Satellite Laser Ranging for Retrieval of the Local Values of the Love h(2) and Shida l(2) Numbers for the Australian ILRS Stations

This paper deals with the analysis of local Love and Shida numbers (parameters h(2) and l(2)) values of the Australian Yarragadee and Mount Stromlo satellite laser ranging (SLR) stations. The research was conducted based on data from the Medium Earth Orbit (MEO) satellites, LAGEOS-1 and LAGEOS-2, and Low Earth Orbit (LEO) satellites, STELLA and STARLETTE. Data from a 60-month time interval, from 01.01.2014 to 01.01.2019, was used. In the first research stage, the Love and Shida numbers values were determined separately from observations of each satellite; the obtained values of h(2), l(2) exhibit a high degree of compliance, and the differences do not exceed formal error values. At this stage, we found that it was not possible to determine l(2) from the data of STELLA and STARLETTE. In the second research stage, we combined the satellite observations of MEO (LAGEOS-1+LAGEOS-2) and LEO (STELLA+STARLETTE) and redefined the h(2), l(2) parameters. The final values were adopted, and further analyses were made based on the values obtained from the combined observations. For the Yarragadee station, local h(2) = 0.5756 ± 0.0005 and l(2) = 0.0751 ± 0.0002 values were obtained from LAGEOS-1 + LAGEOS-2 and h(2) = 0.5742 ± 0.0015 were obtained from STELLA+STARLETTE data. For the Mount Stromlo station, we obtained the local h(2) = 0.5601 ± 0.0006 and l(2) = 0.0637 ± 0.0003 values from LAGEOS-1+LAGEOS-2 and h(2) = 0.5618 ± 0.0017 from STELLA + STARLETTE. We found discrepancies between the local parameters determined for the Yarragadee and Mount Stromlo stations and the commonly used values of the h(2), l(2) parameters averaged for the whole Earth (so-called global nominal parameters). The sequential equalization method was used for the analysis, which allowed to determine the minimum time interval necessary to obtain stable h(2), l(2) values. It turned out to be about 50 months. Additionally, we investigated the impact of the use of local values of the Love/Shida numbers on the determination of the Yarragadee and Mount Stromlo station coordinates. We proposed to determine the stations (X, Y, Z) coordinates in International Terrestrial Reference Frame 2014 (ITRF2014) in two computational versions: using global nominal h(2), l(2) values and local h(2), l(2) values calculated during this research. We found that the use of the local values of the h(2), l(2) parameters in the process of determining the stations coordinates influences the result.