Atmospheric Pressure Loading and its Effects on Precise Point Positioning

L. Urquhart

Abstract:	As the precision of space geodetic techniques improve many trends or unwanted noise can be observed in the geodetic time series that were at one time considered negligible. The first users to be affected by these trends in the time series are those using the most precise techniques such as VLBI and SLR. With the improvement of GNSS technology, as well as precise orbit and clock products from the IGS, many of these same errors have become visible in GNSS time series derived using the technique of PPP. Atmospheric pressure loading is the displacement of the earth's crust as a result of the movement of pressure systems over the Earth. While this effect has been known for a long time, it is only recently that it can be detected using space geodetic techniques. Occasionally, these displacements can reach 2-3 centimeters in the vertical direction due to the movement of pressure systems over the earth. Since this is within the realm of precision for PPP it is hypothesized that the atmospheric loading signal will be visible in the PPP time series. A global set of 8 stations were selected and processed for one year using the PPP technique. These time series were then corrected for atmospheric loading using both the geophysical approach and the empirical approach to model the crustal displacement. For the empirical approach the local pressure values were obtained from site VMF1 data as suggested by Kouba [2008]. The variance of the PPP solutions was in most cases several orders of magnitude larger than the variance of the atmospheric loading corrections. In total, six out of the eight stations saw a reduction in the RMS after the geophysical model was applied while only five stations saw a reduction when the empirical model was used. The reductions were small for all stations, approximately 3.6 and 5.9 percent for the geophysical and empirical model respectively. On average this translates into approximately 2-3 mm reduction in scatter for the time series. As PPP techniques improve the benefits of applying the atmospheric loading correction should become more pronounced. At this time, the inclusion of atmospheric pressure loading corrections into routine PPP processing does not seem necessary. However, for studies that examine other pressure related parameters, atmospheric pressure loading corrections should be considered.
Published in:	Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009) September 22 - 25, 2009 Savannah International Convention Center Savannah, GA
Pages:	658 - 667
Cite this article:	Urquhart, L., "Atmospheric Pressure Loading and its Effects on Precise Point Positioning," Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009), Savannah, GA, September 2009, pp. 658-667.
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