# Contribution of Etalon Observation to Earth Rotation Parameters under a New Observation Scenario
## 1 Introduction
The results demonstrated that the SLR data of active Sentinel satellites contributed greatly to the determination of ERPs and geocenter coordinates [25]. [PERSON] et al. investigated the contribution of seven LEO satellites to ERPs estimation. The results show that the combination of LEO observations improves the Xp, Yp and LOD by 0.644 ms, 0.629 ms and 0.028 ms, respectively [26]. In 2021, [PERSON] et al. analyzed the station coordinates estimated by SLR observations of LEO, Laser Relativity Satellite (LARES), LAGEOS and Galileo satellites. The results showed that the consistency in the horizontal components of the coordinates of noncore stations can be increased by 10% [27]. However, the full employment of GNSS satellites and LEO satellites is still hindered by the lack of precise models for perturbation forces, such as air drag for LEO satellites and solar pressure for GNSS satellites, and deficiencies in the measurement models of certain parameters, such as station-specific range biases for LEO and GNSS satellites. Apart from employing observation from satellites with different orbit characteristic, some researchers have analyzed the impact of constructing new sites in the present SLR tracking network on SLR products by simulations. The results demonstrated that it would be useful to add a new station in the southern hemisphere and that the most effective place for the new SLR station differs for different geodetic parameters [28; 29]. However, the addition of new SLR stations is limited by high costs. Compared with GNSS and LEO satellites, Etalon satellites are a good tool for the definition of geocenter coordinates, ERPs and other ITRF parameters, due to their spherical shape, large area-mass ratio and high number of corner cubes. In some previous studies, it was shown that the impact of Etalon observations to SLR processing was limited by its low number of observation, which is approximately 10% of that of LAGEOS [30; 31]. Therefore, [PERSON] et al. investigated the impact of changing the tracking methods of the LAGEOS and Etalon satellites on SLR standard products. With the simulation of different tracking conditions, the results showed that the quality of parameters related to the ITRF does not significantly degrade with a decrease of 20% in the quantity of data from LAGEOS-1/2 and that the ERPs can be improved by 10% when the number of SLR measurements of Etalon satellites under the new conditions is three times more than that of the routine observation scenario [32]. However, with the improvement in the ability of the ILRS network to track high-altitude satellites, the ILRS Analysis Standing Committee (ASC) proposed conducting a 3-month tracking campaign with Etalon satellites from February 15 to May 15 in 2019, during which the number of passes and observations of the two Etalon satellites increased. Thus, it is worthwhile to process the Etalon observations from the campaign and to analyze their impact on the ILRS routine products, including station coordinates, ERPs, satellite orbit and so on. This paper delivers the first investigation of the contribution of more Etalon observations from the new real observation conditions to ILRS products, especially to the ERPs, station coordinates and satellite orbit. The impact of Etalon observations was evaluated by comparing ILRS products estimated from LAGEOS-only solutions and those from LAGEOS+Etalon solutions. SLR data of Etalon and LAGEOS satellites from non-campaign period were also processed for comparison purposes. This paper is organized as follows: In Section 2, we present the SLR data used for the estimation of ITRF-relevant parameters in detail. In Section 3, the approaches employed for the processing of the LAGEOS and Etalon satellite data are illustrated. In Section 4, we describe the results of SLR data processing, in particular, the station coordinates, ERPs and satellite orbit. Finally, in Section 5, a summary of the work is given, and conclusions are drawn.