# _remote sensing_
## 6 Conclusions  
From August 2019 to June 2023, the WSCS has been in operation for over three years now and has completed multiple satellite calibrations [3; 15]. Two PGSs of Zhi'wan and Wai'ling'ding islands were processed using the GAMIT/GLOBK and Hector software to analyze the trend of this area, especially in U direction. The datum of the three ATGs in WSCS were measured using the DGB each year, to guarantee the same datum with the altimeters after translation. The sea surface was measured to make connections between HY-2B altimeter footprints and the ATG of Zhi'wan island. Moreover, peripheral data such as the sea level of B319 and the hydrological station data (Dan'gan island) and the adjacent GNSS data were also used for the calibrations. The global MSS and tide models were used to maintain the MSS and tidal corrections between the ATGs and the altimeter footprints. The above data and technology support the Cal/Val of WSCS altimeters in this research. The series of islands on the southwest side of the WSCS have a certain impact on the SSH product of the satellite altimeter. The SSH of the satellite altimeter was good at the sub satellite point about 15 km away from these islands. Among them, S3A satellite altimeter data is the best, and its SAR mode can monitor sea level change information of about 350 m.  
From August 2019 to April 2023, the SSH of HY-2B, HY-2C, Jason-3, and S3A was calibrated using the facilities of WSCS. The mean bias of HY-2B was -16.7 \(\pm\) 45.2 mm, with  
Figure 13: The planning devices (red triangle) and the area of WSCS (blue lines). The planning devices include the moored GNSS buoy, the bottom pressure tide gauge, and the hydro-meteorological buoy, which will be placed at the footprint of HY-2B altimeter. The blue lines represent the area of WSCS, which can be used for the Cal/Val of a wide swath altimeter such as SWOT. a drift of 0.5 mm/year. The HY-2C biases were \(-\)18.9 \(\pm\) 48.0 mm for Pass No. 170 with drifts of 0.0 mm/year and \(-\)5.6 \(\pm\) 49.3 mm for Pass No. 185 with \(-\)0.3 mm/year drifts, respectively. The Jason-3 altimeters changed their orbits on April 2022 and the biases were \(-\)4.1 \(\pm\) 78.7 mm and \(-\)25.8 \(\pm\) 85.5 mm for Pass No. 153 and 012, respectively. The absolute biases of S3A were determined to be \(-\)16.5 \(\pm\) 46.3 mm with a drift of \(-\)0.6 mm/year and \(-\)9.8 \(\pm\) 30.1 mm with a drift of 0.5 mm/year for Pass No. 260 and 309, respectively. The function of the calibration sites for satellite altimeters is to unify different satellite altimeters to the same datum, thereby ensuring the continuity of satellite altimeter measurements. This continuity has been maintained for over 30 years [1; 5; 6]. The construction and professional operation of the WSCS will inject new strength into the calibration of satellite altimeters in the future, providing data for the global Cal/Val of altimeter measurements. In the future, new altimeter calibration points and higher precision regional MSS and tide models will be established to ensure the uniformity in the Cal/Val of multi-source satellite altimeters. Methodology, W.Z. ([PERSON]), J.Z., H.P., C.C., L.Y., H.W., W.Z. ([PERSON]) and H.G. ; Resources, H.P., C.C., H.W., X.H., W.Z. ([PERSON]), H.G. and Y.Z. ; Data curation, W.Z. ([PERSON]), H.P., C.C., L.Y., X.H., W.Z. ([PERSON]), H.G. and Y.Z. ; Writing--original draft, W.Z. ([PERSON]); Writing--review & editing, C.C. and L.Y. ; Funding acquisition, J.Z. All authors have read and agreed to the published version of the manuscript. This research was funded by National Key Research and Development Program of China, grant number 2021 YFC2803304; Hainan Province Science and Technology Special Fund, grant number ATIC-202301003; Shandong Province for Pilot National Laboratory for Marine Science and Technology (Qingdao), grant number LSKJ202201302, 2019B02; National Satellite Ocean Application Service, grant number G623 CY125.