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| 1 | Absolute calibration of HY-2A and Jason-2 altimeters for sea surface height using GPS buoy in Qinglan, China显示文摘GPS buoy methodology is one of the main calibration methodologies for altimeter sea surface height calibration. This study introduces the results of the Qinglan calibration campaign for the HY-2A and Jason-2 altimeters. It took place in two time slices;one was from August to September 2014, and the other was in July 2015. One GPS buoy and two GPS reference stations were used in this campaign. The GPS data were processed using the real-time kinematic (RTK) technique. The fi nal error budget estimate when measuring the sea surface height (SSH) with a GPS buoy was better than 3.5 cm. Using the GPS buoy, the altimeter bias estimate was about -2.3 cm for the Jason-2 Geophysical Data Record (GDR) Version ‘D' and from -53.5 cm to -75.6 cm for the HY-2A Interim Geophysical Data Record (IGDR). The bias estimates for Jason-2 GDR-D are similar to the estimates from dedicated calibration sites such as the Harvest Platform, the Crete Site and the Bass Strait site. The bias estimates for HY-2A IGDR agree well with the results from the Crete calibration site. The results for the HY-2A altimeter bias estimated by the GPS buoy were verifi ed by cross-calibration, and they agreed well with the results from the global analysis method. | CHEN Chuntao ZHU Jianhua ZHAI Wanlin YAN Longhao ZHAO Yili HUANG Xiaoqi YANG Weiwei | 2019 | Journal of Oceanology and Limnology2019,37,5: | 5 |
| 2 | An improved method of absolute calibration to satellite altimeter: A case study in the Yellow Sea, China显示文摘An improved absolute calibration technology based on indirect measurements was developed through two probative experiments, the performance of which was evaluated by applying the approach to in situ sea surface height(SSH) at the Tianheng Island(tidal gauge) and the satellite nadir(GPS buoy). Using Geoid/MSS(mean sea surface) data, which accounted for a constant offset between nadir and onshore tidal gauge water levels, and TMD(tidal model driver), which canceled out the time-varying offsets, nadir SSH(sea surface height) could be indirectly acquired at an onshore tidal gauge instead of from direct offshore observation. The approach extrapolated the onshore SSH out to the offshore nadir with an accuracy of(1.88±0.20) cm and a standard deviation of 3.3 cm, which suggested that the approach presented was feasible in absolute altimeter calibration/validation(Cal/Val), and the approach enormously facilitated the obtaining SSH from the offshore nadir. | LIU Yalong TANG Junwu ZHU Jianhua LIN Mingsen ZHAI Wanlin CHEN Chuntao | 2014 | Acta Oceanologica Sinica2014,33,5: | 3 |
| 3 | Preliminary calibration results of the HY-2B altimeter’s SSH at China’s Wanshan calibration site显示文摘Satellite altimeter needs to be calibrated to evaluate the accuracy of sea surface height data.The dedicated altimeter calibration field needs to establish a special calibration strategy and needs to evaluate its calibration ability.This paper describes absolute calibration of HY-2 B altimeter SSH using the GPS calibration method at the newly Wanshan calibration site,located in the Wanshan Islands,China.There are two HY-2 B altimeter passes across the Wanshan calibration site.Pass No.362 is descending and the ground track passes the east of Dan’gan Island.Pass No.375 is ascending and crosses the Zhiwan Island.The GPS data processing strategy of Wanshan calibration site was established and the accuracy of GPS calibration method of Wanshan calibration site was evaluated.Meanwhile,the processing strategies of the HY-2 B altimeter for the Wanshan calibration site were established,and a dedicated geoid model data were used to benefit the calibration accuracy.The time-averaged HY-2 B altimeter bias was approximately 2.12 cm with a standard deviation of 2.08 cm.The performance of the HY-2 B correction microwave radiometer was also evaluated in terms of the wet troposphere path delay and showed a mean difference-0.2 cm with a 1.4 cm standard deviation with respect to the in situ GPS radiosonde. | Chuntao Chen Jianhua Zhu Chaofei Ma Mingsen Lin Longhao Yan Xiaoqi Huang Wanlin Zhai Bo Mu Yongjun Jia | 2021 | Acta Oceanologica Sinica2021,40,5: | 2 |
| 4 | Preliminary calibration results for Jason-3 and Sentinel-3 altimeters in the Wanshan Islands显示文摘We present preliminary calibration results for Jason-3 and Sentinel-3A altimeters that we set up in the Wanshan Islands in Guandong Province,China.Two campaigns were carried out in 2018,from March 8 to April 16 and from November 3 to December 11,2018.Three GPS reference stations and tide gauges were established on the islands of Zhiwan,Dangan,and Wailingding during the campaigns.The in-situ sea surface height(SSH)of the altimeter footprint was determined using the tide gauge.The tidal and geoid connection between the tide gauge locations and the altimeter footprints were computed with the NAO.99Jb tidal prediction system and the EGM 2008 geoid,respectively.The data of the tide gauges were defi ned using the GPS buoy and GPS reference stations during the campaigns.The results show that the waveform of the altimeters was slightly contaminated by the small islands.The bias associated with Jason-3 and Sentinel-3A amounted to approximately+20.7±49.7 mm and+30.1±39.4 mm,respectively,which agreed well with the results from other in-situ calibration fi elds.This indicates that the Wanshan area was very suitable as an in-situ calibration/validation fi eld.The wet zenith delay(WZD)determined from the Microwave Radiometer(MWR)and the GPS measurements diff ered from each other for the Jason-3 and Sentinel-3A by−6.6±7.4 mm and 0±6.8 mm,respectively. | Wanlin ZHAI Jianhua ZHU Xiaohui FAN Longhao YAN Chuntao CHEN Zhen TIAN | 2021 | Journal of Oceanology and Limnology2021,39,2: | 1 |
| 5 | Obtaining accurate measurements of the sea surface height from a GPS buoy显示文摘A dedicated GPS buoy is designed for calibration and validation(Cal/Val)of satellite altimeters since 2014.In order to evaluate the accuracy of the sea surface height(SSH)measured by the GPS buoy,twelve campaigns have been done within China sea area between 2014 and 2021.In six of these campaigns,two static Global Navigation Satellite System stations were installed at distances of<1 km and 19 km from the buoy to assess how the baseline length influenced the derived SSH from the buoy solutions.The GPS buoy data was processed using the GAMIT/GLOBK software+TRACK module and CSRS-PPP tool to achieve the SSH.The SSH was compared with conventionally tide gauge(TG)data to evaluate the accuracy of the buoy with the standard deviation of the height element.The results showed that the difference in the standard deviation of the SSH from the buoy and the TG was less than 16 mm.The SSHs processed with different ephemeris(Ultra-Rapid,Rapid,Final)were not significantly different.When the baseline length was 19 km,the SSH solution of the GPS buoy performed well,with standard bias of less than 26 mm between the heights measured by the buoy and TG,meaning that the buoy could be used for Cal/Val of altimeters.The bias between the Canadian Spatial Reference System-precise point positioning tool and the TRACK varied a lot,and some of them were over 130 mm.This deemed too high to be useful for Cal/Val of satellite altimeters.Moreover,the GPS buoy solutions processed by GAMIT/GLOBK software+TRACK module were used for in-orbit Cal/Val of HY-2B/C satellites in ten campaigns.The SSH and significant wave height of the altimeters showed good agreements with the GPS buoy solutions. | Wanlin Zhai Jianhua Zhu Chuntao Chen Wu Zhou Longhao Yan Yufei Zhang Xiaoqi Huang Kai Guo | 2023 | Acta Oceanologica Sinica2023,42,6: | 0 |
| 6 | Measurement of the sea surface using a GPS towing-body in Wanshan area显示文摘Wanshan area has been chosen to be the specified field to calibrate and validate(Cal/Val)the HY-2 altimeter and its follow-on satellites.In March 2018,an experiment has been conducted to determine the sea surface height(SSH)under the HY-2 A ground track(Pass No.203).A GPS towing-body(GPS-TB)was designed to measure the SSH covering an area of about 6 km×28 km wide centered on the HY-2 A altimeter satellite ground track.Three GPS reference stations,one tide gauge and a GPS buoy were placed in the research area,in order to process and resolve the kinematic solution and check the precision of the GPS-TB respectively.All the GPS data were calculated by the GAMIT/GLOBK software and TRACK module.The sea surface was determined by the GPS-TB solution and the tide gauge placed on Zhiwan Island.Then the sea surface of this area was interpolated by Arc GIS10.2 with ordinary Kriging method.The results showed that the precision of the GPS-TB is about 1.10 cm compared with the tide gauge placed nearby,which has an equivalent precision with the GPS buoy.The interpolated sea surface has a bias of–1.5–4.0 cm with standard deviation of 0.2–2.4 cm compared with the checking line.The gradient of the measured sea surface is about 1.62 cm/km along the HY-2 orbit which shows a good agreement compared with the CLS11 mean sea surface(MSS).In the Cal/Val of satellites,the sea surface between the tide gauge/GPS buoy and the footprint of altimeter can be improved by this work. | Wanlin Zhai Jianhua Zhu Chaofei Ma Xiaohui Fan Longhao Yan He Wang Chuntao Chen | 2020 | Acta Oceanologica Sinica2020,39,5: | 0 |