Limits on Tropospheric Corrections From Natural Variations

James R. Clynch

Abstract:	The limitations of the accuracy of tropospheric corrections were studied using data taken from upper air weather soundings. Ten to fourteen days of data with twice daily launches from 6 coastal sites were used. These were widely distributed throughout the world. A ray trace program was used to determine the delay and bending at elevation angles from 0 to 90 degrees. The mean and standard deviation of the delay at each site were computed. In addition the average obliquity factor, the ratio of the delay to the zenith delay, was found for each site. The absolute delay varied significantly over the sites - ranging from 10 to 13.5 m at 10 degrees for example. The obliquity factor had considerably less variation. This shows the utility of having real surface weather data. However, it is felt that the variation in the obliquity may represent the ultimate limit on tropospheric corrections. Data from the three California stations, at Oakland, Vandenburg, and San Diego, were used to study the utility of using data from a distant site to make corrections. It was found that the absolute range delay error could be reduced by 90 percent using data from 300 to 600 km away. This is essentially equivalent to using a water vapor radiometer at a distant site. This applies only if the stations are in the same air mass.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	2278 - 2284
Cite this article:	Clynch, James R., "Limits on Tropospheric Corrections From Natural Variations," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 2278-2284.
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