The Global Positioning System (GPS) is the most recent entry into the field that has become known as “space geodesy.” GPS holds great promise for obtaining inexpensive, high-accuracy terrestrial surveys with applications in a number of diverse geophysical disciplines. This wide applicability makes GPS surveying of interest to researchers throughout the geophysical and geodetic spectrum.

Because GPS is perceived as a “hands-on” technique, the actual surveying and subsequent data analysis are often left to the geoscientists interested in interpreting the results. This has led to some unexpected difficulties, for the analysis of GPS data is really two quite separate tasks. On the one hand, there is the problem of modeling time-series of three-dimensional intersite vectors in terms of geophysically interesting quantities. Before this, however, one must solve for the intersite vectors themselves using the “raw” GPS phase observables, a nontrivial operation.