SLR Contribution to Investigation of Polar Motion

SLR technique has being used for determination of ERP during over twenty years. Most of results contributed to IERS are based on analysis of observations of Lageos 1&2 satellites collected at the global tracking network of about 40 stations. Now 5 analysis centers submit operative (with 2-15 days delay) solutions and about 10 analysis centers yearly contribute final (up to 23 years) ERP series. Some statistics related to SLR observations and analysis is presented and analyzed. Possible problems in SLR observations and analysis and ways of its solution are discussed.

💡 Research Summary

The paper provides a comprehensive review of Satellite Laser Ranging (SLR) contributions to Earth Rotation Parameters (ERP), focusing on polar motion (PM) and length‑of‑day (LOD) over more than two decades since the launch of the LAGEOS satellites in 1976. Early SLR measurements, limited by range‑meter precision of several centimeters, have progressed through the introduction of second‑generation laser systems in the early 1980s and third‑generation equipment in the 1990s, achieving sub‑millimeter range accuracy. This technical evolution reduced the root‑mean‑square (RMS) of ERP series dramatically, now delivering Xp, Yp, and LOD with typical uncertainties of 0.1–0.2 arcseconds.

Globally, about 40 stations contribute LAGEOS‑1 and LAGEOS‑2 observations. Five analysis centers currently provide near‑real‑time solutions with a latency of 2–15 days, while roughly ten centers maintain final series spanning up to 23 years. The paper lists the longest continuous series (Table 1) and compares the precision of SLR with GPS, VLBI, and other techniques (Table 2). Notably, the CSR (USA) and IAA (Russia) SLR solutions achieve precision comparable to GPS (≈0.11″) and surpass VLBI in some aspects.

Despite these achievements, the authors identify several persistent challenges. The station network is heavily weighted toward high‑latitude sites in the Northern Hemisphere, leaving Southern Hemisphere and low‑latitude coverage sparse. Reliance on only the two LAGEOS satellites limits geometric diversity and temporal sampling. Observation schedules are vulnerable to weather and equipment downtime, creating data gaps. Moreover, disparate processing strategies and error models across analysis centers hinder uniformity of results.

To address these issues, the authors propose: (1) expanding and upgrading stations in under‑served regions to balance the global network; (2) incorporating additional laser‑retroreflector satellites such as LARES and Starlette to improve orbital geometry; (3) automating observation scheduling and establishing real‑time data transmission to reduce gaps; and (4) adopting standardized analysis software and common error modeling to enhance consistency.

The paper concludes that SLR already provides precision on par with VLBI and GPS for polar motion monitoring, and that implementing the suggested improvements will solidify its role as a cornerstone technique for continuous, high‑accuracy Earth rotation monitoring.