Earth Planets Space, Vol. 52 (No. 10), pp. 681-684, 2000LETTER
A. Flores, A. Escudero, M. J. Sedó, and A. Rius
Institut d'Estudis Espacials de Catalunya, Edif. Nexus-204, Gran Capità 2-4, 08034 Barcelona, Spain
(Received December 27, 1999; Revised June 30, 2000; Accepted July 10, 2000)
Abstract: The availability of real-time tropospheric data is an important question for atmospheric parameters to be ingested in weather prediction models or in monitoring studies. In the frame of the EU funded project CLIMAP we have developed an on-line system that acquires GPS data from a number of IGS stations distributed around Europe providing hourly batches of GPS observables. An off-line system processing data with a one-day delay was run during one year to tune the characterisitics of the present on-line system. The hourly data are processed using GIPSY/OASIS II software, to obtain the Zenith Total Delay in a near-real-time basis. Every hour, the new batch is merged with the observations of the previous 23 hours to allow the system to process enough data to yield robust results. The question of what prediction for orbits to use has also been addressed, designing the system to always use the best orbits available from the Center for Orbit Determination in Europe, using the quality codes for the prediction of the orbits to remove "bad quality" satellites from the solution. To validate the results, the ZTD time series for each station have been compared against the solutions obtained through a Precise Point Positioning using final precise orbits and clock corrections. The estimation processing has been tuned to account for the particularities of a near-real-time scenario such as the satellite clock correction and the day boundary issue.