Analysis of the Utility of NOAA-Generated Tropospheric Refraction Corrections for the Next Generation Nationwide DGPS Service

Sunil B. Bisnath, David Dodd and Allen Cleveland and Michael Parsons

Abstract:	The U.S. Coast Guard has begun the modernization of its Nationwide Differential GPS (NDGPS) beacon network. One potential component of modernization is the transmission of not only pseudorange corrections but also pseudorange and carrier phase measurements from reference stations. Such an augmentation could provide for long baseline, centimeter-level, differential carrier phase processing. In order to achieve precise, long baseline results, improved handling of atmospheric refraction of the incoming GPS signals must be achieved. Assuming ionospheric- free data processing, the modeling of tropospheric delay becomes the limiting factor. The Forecast Systems Laboratory at the National Oceanic and Atmospheric Administration (NOAA) has developed an experimental tropospheric delay product within the continental U.S. (CONUS). The purpose of this paper is to analyze the accuracy of the NOAA tropospheric product and quantify its usefulness in GPS data processing. The accuracy of the NOAA tropospheric delays was determined by comparison against GPS estimated delays from the International GPS Service (IGS) and from existing tropospheric delay models. The NOAA zenith total tropospheric delay r.m.s. difference ranged from 15 to 25 mm. The WAAS model comparison r.m.s. values were larger and the Saastamoinen and Hopfield models even larger. As expected, these latter three models showed significant station-dependent variation. The utility of the NOAA tropospheric delays in position determination was accomplished by supplying the NOAA zenith delay estimates to an in-house ionospheric-free relative GPS processor. Results indicate that the most significant improvement is observed in up-component bias reduction of a few centimeters to more than a decimeter. Follow-on work involves processing more varied data sets; refining current GPS data processing; suggesting methods of disseminating the NOAA corrections; and performing a similar analysis with experimental ionospheric products.
Published in:	Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004) September 21 - 24, 2004 Long Beach Convention Center Long Beach, CA
Pages:	1288 - 1297
Cite this article:	Bisnath, Sunil B., Dodd, David, Cleveland, Allen, Parsons, Michael, "Analysis of the Utility of NOAA-Generated Tropospheric Refraction Corrections for the Next Generation Nationwide DGPS Service," Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, September 2004, pp. 1288-1297.
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