Estimation of the Length of Day (LOD) from recent DORIS Observations

This study investigates the estimation of the Length of Day (LOD) using DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) RINEX data from 2015 to 2023, comparing results with  the IERS 20 C04 model. Observations from 10 satellites were analyzed using DORIS-specific modification of the Bernese GNSS software, with varying durations of data availability across the nine years. The analysis explores the variability in Earth's rotation, attributing changes to dynamic factors influencing angular momentum. Various solution versions  with different parameter constraints were evaluated. Statistical analysis reveals that the low constrained cross track once per revolution parameters provided less  reliable results.

Key findings reveal a close alignment between DORIS-derived LOD values and the IERS 20 C04 model, for satellite combinations, with a weighted mean of 7 µs and a weighted standard deviation of 87 µs . Single-satellite analyses highlight the contributions of specific satellites, such as Cryosat, Saral, and Sentinel-6, in capturing unique geophysical processes. Improved data precision and modeling were observed over the years, reflecting advancements in satellite instrumentation and operational protocols. Statistical analysis emphasizes combining multiple satellite datasets for more reliable LOD estimates, as single-satellite solutions showed higher variability and biases.

Spectral analysis identifies dominant periodic signals, such as annual and semi-annual cycles, and variations induced by tidal and orbital mismodeling. The impact of relativistic effects was evaluated, demonstrating the significant role of Lense-Thirring corrections in precise LOD modeling. A comparison of different subdaily  motion models revealed subtle differences in periodic signal amplitudes. This work underscores the possibility of precise LOD estimation from DORIS data, on condition of high-quality satellite data and refined modeling techniques for accurate Earth rotation studies, providing insights into temporal variability in LOD and contributing to geodetic and geophysical research.