Differential GPS (dGPS) is a technique that provides extremely accurate location data, up to 100 times more accurate than GPS alone.

A Brief History of dGPS

Because GPS was originally intended for the use of the U.S. military, it was built with a feature called Selective Availability, which, when activated, can introduce random errors of up to 100 meters. These errors were meant to prevent any potential adversaries from using GPS against the U.S. (to target missiles, for example). In addition to the SA errors, GPS was (and is today) subject to other errors introduced by satellite ephemeris, clock errors, ionospheric distortions, and tropospheric distortions. dGPS was created to provide more accurate data by correcting for these errors.

dGPS accomplishes this correction by using ground-based reference stations in fixed, known-position locations which receive GPS satelllite data, correct for these errors, and broadcasting the corrected data to roving GPS units capable of receiving them (a dGPS beacon receiver is required). This provides much greater accuracy for navigation, agriculture, GIS and other industrial and consumer needs.

In 2000, Selective Availability was turned off by executive order. With SA turned off GPS receivers can provide accurate location data to within about 10 meters. While 10 meters was a great improvement, it still didn't meet the higher precision needed for marine navigation, air navigation, GIS or many other industrial and consumer needs. dGPS has continued to evolve to meet the ever more demanding accuracy needs of both industry and consumers.