## 5 Conclusions  
This paper presents a comparative analysis of SLR observations with regard to BDS satellite precise orbit products generated by CODE, GFZ, WU, and ESA as part of the IGS MGEX campaign. The analysis covers the period from February 2017 to March 2021. The monthly number of SLR observations for MEO and IGSO satellites is around 250 and 150, respectively. CSPAD and MCP stations provide most of the observations, with roughly equal numbers for MCP observations and CSPAD observations of MEO satellites. For BDS-2 IGSO satellites, CSPAD observations outnumber MCP observations by a factor of two. However, there are only a few observations from PMT stations, which limits their ability to evaluate accuracy. This study primarily focuses on comparing the signature effects of CSPAD and MCP detectors. The SLR residuals of IGSO satellites exhibit a greater dependence on nadir angle compared to MEO satellites, which can be attributed to the presence of more corner cubes on LRAs. The RMS of the SLR residuals of MCP stations is about 40 to 56 mm, which is about 5 mm smaller than that of CSPAD stations. As a representative of high-energy stations, Yarragadee provides most of the observations between MCP and PMT stations. The slope with regard to the nadir angle is approximately \(-1.0\) and \(-3.5\) mm/deg for MEO and IGSO satellites, respectively. Compared with Yarragadee, the slope of SLR residuals observed by Shanghai equipped with a single-photon detector is about \(-0.8\) and \(-1.0\) mm/deg, respectively. The correlation between SLR residuals and nadir angle of multi-photon stations is larger than that of single-photon stations, which may prove that the signature effect of multi-photon stations also exists in the SLR observations of BDS. The slope with regard to the nadir angle of BDS-3 CAST for single-photon and multi-photon stations is about 0.8 and 0.1 mm/deg, respectively, which may be caused by the material of the prism cubes or other components on LRAs. Considering the number and the quality consisting of signature effects for SLR stations, seven stations--five C-SPAD and two MCP station--can be regarded as high-performing stations. The results show that these stations can reduce the RMS of SLR residuals for all constellations by about 1 to 3 mm. The RMS of the SLR residuals of CODE for the BDS-2 MEO and BDS-2 IGSO satellites is 56 and 65 mm, respectively. For GFZ, WU, and ESA, the resulting RMS of the SLR residuals are 61, 53, 51, and 65 mm; 62, 46, 52, 62 mm; 120, 51, 50, and 36 mm, for BDS-2 IGSO, BDS-2 MEO, BDS-3 CAST, and BDS-3 SECM, respectively. The mean offset of the SLRresiduals varies significantly between ACs. Excluding the results for the BDS-2 satellites from ESA, the difference between the other three ACs is typically around 10 to 15 mm. This discrepancy is attributable to differences in both non-conservative force models and AC strategies for new GNSSs. Upon comparing the mean offset and RMS of each AC, it becomes evident that there are discrepancies. The RMS value above 110 mm suggests that ESA may have a modeling error with BDS-2 IGSO satellites. Additionally, GFZ and WU may have modeling defects with BDS-3 satellites due to the similarity in the slope with regard to elongation between BDS-3 MEO and BDS-2 IGSO. Through strategic analysis of the differences among ACs, it can be inferred that utilizing an appropriate PBW model could enhance the accuracy of SRP modeling and result in more consistent performance. Conceptualization, X.L. and C.L. ; methodology, X.L. and C.L. ; software, C.L. ; validation, C.L. ; formal analysis, C.L. ; investigation, C.L. and Y.Y. ; resources, K.Z. ; data curation, C.L. ; writing--original draft preparation, C.L. ; writing--review and editing, C.L. and Y.Y. ; supervision, C.L. ; project administration, X.L. and Y.Y. ; funding acquisition, X.L. and Y.Y. All authors have read and agreed to the published version of the manuscript. This research was funded by the National Natural Science Foundation of China (Grant No.