# Contribution of Etalon Observation to Earth Rotation Parameters under a New Observation Scenario
## 3 Results  
### Station Coordinates  
The differences in the repeatability of station coordinates between the LAGEOS-only solutions and LAGEOS+Etalon solutions in 2019 are displayed in Figure 5. A better repeatability for the LAGEOS-only solutions is presented by positive values, while the opposite result is illustrated by negative values. The SLR stations are sorted according to the number of 7-day solutions. Of the 23 stations listed in Figure 5, 10, 13 and 10 stations show negative values in the N, E, and U components, respectively. Generally, the differences in coordinate repeatability in all three components are within the range of \(-\)1 mm and 1 mm. However, there are few exceptions, e.g., Potsdam (7841), Wettzell (8834), Altay (1879), and Beijing (7249), for which the repeatability of at least one component of the coordinates is approximately 3 mm. For the Potsdam (7841) and Wettzell (8834) stations, the differences in coordinate repeatability in the N, E, and U components are approximately 1.5 mm, 2 mm, and 3 mm, respectively, which may be caused by the nosier Etalon observations, especially for station Wettzell (8834), which is a high-performing site contributing to the observations \begin{table}
\begin{tabular}{c c} \hline \hline
**Table 2008** & **Description** \\ \hline Geopotential & EGM2008 model (degree and order 30) \\ Third-body & DE405: Sun, Moon, Jupiter, Venus, Mars; \\  & Ocean tides: CSR 4.0A \\ Tide forces & Solid Earth tides: IERS conventions 2010 \\  & Atmospheric tides: Ray and Ponte model 2003 \\  & Direct radiation: applied \\ Solar radiation pressure & CR: 1.13 for LAGEOS-1/2 \\  & CR: 1.20 for Etalon-1/2 \\ Albedo radiation & Not applied \\ Earth thermal radiation & Applied \\ Relativistic correction & IERS Conventions 2010 \\ Numerical integration & Adams collocation method; 12 th order, \\  & step size: 120 s \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Force models of LAGEOS+Etalon solutions. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Description** \\ \hline \hline  & One set per week arc \\ Orbit parameters & 6 Keplerian orbit elements (7 days) and 5 empirical parameters, \\  & S0, SS, SC, WS, WC \\  & One set per week arc \\  & Core stations: Network constrains \\ Station coordinates & Minimum constraint: no net rotation \\  & and no net translation \\  & Noncore stations: freely estimated \\ Range biases & One set per week arc, estimated only for selected stations \\  & recommended by ILRS \\ ERPs & Xp, Yp, LOD (1-day), piecewise constant \\ Geocenter coordinates & Three parameters in \(x\), \(y\), \(z\) components, piecewise constant \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Characteristics of parameters estimated in LAGEOS+Etalon solutions. of Etalon-1/2 satellites. For stations Altay (1879) and Beijing (7249), the differences in the repeatability of station coordinates between LAGEOS-only solutions and LAGEOS+Etalon solutions are \(-\)3.22 mm, \(-\)1.55 mm, and \(-\)0.59 mm, respectively, which may be related to the improved observation geometry. In addition, the impact of the increased quantity of observations of Etalon satellites on the station coordinates in the 2019 campaign is analyzed for four stations in detail, stations Yarragaede (7090), Wettzell (8834), Komsomolsk (1868), and Altay (1879). Figures 6-9 present the residuals of the weekly Helmert transformation with respect to SLRF2014 for the LAGEOS-only solutions and LAGEOS+Etalon solutions of 2019 for those four stations. For most of the top 12 stations contributing to the observations of Etalon satellites, such as Yarragaede (7090) and Wettzell (8834), the ratio of the number of observations between Etalon and LAGEOS lies within 10% and 35%. From Figures 6 and 7, we can observe similar values for the residuals of the N, E, and U components of the Helmert transformation for LAGEOS-only solutions and LAGEOS+Etalon solutions.