The impact of ultra-rapid orbits on precipitable water vapor estimation using a ground GPS network

Since February 2000, the IGS combined ultra-rapid orbits have been available, requested especially for the support of GPS near real-time (NRT) atmospheric monitoring. We have prepared and tested an hourly GPS orbit determination procedure at the Geodetic Observatory Pecný analysis center (GOP AC). The hourly orbits would preferably be used in our NRT tropospheric monitoring, which has been routinely performed since the beginning of 1999, thus far based on 2-day predicted orbits. The advantage of using the sub-daily orbits can be summarized in three contributions: the higher accuracy of the results (about 10–20 %), the stability of the evaluation (fewer weak periods, excluded results, etc.) and the significant simplicity of the procedure (e.g. orbit selection, orbit fixing).