GPS meteorology: validation and comparisons with ground-based microwave radiometer and mesoscale model for the Italian GPS permanent stations

Ground-based GPS meteorology has been developed during the last decade. Beside the GPS traditional application for precise geodesy, the GPS system has proved to be a powerful tool in atmospheric studies, such as climatology and meteorology. During 1999, at the Space Geodesy Center (CGS) of the Italian Space Agency (ASI) an operative and automatic system was developed in order to produce GPS tropospheric parameters on a daily basic for the Italian GPS permanent stations. In this work the operational processing of the GPS data is described. Moreover, the validation of the GPS tropospheric parameters through a comparison with other independent GPS solutions as well as independent techniques is presented. The GPS internal validation of zenith tropospheric delay (ZTD) shows a bias of 5 mm (absolute values) and a standard deviation ranging from 4 to 20 mm. For a few stations a comparison is performed between the GPS derived precipitable water vapor (PWV) and both the one computed using the MM5 and the one measured by the water vapor radiometer (WVR) and radiosondes (RAOB). The agreement between GPS and MM5 is within the range of 2–7 mm; for GPS, WVR and RAOB the standard deviation ranges from 0.85 to 1.62 mm.