Knowledge Bank

In the past Earth Rotation Parameters (ERP), i.e., polar motion and UT1-UTC values, have been determined using data from only one observational system at a time, or by the combination of parameters previously obtained in such determinations. The question arises as to whether a simultaneous solution using data from several sources would provide an improved determination of such parameters. In order to consider the promise of this more fully, 15 days of observations have been simulated using realistic networks of Lunar Laser Ranging (LLR), Satellite Laser Ranging (SLR) to Lageos, and Very Long Baseline Interferometry (VLBI) stations. Then a comparison has been done of the accuracy and precision of the ERP obtained from: a) the individual system solutions, b) the weighted means of those values, c) all of the data, via the combination of the normal equations obtained in a), and d) a grand solution with all the data. These simulations show that solutions done by the normal equation combination and grand solution methods provide the best or nearly the best ERP for all of the periods considered, but that weighted mean solutions provide nearly the same accuracy and precision. VLBI solutions also provide ERP of similar accuracies. The simulations also indicate that ERP recovery at the 1 mas level for polar motion, and the 0.2 to 1.0 ms level for UT1-UTC is at the limit of all current techniques, without increasing the observational accuracies, or the number of stations.