# Analysis of Precise Orbit Determination for the HY2D Satellite Using Onboard GPS/BDS Observations
## 5 Conclusions  
Based on the spaceborne BDS and GPS data of the newly launched HY2D satellite, this paper conducts research into POD using one month of data. The model strategies are developed to solve the precise orbits of the HY2D satellite, and this study selects a month of real onboard GPS and BDS data to validate the developed model strategies. The main conclusions of the study are given in the following:  
1. The standard deviation of the POD residuals based on spaceborne BDS and GPS data are, respectively, 9.12 mm and 8.53 mm, and these residual variations show no significant deviations or systematic errors.
2. The comparison results with DORIS-derived orbits show that the average radial RMS value of spaceborne BDS and GPS are 1.5 cm and 1.4 cm, respectively, and the corresponding 3D RMS accuracy are 5.3 cm and 4.3 cm, respectively. Overall, these results indicate that the POD processing of the HY2D satellite using spaceborne BDS and GPS data can achieve 1 cm radial precision and satisfy the current high-precision altimetry applications.
3. According to the SLR validation results, it is shown that the standard deviation of residuals is 3.3 cm, which indicates that the orbital accuracy of the HY2D satellite is approximately 3.3 cm, and the used model strategy is also reliable.  
As an example of the HY2D satellite, this study adopts spaceborne BDS and GPS data to conduct POD research. Eventually, the model strategies are developed to solve the precise orbit of the HY2D satellite. Meanwhile, we use the external DORIS-derived precise  
Figure 10: The variation of SLR residuals for HY2D satellite.  
orbit of the HY2D satellite and SLR normal point data to validate the calculated orbit, and the results show that the HY2D satellite can achieve 1 cm radial precision.  
[PERSON] provided the initial idea for this research; [PERSON], [PERSON], [PERSON] and [PERSON] collected the experimental data and conducted the experiment; [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] analyzed the results of the experiment; [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] wrote the paper. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the National Key Research Program of China \"Collaborative Precision Positioning Project\" (No. 2016 YFB0501900), the National Natural Science Foundation of China (Grant No. 42174222, 41904165, 62101219, 41804019), the State Key Laboratory of Geodesy and Earth's Dynamics self-deployment project (No. S21L6101, S21L8101), the Natural Science Foundation of Hubei Province (No. 2017 CFB372), the Natural Science Foundation of Jiangsu Province (No. BK20210921), the Natural Science Foundation of Fujian Province (No. 2018J01480).  
Not applicable.  
The authors acknowledge the satellite information of HY2D provide by NSOAS. Our sincere thanks to the NSOAS for providing space-borne GPS and BDS data for HY2D; CODE for providing GPS satellite orbits, clocks and Earth rotation parameters; the CNES for providing precise orbits for HY2D; the ILRS for providing SLR data of the HY2D satellite. Meanwhile, we would like to thank the anonymous reviewers for their valuable comments.  
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.