Estimation of the Length of Day (LOD) from DORIS observations

We estimated the true Length of Day (LOD) from DORIS observations. The DORIS RINEX data has been processed by the DORIS development version of the Bernese GPS Software 5.2. We performed single satellite and multisatellite (Sentinel-6A, Sentinel-3A, Sentinel-3B, Jason-3, HY-2C, HY-2D, SARAL, and Cryosat-2), and pre-eliminated solutions. The DORIS data has been processed separately for each satellite on the basis of daily arcs. The troposphere, frequency offset, and orbit parameters were pre-eliminated from the normal equation systems and the finalized matrices were combined on a weekly basis. Hence, individual satellite solutions as well as multi-satellite combined solutions were created. From this solution, we calculated the transformation parameters w.r.t. ITRF 2020 (more precisely w.r.t. the DORIS extension DPOD 2020,) and after applying the 7-parameter Helmert transformation we calculated the RMS w.r.t. DPOD 2020.

We performed solutions with different settings, in particular with different handling of cross-track once-per-revolution harmonic parameters (adjusted with different constraints or not adjusted), since the amplitude of the sine term correlates with LOD. For a comparison of our results, we used the IERS 20 C04 model as a reference.