Research On Calibration Method Of HY-2B Altimeter Based On Field Observation

It has been more than 50 years since the spaceborne radar altimeter was proposed and developed.It has now become an important tool for marine research and climate change research.The detection of sea surface dynamic parameters through satellites is an important way to obtain ocean data on a large scale,and the altimeter is a relatively developed one of the spaceborne microwave sensors.The altimeter can obtain important sea surface dynamic parameters such as current,wave,tide,and sea surface wind speed by measuring the sea surface height,significant wave height,and backscatter at the same time.These dynamic parameters can be applied to marine disaster prevention and mitigation,marine resource development and climate change research et al.The altimeter is a high-precisionmicrowave radar.During the observation of the sea surface height,significant wave height,and backscatter,it will be subject to such corrections as instrument correction,orbit correction,tropospheric correction,ionospheric correction,sea state bias and geophysical corrctions.If there is no strict error correction and calibration,it will seriously affect the accuracy of the altimeter.Only by modifying these influencing factors can we better perform altimeter calibration and obtain more accurate calibration parameters.As the accuracy requirements of the altimeter continue to increase,countries have continuously built an altimeter calibration site based on the calibration requirements of the altimeter.China’s HY-2B satellite was launched in October 2018,and China also conducted a HY-2B altimeter calibration test in Wanshan,Zhuhai,and initially performed a HY-2B altimeter calibration.The inspection work also laid the foundation for the long-term operation of Wanshan calibration site in the future.The absolute calibration of the altimeter is a complicated process.This thesis starts with the history and development of the altimeter and calibration site,with a briefly introduces of the current status of the four international calibration sites and the Zhuhai Wanshan calibration site.The principle of altimeter height measurement and the influencing factors of altimeter distance measurement are discussed in detail.Then use this as a starting point to conduct in-depth research on the HY-2B altimeter calibration,including absolute calibration based on the observation data of the Wanshan calibration field and star cross calibration based on the Jason-3 observation results.The bidding compares the differences between the various influencing factors in detail,and provides certain technical support for the HY-2B absolute calibration.The specific research work and innovations are as follows:1)At present,there are few absolute calibration tests for HY-2B.In this thesis,the absolute calibration tests are carried out in Wanshan calibration site.The tests are based on GPS base stations and coastal tide gauges.A calibration test for tide gauges from November 3,2018 to December 12,2018,was carried out near the sub-satellite point of pass 375.A total of three coastal tide gauges were deployed,two of which were used to measure sea surface height.During this period,HY-2B revisited the calibration field three times,and the three calibration results showed that the calibration results of the two tide gauges are the same.There are certain HY-2B calibration bias obtained during the three cycles.The calibration bias are-0.31 ± 0.14 m,-0.27 ± 0.04 m,and-0.27 ± 0.001 m,respectively.The result came from the HY-2B calibration test phase,and it is necessary to carry out long-term calibration work in order to obtain more stable calibration parameters.2)In addition to the coastal tide gauge,this thesis also used the GPS buoy placed directly at the sub-satellite point of the calibration field in Wanshan,Zhuhai on November 12,2018 for calibration.The results of this calibration show that the difference between the calibration results based on GPS buoys and the calibration results based on the coastal tide gauge buoys at the same time is quite large,about-0.0766±0.2031 m.Because the GPS buoy test data is less,only one orbit of a cycle,and unlike the tide gauge,the GPS buoy is measured as a descending pass,so the results are quite different from the tide gauge results.The comparison of the HY-2B error corrections between the descending pass and associated pass in this thesis also confirms that there is a big difference.At present,obtaining more accurate HY-2B calibration parameters based on GPS buoys still requires data support for long-term operational operation of GPS buoys.3)This thesis cross-calibrates the intersection of stars in the four revisit cycles of Jason-3 between November 2018 and mid-December 2018 between HY-2B and Jason-3.The calibration results show that:(1)HY-2B and Jason-3 are close in SSH measurement,and the overall cross-calibration bias is 0.025 m.(2)In addition to the SSH measurement,this thesis compares the ranging error correction obtained by the L2 products of HY-2B and Jason-3.The comparison results show that the maximum error in the error corrections is the ionospheric correction error with the RMSE of 0.045.The overall HY-2B and Jason-3 altimetry results are not much different.The HY-2B altimetry results are close to the other international altimeter.