The application of GPS/Glonass technology to atmospheric monitoring

Richard Percival

Abstract:	Quartzlock (UK) Ltd is a small UK company, specialising in the generation, distribution and measurement of stable and accurate time and frequency signals. The GPS disciplined oscillator (GPS-DO) range has been in production since late 1994. Realising that the introduction of selective availability (SA) had introduced serious problems into the use of GPS-DO’s as a precise time and frequency instruments, the company decided to design its own GPS engine. The result was a dedicated time and frequency engine, not a navigation engine pressed into time and frequency use. The engine uses the excellent Carrier Phase Tracking technology, in addition to the normal C/A code tracking used in most normal instrumentation. The possible applications for such a high precision time and frequency standard are large. One area the company has recently entered is GPS meteorology. This is the application of GPS data to the monitoring and analysis of atmospheric conditions. Atmospheric monitoring can be done by both ground-based and space-based GPS applications. Ground based GPS receivers at locations can be used to gather data that can be shown to determine integrated Precipitable Water Vapor (PWV). The measurement of PWV is the backbone of operational weather forecasting, and weather and climate research. Present data systems provide inadequate resolution of the temporal and spatial variability of water vapor, and this is the main stumbling block to improving short-range precipitation forecasts. Recent studies have shown that GPS-determined PWV observations can significantly improve weather forecasting accuracy, both in the short and long term. GPS can be used to establish precise location through the time of flight of L-band signals at different frequencies from multiple satellites to a single receiver. In this case, the parameter of interest to the user is the signal path delays recorded by GPS receivers at fixed locations. These delays will be caused by a variety of effects. One cause of these delays is due to the passage of the signals through the Earth’ ionosphere and atmosphere. The delay of the signal through the ionosphere is frequency dependent, and may be determined by observation of both the L1 (P-code and C/A code) and L2 (P code only) signals using a dual band receiver. Information about their path delay difference, yields information about the PWV in the ionosphere. The company has been actively investigating using the Russian Glonass system for some time, whereby it is hoped that a combination of GPS-Glonass technology will fulfil the requirements demanded by atmospheric monitoring equipment. Recent discussions have indicated the suitability of a dual band Glonass receiver for monitoring of L1-L2 path delays. The impact of new civilian frequencies on atmospheric modelling will be discussed. The application of GPS/Glonass technology to Meteorology brings environmental sensing into a new era. Improvements in surface, coastal and air travel safety will all be effected by more accurate predication of storm systems. A better understanding of microclimates will benefit agriculture by improving crop yields. This paper will outline the basic theory behind the monitoring of the atmosphere using GPS, detail both the GPS/Glonass technology in use as well as the atmospheric monitoring system used (MET3A from Paroscientific, Inc.). Recent developments and results will be presented, as will improvements necessary for successful and reliable civilian operation. A brief section on the benefits of, and future for, such technology will conclude the paper.
Published in:	Proceedings of the 2000 National Technical Meeting of The Institute of Navigation January 26 - 28, 2000 Pacific Hotel Disneyland Anaheim, CA
Pages:	490 - 494
Cite this article:	Percival, Richard, "The application of GPS/Glonass technology to atmospheric monitoring," Proceedings of the 2000 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 2000, pp. 490-494.
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