High-precision GNSS orbit, clock and EOP estimation at the United States Naval Observatory

The United States Naval Observatory (USNO) produces GPS-based estimates of satellite orbits, satellite- and receiver-clock time corrections, and earth-orientation parameters five times per day: once in a daily “rapid” process, the results of which are available with approximately 16-hour latency, and four times in an every-six-hours “ultra-rapid” process, the results of which are available with 3-hour latency. The rapid products supply 24 hours of post-processed estimates; the ultra-rapid products supply 24 hours of post-processed estimates with 24 hours of predictions. As is, the ultra-rapid products are suited for real-time systems where high-accuracy GPS orbits are required. In addition to providing high precision and low latency, these products are available on an extremely reliable basis. USNO is one of the few DoD providers of these GPS-based estimates and performs duties as an Analysis Center (AC) of the International GNSS Service (IGS). Recently, the USNO has begun testing on incorporating GLONASS observational data into a non-operational “rapids” processing. The resulting solutions from this case study will be compared to a USNO's GPS-based control solution as well as to the combination rapid products produced by the IGS. It is shown that the network stations used in the GLONASS test case have a noticeable improvement in in their position estimate RMS in comparison to the control solution. Performing a 7-parameter Helmert transformation indicates that the Z-direction rotational values appear to have the most improvement from the inclusion of the GLONASS observations.