Reducing satellite orbit error effects in near real-time GPS zenith tropospheric delay estimation for meteorology

We investigate the influence of using IGS predicted orbits for near real-ti me zenith tropospheric delay determination from GPS and implement a new pro cessing strategy that allows the use of predicted orbits with minimal degra dation of the ZTD estimates. Our strategy is based on the estimation of the three Keplerian parameters that represent the main error sources in predic ted orbits (semi-major axis, inclination, and argument of perigee), and the ir associated variance directly from the real-time GPS data set. A comparis on with the use of IGS final orbits shows a negligible bias and an rms less than 6 mm in the ZTD estimates at all the stations. The improvement compar ed to a strategy based only on the quality index provided with the predicte d orbits is 20%. The level of accuracy and turn-around time shown here meet the current requirements for operational meteorology.