Refinements to The World Geodetic System 1984

The World Geodetic System 1984 (WGS 84) is a Conventional Terrestrial Reference System that includes in its definition a reference frame, a reference ellipsoid, a consistent set of fundamental constants, and an Earth Gravitational Model (EGM) with a related global geoid. This DoD-developed reference system has evolved significantly since its creation in the mid-1980s and continues to provide a single, common, accessible 3- dimensional coordinate system for geospatial data collected from a broad spectrum of sources. Some of this geospatial data exhibits a high degree of 'metric' fidelity and requires a global reference frame which is free of any significant distortions or biases. For this reason, a series of improvements to WGS 84 were made in the past several years which served to refine the original version. Because these improvements are small in the context of mapping and charting, a complete redefinition of a new WGS is neither necessary nor desirable. The WGS 84 refinements which have been developed to date will be reviewed and explained. These include the development and implementation of two successive refined realizations of the WGS 84 reference frame, a review of the WGS 84 defining parameters and the development, with NASA/GSFC, of a new geopotential model known as the Earth Gravity Model 1996 (EGM 96). The accuracy of this gravity model and its associated global geoid will be discussed. Results from recent empirical comparisons between the WGS 84 reference frame and the International Terrestrial Reference Frame (ITRF) will also be presented.