Automatic orbit quality control for near real-time GPS zenith troposphericdelay estimation

We implement an automatic orbit quality control procedure in order to reduc e the effect of satellite orbit error for near real-time estimating of zeni th total delay (ZTD). We estimate the three Keplerian parameters of the GPS orbits that represent the main error sources (semimajor axis, inclination, and argument of perigee). We start with an a priori constraint correspondi ng to the typical orbit accuracy for each parameter and adjust it iterative ly according to its estimated value and variance. This data analysis proced ure shows an improvement of 20% in ZTD rms compared to a strategy based onl y on the quality index provided with the IGS predicted orbits. A real-time test with IGS ultra-rapid orbits also shows significant improvement compare d to fixing IGS ultra-rapid orbits. This strategy allows for a totally auto mated estimation of orbital parameters directly from the real-time GPS data , without altering the accuracy of the ZTD estimates. (C) 2001 Elsevier Sci ence Ltd. All rights reserved.