In addition to the science-enabling role played by the precise knowledge of GPS transmitter positions, a direct science benefit also comes from JPL's regular analysis of data from terrestrial GPS receivers. In the early 1990s, only a few tens of receivers were in regular operation, and the computational burden associated with their analyses was tractable, even with primitive (by today's standards) computing resources. JPL has been able to keep up with the explosive growth in the terrestrial GPS receiver network because of advances in the relevant information technology as well as availability of vast computing resources at low cost. Currently it is typical for data from over 500 sites to be analyzed every day.
Jim Zumberge and Michael Heflin