Evolution of NAD 83 in the United States: Journey from 2D toward 4D

Abstract

In 1986, Canada, Greenland, and the United States adopted the North American Datum of 1983 (NAD 83) to replace the North American Datum of 1927 as their official spatial reference system for geometric positioning. The rigor of the original NAD 83 realization benefited from the extensive use of electronic distance measuring instrumentation and from the use of both TRANSIT Doppler observations and very long baseline interferometry observations. However, the original NAD 83 realization predated the widespread use of the global positioning system and the use of continuously operating reference stations. Consequently, NAD 83 has evolved significantly in the United States since 1986 to embrace these technological advances, as well as to accommodate improvements in the understanding of crustal motion. This paper traces this evolution from what started as essentially a two-dimensional (2D) reference frame and has been progressing toward a four-dimensional (4D) frame. In anticipation of future geodetic advances, the U.S. National Geodetic Survey is planning to replace NAD 83 about a decade from now with a newer, more geocentric spatial reference system for geometric positioning.