# _remote sensing_
## 4 Calibration Results
### Jason-3  
Jason-3, which was launched on 17 January 2016, is the successor to the Jason-2, Jason-1, and T/P missions. These series of satellites measured SSH, WS, and SWH since 1992. The mission of these satellites is to provide high quality and global view measurements for ocean science and operational products related to climate change studies, sea level rise, ocean circulation, etc. Jason-3 is an international cooperative satellite altimeter mission between the NASA, National Oceanic and Atmospheric Administration (NOAA), EUMETSAT, and CNES. The ascending Pass No. 153 (before April 2022) and descending Pass No. 012 (after April 2022) flies over the WSCS, which makes it possible to assess the performance of the altimeter. In the Cal/Val of GDR data of Jason-3 altimeter, the CLS 2015 MSS model and HAMTIDE12 tide model were used to maintain the MSS and tidal corrections.  
In WSCS, the strike of Dan'gan-Zhi'wan-Miao'wan islands formed an island chain. The southeast direction of the island chain is the open ocean. Before April 2022, the orbit of Jason-3 follows in the footsteps of the TOPEX/POSEIDON, Jason-1, and Jason-2 missions (Figure 11a). The Pass No. 153 of Jason-3 orbit crosses some small islands of the strike and to Wai'ling'ding island (Figure 11c). The bias has been estimated in the area less than 25 km from the ATGs. There are three points for 1 Hz of data of the Jason-3 altimeter in such an  
Figure 10: The SSH and the calibration results of HY-2C when it flies over the Dan’gan island. Image (**a**) represents the SSH results of the altimeter when it flies over WSCS. The dark green lines represent the Zhi’wan island. The x dots represent the HY-2B SSH of 20 Hz data, and the circles represent the 1 Hz data. Images (**b,c**) were the calibration results for Pass No. 185 and Pass 170, respectively. The red dotted lines in image (**b,c**) represent the drifts of the SSH.  
area and the SSH performed well in the middle point, which is less contaminated by the island and will be used in the Cal/Val. The altimeter has been calibrated using the ATGs of Zhi'wan and Wai'ling'ding islands, and the bias was determined to be \(-4.1\pm 78.7\) mm (Figure 11d).  
After April 2022 (Cycle 301), the Jason-3 changed its orbit and the Pass No. 012 crossed over the WSCS on Er'zhou island, which is about 1 km northeast of Zhi'wan island (Figure 2). The ATGs of Zhi'wan and Dan'gan islands were used to calibrate the SSH south of the islands, south of which was the open sea area, where the land contamination was small. The ATG of Wai'ling'ding island was also used to calibrate the SSH of about 10\(\sim\)20 km from its  
Figure 11: The SSH of Jason-3 when it flies over the WSCS. Images **(a,b)** are examples of the SSH before and after cycle 301 (April 2022). The red x and green dots in images **(a,b)** represent the 20 Hz and 1 Hz SSH data, respectively. The light green areas represent the small islands of the strike to Wai’ling’ding island and Zhi’wan island, respectively, which may contaminate the SSH. Image **(c)** shows the orbits of the two passes. There are about 6 small islands in the red circle that may contaminate the SSH or wet zenith delay of the altimeter. Image **(d)** shows the bias and drift (red line) of the altimeter and the light blue area represents the cycles before 301 (Pass No. 153). The red dotted line in image **(d)** represents the drift of the SSH.  
location (Figure 11b). All the ATGs of the three islands were used for the calibration. The bias of the Pass No. 012 was \(-\)25.8 mm, with a standard bias of 85.5 mm (Figure 11d).  
During 2019 to 2023, there appears to be no obvious drift in the WSCS (about \(-\)0.1 mm/year). Although data were from different passes, the performance of the altimeter in the WSCS is displayed.