# Contribution of Etalon Observation to Earth Rotation Parameters under a New Observation Scenario
## 2 Data and Methods  
### Data  
SLR observations of the LAGEOS-1/2 and Etalon-1/2 satellites were provided by the ILRS data center in the normal point (NP) form in accordance with the consolidated data format. Original SLR observations from the EUROLAS Data Center (EDC) and Crustal Dynamics Data Information System (CDDIS), which are two data centers of ILRS, were combined for data processing. SLR observations in the interval from 15 February to 15 May of 2019 were processed. For comparison purposes, SLR observations from the same period in 2018 were also analyzed.  
Figure 1 shows the distribution map of SLR stations observing the Etalon-1/2 satellites in the two periods. In total, there were 32 SLR stations involved in the observation of the Etalon-1/2 satellites, of which 30 and 28 stations could observe the Etalon-1/2 satellites in the periods in 2018 and 2019, respectively. Four stations, Svetloe, Russia (1888); Zelenchukskya, Russia (1889); Katzively, Ukraine (1893); and Borowiec, Poland (7811) could observe the Etalon-1/2 satellites only in 2018, and the numbers of NPs of these stations were 7, 11, 8 and 15, respectively. Brasilia, Brazil (7407), and Grasse, France (7845), could provide observations of Etalon-1/2 satellites only in 2019, and the numbers of NPs of these stations were 19 and 594, respectively. In addition, there were only 6 stations distributed in the southern hemisphere, but 26 stations located in the northern hemisphere, most of which were focused in Europe and Asia. The station information, including Site ID, DOMES, Location, Country and Station Coordinates in ITRF2014, is given in Table 1.  
Figure 2 displays the number of weekly SLR observations (NPs) in the two periods. Generally, the number of NPs to the Etalon-1/2 satellites in 2019 was approximately 2 times larger than that in 2018, except for 4 weeks, where the number of NPs in 2018 was almost equal to or larger than that in 2019. On average, there were 202 and 222 NPs for the Etalon-1 and Etalon-2 satellites, respectively, for 7-day solutions in 2019. In contrast, the numbers in the noncampaign period were 140 and 129, respectively. The numbers of NPs for Etalon-1 and Etalon-2 in 2019 were approximately 1.4 and 1.7 times larger than those in 2018, respectively. Figure 3 shows the quantity of NPs in each week for 12 SLR stations, which are sorted by the overall quantity of observations of Etalon satellites. The top 12 SLR stations were Yarragadee (7090), (Wettzell) 8834, (Zimmerland) 7810, (Grasse) 7845, (Matera) 7941, (Hertsmonceux) 7840, (Wettzell) 7827, (Graz) 7839, (Changchun) 7237,  
(Kunming) 7819, (Altay) 1879 and (Komsomsolsk) 1868. Of the 12 stations, the top 4 stations provided 72, 54, 47 and 42 NPs for the Etalon-1/2 satellites on average. In addition, Figure 4 illustrates the number of SLR observations of LAGEOS-1/2 satellites for the 7-day solutions in the periods of 2018 and 2019. On average, the weekly numbers of SLR data points for the LAGEOS-1/2 satellites in 2018 were 1622 and 1285, respectively. The numbers in 2019 were 1433 and 1351, respectively. Compared with that in the period in 2018, the number of NPs for LAGEOS-1 was reduced by 5%, and the number of NPs for LAGEOS-2 was increased by 11%. The characteristic observation minimum occurred in week 4.