Measuring the earth to within an inch using GPS satellites

A recently developed technique for “measuring the Earth” was demonstrated in 1991 using data from an experiment involving a world-wide network of receivers that track satellites of the Global Positioning System (GPS). Recent results indicate that distances between points separated by as much as 10,000 km on the surface of the Earth can be determined at the 2 cm level, and that the position of the pole of rotation at the Earth's surface can be estimated daily to better than 2 cm. Achieving this level of accuracy in a reliable, economical way is an important step towards building our understanding of the Earth as a rotating, deforming body. Funded by NASA's Solid Earth Science Program, the Jet Propulsion Laboratory coordinated participation of many international institutions in a 3-week experiment in January–February 1991 called GPS for International Earth Rotation Service (IERS) and Geodynamics '91 (GIG'91). Twenty-one receivers developed by J PL and scores of commercial receivers were simultaneously deployed. Several independent groups around the world analyzed the data and presented results at meetings in the summer and fall of 1991.