Geodesy
Fundamentals Geodesy Geodynamics Geomatics History
Concepts Geographical distance Geoid Figure of the Earth (radius and circumference) Geodetic coordinates Geodetic datum Geodesic Horizontal position representation Latitude / Longitude Map projection Reference ellipsoid Satellite geodesy Spatial reference system Spatial relations Vertical positions
Technologies Global Nav. Sat. Systems (GNSSs) Global Pos. System (GPS) GLONASS (Russia) BeiDou (BDS) (China) Galileo (Europe) NAVIC (India) Quasi-Zenith Sat. Sys. (QZSS) (Japan) Discrete Global Grid and Geocoding
Standards (history) NGVD 29 Sea Level Datum 1929 OSGB36 Ordnance Survey Great Britain 1936 SK-42 Systema Koordinat 1942 goda ED50 European Datum 1950 SAD69 South American Datum 1969 GRS 80 Geodetic Reference System 1980 ISO 6709 Geographic point coord. 1983 NAD 83 North American Datum 1983 WGS 84 World Geodetic System 1984 NAVD 88 N. American Vertical Datum 1988 ETRS89 European Terrestrial Ref. Sys. 1989 GCJ-02 Chinese obfuscated datum 2002 Geo URI Internet link to a point 2010 International Terrestrial Reference System Spatial Reference System Identifier (SRID) Universal Transverse Mercator (UTM)
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The North American Vertical Datum of 1988 (NAVD 88) is the vertical datum for orthometric heights established for vertical control surveying in the United States of America based upon the General Adjustment of the North American Datum of 1988.^[1]

It superseded the National Geodetic Vertical Datum of 1929 (NGVD 29),^[2] previously known as the Sea Level Datum of 1929.

NAVD 88, along with North American Datum of 1983 (NAD 83), is set to be replaced in 2025 with a new geometric reference frame and geopotential datum, based on GPS and gravimetric geoid models.^[3]

Methodology

NAVD 88 was established in 1991 by the minimum-constraint adjustment of geodetic leveling observations in Canada, the United States, and Mexico. It held fixed the height of the primary tide gauge benchmark, referenced to the International Great Lakes Datum of 1985 local mean sea level (MSL) height value, at Rimouski, Quebec, Canada. Additional tidal bench mark elevations were not used due to the demonstrated variations in sea surface topography, i.e., that MSL is not the same equipotential surface at all tidal bench marks.^[1]

North American Vertical Datum of 1988 (NAVD 88) consists of a leveling network on the North American Continent, ranging from Alaska, through Canada, across the United States, affixed to a single origin point on the continent.^[1]

In 1993 NAVD 88 was affirmed as the official vertical datum in the National Spatial Reference System (NSRS) for the Conterminous United States and Alaska.^[4] (see Federal Register Notice (FRN)). Although many papers on NAVD 88 exist, no single document serves as the official defining document for that datum.^[1]

The definition of NAVD 88 uses the Helmert orthometric height, which calculates the location of the geoid (which approximates MSL) from modeled local gravity.^{[citation needed]} The NAVD 88 model is based on then-available measurements, and remains fixed despite later improved geoid models.^{[citation needed]}

Since NGVD 29 used a simple model of gravity based on latitude to calculate the geoid and did not take into account other variations,^{[citation needed]} elevation difference between points in a local area in it and NAVD 88 will show negligible change from one datum to the other, even though the elevation of both does change between datums.^{[citation needed]}

Datum of 2022

Based on the more recent surveying techniques and data, it was determined that NAVD 88 is both biased (by about 0.5 meters (1 ft 8 in)) and tilted (about 1 meter (3 ft 3 in) coast to coast).^[5] To improve the National Spatial Reference System (NSRS), the National Geodetic Service will replace the North American Datum of 1983 (NAD 83) and the North American Vertical Datum of 1988 (NAVD 88) with a new geometric reference frame and geopotential datum in 2025.^[3][6]

The new reference frames will rely primarily on Global Navigation Satellite Systems (GNSS), such as the Global Positioning System (GPS), as well as on a gravimetric geoid model resulting from NOAA's Gravity for the Redefinition of the American Vertical Datum (GRAV-D) Project. These new reference frames are intended to be easier to access, and maintain, than NAD 83 and NAVD 88, which rely on physical survey marks that deteriorate over time.^[3]