequency deviation estimation method of HY-2A altimeter is improved,and a better method based on transponder is proposed.By comparing the time offset of parabola function of one-way or two-way path between satellite and transponder,the residual error of path correction in the original method is avoided,which affects the calculation result of clock frequency deviation.(4)The principle and method of delay calibration of altimeter system are clarified,the delay of transponder is corrected,the path delay such as troposphere delay above the zenith of transponder and ionosphere delay is deduced during the orbit calibration experiment.The precise coordinates of transponder are obtained by using the 8-hour observation data of static GPS and the high-precision GPS solution and processing through GAMIT / GLOBK software.Correction of altimeter measurement distance and the physical distance between the satellite and the earth.Calculate and measure the system delay of hy-2b altimeter,and verify the calibration results by cross calibration with jason-3.