EGM2008

EGM2008
Name	EGM2008
Type	Geoid model
Developer	National Geospatial-Intelligence Agency, National Oceanic and Atmospheric Administration, Ohio State University, NASA
Release	2008
Resolution	2.5′ (~5 km)
Maximum degree	2190
Mass market	Global
License	Public domain (U.S. government works)

EGM2008 is a global geopotential and geoid model released in 2008 that provides a high-resolution representation of Earth's equipotential surface used to relate mean sea level to a reference ellipsoid and to convert between ellipsoidal heights and orthometric heights. The model integrates satellite, altimetry, and terrestrial gravity data to produce a geopotential model to spherical harmonic degree 2190 with coefficients suitable for precise geodetic, oceanographic, and geophysical applications. EGM2008 was produced through a collaboration among U.S. federal agencies and academic institutions and has become widely used by organizations requiring centimeter-to-decimeter level vertical control worldwide.

Overview

EGM2008 presents a global geopotential solution with spherical harmonic coefficients to degree and order 2190, yielding a nominal spatial resolution of approximately 2.5 arc minutes that corresponds to about 5 kilometers at the equator. The model links to geodetic reference frames such as World Geodetic System 1984 and supports transformations involving ellipsoids like the WGS 84 ellipsoid and the GRS 80 ellipsoid. Intended consumers include national mapping agencies such as the Ordnance Survey, Institut Géographique National, and United States Geological Survey, as well as scientific organizations like European Space Agency and Intergovernmental Oceanographic Commission.

Development and Methodology

Development was led by the National Geospatial-Intelligence Agency and National Oceanic and Atmospheric Administration with academic partners including Ohio State University and researchers affiliated with NASA. The methodology combined spherical harmonic synthesis, remove-restore techniques, and least-squares collocation to merge disparate datasets. Computational techniques invoked linear algebra libraries and high-performance computing resources similar to those used in projects at Lawrence Livermore National Laboratory and Jet Propulsion Laboratory. Quality control procedures referenced practices from organizations such as International Association of Geodesy and International Hydrographic Organization.

Data Sources and Resolution

EGM2008 assimilated satellite gravity data from missions including GRACE (satellite mission), satellite altimetry datasets from missions like TOPEX/Poseidon and Jason-1, airborne and shipboard gravimetry collected by agencies such as NOAA and British Antarctic Survey, and terrestrial gravity measurements archived by the International Gravimetric Bureau. The model also used digital elevation models like ETOPO1 and topographic information from national mapping agencies including Geoscience Australia. The inclusion of high-degree spherical harmonics up to 2190 yields a fine-scale representation limited primarily by data coverage in polar and inland regions, with effective resolution influenced by noise characteristics from sources such as GOCE (predecessor/successor mission data comparisons).

Applications and Uses

EGM2008 supports geodetic height conversion for surveying projects undertaken by institutions like National Geodetic Survey and urban infrastructure planners in municipalities comparable to City of New York or Greater London Authority. Oceanographers working at Scripps Institution of Oceanography and Woods Hole Oceanographic Institution use the model for mean sea surface and ocean circulation studies, while climate scientists at NOAA Climate Program Office integrate geopotential data in mass transport analyses linked to sea level rise. Geophysicists apply the model in lithospheric studies for regions monitored by observatories such as USGS Volcano Hazards Program and institutes like GFZ German Research Centre for Geosciences.

Accuracy, Errors, and Validation

Validation efforts compared EGM2008 output against independent gravity and height control datasets from the International Height Reference System and national leveling networks administered by agencies such as Canadian Geodetic Survey and Geodetic Institute of Finland. Error characteristics exhibit spatial variability: coastal and well-surveyed continental regions show centimeter-level agreement, whereas sparsely sampled polar areas and parts of ocean basins reveal larger residuals. Systematic errors can arise from datum inconsistencies among datasets maintained by institutions like Russian Federal Service for State Registration and historical surveys by U.S. Coast and Geodetic Survey. Cross-validation with satellite missions including GRACE and GOCE helped quantify long-wavelength errors and degree variances.

Relationship to Other Geopotential Models

EGM2008 is a successor to earlier geopotential models such as models developed by the U.S. Department of Defense and academic efforts prior to 2000, and it complements satellite-only models like those produced from GRACE and GOCE data. Regional high-resolution quasigeoid models from national agencies—examples include models produced by Netherlands’ Kadaster and Japanese Geospatial Information Authority—may offer higher local fidelity than the global model for specific applications. Comparison metrics often reference spherical harmonic degree spectra and geoid height differences previously used in assessments by the International Association of Geodesy.

Availability and Implementation Settings

EGM2008 coefficients, gravitational potential grids, and geoid height grids were distributed by the developing agencies in machine-readable formats compatible with geodetic software such as PROJ, GeographicLib, and GEOID Toolbox implementations in environments used by researchers at institutions like MIT and Stanford University. Typical implementation settings specify using the spherical harmonic coefficients to degree 2190 with associated normalization conventions and employing tide-free or zero-tide systems consistent with national coordinate practices of agencies like Ordnance Survey of Northern Ireland and Instituto Geográfico Nacional (Spain). Users should select appropriate units, normalization, and tide systems to match local vertical datum transformations.

Category:Geodesy