Effects of atmospheric pressure loading on GPS measurements

Abstract

With millimeter-level positioning capabilities, annual fluctuations in GPS height estimates can now be resolved. A likely explanation for these height variations is loading of the Earth's surface. We examine the relative contribution of atmospheric pressure loading to the total signal by modeling loads utilizing Farrell's elastic Green's functions. A focus on four permanent GPS sites provided insight on coastal and seasonal differences as well as the relative impact of atmospheric pressure loading on annual vertical displacements. Our findings suggest that accounting for the inverted barometer response [Farrell, 1972] of the ocean at coastal sites provides a better fit to GPS data. However, near restricted bodies of water we find that the non-inverted barometer fits better. We also found lower closer fits of the modeled pressure load to the GPS data during winter months than during the summer possibly due to larger pressure variations during the winter and/or mismodeling of tropospheric delay during summer months [Herring, 1990]. As for the contribution due to multiple sources of loading, in most cases, by adding an expected water load (from upper 2 meters of soil) to the atmospheric pressure load, a closer agreement to the GPS signal was found.