Vertical Ocean-loading Deformations Derived from a Global GPS Network.

Abstract

The proliferation of permanent Global Positioning System (GPS) tracking sites and improvements in estimating the vertical component of a site's coordinates from GPS measurements present an opportunity to directly observe the crustal deformation caused by loading from ocean tides. The long, continuous record from these sites enables the accumulation of observations coherently with respect to the driving tidal forces, and estimates of the ocean-loading signal can be made from these accumulated observations. Techniques like this defeat atmospheric, geometrical, and multipath effects which can have a comparable magnitude, but do not have the same period as ocean-loading. A project to estimate ocean-loading effects at sites globally was undertaken at the Geodetic Research Division of the National Geodetic Survey. The technique used in and results of that project are presented here. Emphasis will be placed on the diurnal and semi-diurnal tidal signals. Although excellent agreement with existing models is found for most sites, a large fraction, generally those at higher latitudes where the complex coastlines and poorer ocean tidal data begin to dominate, show significant differences from standard ocean-loading models.