# Contribution of Etalon Observation to Earth Rotation Parameters under a New Observation Scenario
## 5 Conclusions  
Under the coordination and endeavors of ILRS, the number of SLR observations of Etalon satellites in the 3-month campaign period of 2019 increased significantly. On average, the numbers of weekly observations of Etalon satellites in 2019 were 202 and 222, which were 1.4 and 1.7 times larger than those in 2018. The ratio between SLR observations of Etalon satellites and those of LAGEOS satellites increased from 9.2% to 15.2%. For some specific SLR tracking stations, such as Komsomolsk (1868) and station Altay (1879), the ratio between the number of observations of Etalon satellites and that of LAGEOS satellites was approximately 50%. Based on the data from this new observation scenario, the effect of increased Etalon observations on most geodetic parameters generated by ILRS was investigated in this paper. Based on the analysis of the repeatability of station coordinate estimation, the impact of the increased Etalon observations of the new tracking scenario in 2019 on station coordinates was marginal. For most of the SLR stations, the differences in repeatability for station coordinates of LAGEOS-only solutions with respect to those from LAGEOS+Etalon solutions were between \(-\)1 mm and 1 mm. For some high-performance stations, the maximum value of differences in all components was approximately 3 mm, which was lower than the impact of LEO satellites on station coordinates. However, for SLR stations not dedicated to LAGEOS satellite tracking, the RMS values of residuals in the N, E, and U components were reduced by 3.1 cm, 2.0 cm and 2.3 cm, respectively. Under the new observation scenario, the LAGEOS satellites' orbit was affected by less than 1 cm. However, the internal precision of Etalon-1/2 satellites in T and N directions was improved by 1.5 cm and 2.9 cm, respectively. The most significant improvement gained by processing more Etalon observations from the campaign period could be seen in the recovery of theERPs. Compared with IERS-14-C04 series, the standard deviation of Xp was reduced from 179.97 \(\upmu\)as to 167.64 \(\upmu\)as; that of Yb was reduced from 270.45 \(\upmu\)as to 231.90 \(\upmu\)as; and that of LOD was improved from 47.58 \(\upmu\)s/day to 45.13 \(\upmu\)s/day. The standard deviations of Xp, Yb and LOD could be improved by 6.9%, 14.3% and 5.1%, respectively. The comparison with IERS-14-C04 series demonstrates that using the more Etalon observations under the new observation scenario improves the consistency between ERPs estimated with SLR and that from other space geodetic techniques. So, it can be concluded that the more Etalon observations under the new observation scenario are more beneficial for the estimation of ERPs, especially polar motion. The results presented in this paper serve as an example of the possible advantages of increasing the observations of Etalon satellites. In this study, the impact of Etalon observations on the ILRS product was evaluated with only a 3-month tracking campaign, and a longer period analysis covering one year or more would allow a more precise conclusion on the impact of SLR observations to Etalon satellites on more geodetic parameters, such as geocenter coordinates and scale. Thus, with our improving ability to track high-orbiting satellites, such as GNSS satellites, the ILRS should increase efforts on tracking Etalon satellites, including increasing the number of passes and data volume for Etalon satellites in the future. Conceptualization, X.Z. and Y.K. ; methodology, X.Z. ; software, X.Z. and Y.K. ; validation, X.Z., and Y.K. ; formal analysis, X.Z., Y.K. and D.Z. ; investigation, X.Z. ; resources, X.Z., Y.K. and D.Z. ; data curation, X.Z. ; writing--original draft preparation, X.Z. ; writing--review and editing, Y.K. and X.L. ; visualization, X.Z. ; supervision, D.Z. and X.L. ; project administration, D.Z. and X.Z. ; funding acquisition, X.L. All authors have read and agreed to the published version of the manuscript. This research was funded by the Natural Science Foundation of Shaanxi Province, China (grant number: 2021 JQ-656).