The Global Differential GPS (GDGPS) system developed by JPL aims at seamless global real-time positioning at the dm accuracy level for dual-frequency receivers either fixed or mobile, anywhere and at any time. The GDGPS system relies on GPS data transmitted in real-time to a central processing center at JPL from a global network of permanently operating GPS dual-frequency receivers. At the processing center, the Internet-based Global Differential GPS (IGDG) system, the heart of JPL’s GDGPS, generates and disseminates over the open Internet special 1-s global differential corrections (IGDG corrections) to the GPS broadcast ephemerides. The IGDG corrections enhance the accuracy of GPS broadcast orbits and clocks down to the dm level and serve as the key-factor for high-precise real-time positioning of a stand-alone receiver. An experimental verification of the dm positional accuracy of the IGDG system was carried out in the Netherlands, by means of both a static and a kinematic test. During the static test GPS data were collected for 5 consecutive days using a fixed immobile receiver and processed as if in real-time. Within the framework of the kinematic test, an experiment was carried out using a kinematic platform. Our tests confirmed the dm accuracy of stand-alone receiver positioning with IGDG. The standard deviation for positioning both in static and kinematic mode appears to be 10 cm in each horizontal component and 20 cm in the vertical component. More than 99% of the IGDG corrections were received with the expected 1-s interval in the field via mobile communication, the latency of the corrections was generally from 7 to 8 s.@en

Increased knowledge of atmospheric water vapor can improve weather predictions and is expected to reduce errors in products derived from GPS and (In)SAR data. At GPS ground stations Integrated Water Vapor (IWV) is estimated from the GPS signal delay with a high temporal resolution. The Envisat MERIS spectrometer obtains spatially dense IWV observations but at limited moments in time. In this research the additional value of MERIS IWV is evaluated when added to GPS IWV for the purpose of obtaining a high quality spatial-temporal water vapor product. At each of 39 stations, first GPS IWV from surrounding stations is used to produce a two months time series of IWV with a temporal resolution of one hour. Then both GPS and MERIS IWV are used together. The two resulting time series are validated against direct GPS IWV as measured at the station.@en