Geoid12B

Geoid12B
Name	Geoid12B
Type	geoid model
Developer	National Geospatial-Intelligence Agency/National Oceanic and Atmospheric Administration (U.S.)
Release	2012
Latest	Geoid12B
Area	United States
Resolution	1 arc-minute
Datum	North American Vertical Datum of 1988

Geoid12B Geoid12B is a gravitational equipotential surface model producing a geopotential-derived height reference for the United States Department of Defense and civilian mapping. It provides a national vertical datum transformation for agencies such as the National Geodetic Survey and the United States Geological Survey to relate orthometric heights to ellipsoidal heights derived from Global Positioning System. Developed in 2012, it succeeded earlier models and informed work by the Federal Emergency Management Agency and U.S. Army Corps of Engineers in flood mapping and infrastructure projects.

Overview

Geoid12B represents the separation between the Geodetic Reference System 1980 ellipsoid and mean sea level as modeled by the Earth's gravity field over the United States and surrounding waters. The model uses spherical harmonic and tesseroid techniques pioneered by organizations like the National Aeronautics and Space Administration and the European Space Agency while aligning with operational needs of the Department of Commerce and the Department of Defense. Geoid12B enabled improved interoperability among agencies including the Federal Aviation Administration, Bureau of Land Management, National Park Service, and United States Forest Service.

Development and Methodology

Geoid12B was produced through collaboration among the National Geodetic Survey, National Oceanic and Atmospheric Administration, and contractors with expertise from academic centers such as Massachusetts Institute of Technology, Ohio State University, and University of Colorado Boulder. Methodologies combined long-wavelength gravity field information from satellite missions like GRACE and GOCE with terrestrial and airborne gravimetry collected by the National Geospatial-Intelligence Agency and U.S. Geological Survey. Processing workflows borrowed algorithms from the International Association of Geodesy studies and applied least-squares collocation, spherical harmonic synthesis, and remove-restore strategies common to models developed by the Jet Propulsion Laboratory.

Data Sources and Processing

Primary inputs included airborne gravimeter surveys conducted by the U.S. Army Corps of Engineers, shipborne gravity profiles from the National Oceanic and Atmospheric Administration, and ground gravity stations archived by the International Gravimetric Bureau. The model integrated ellipsoidal heights from Global Positioning System continuous operating reference stations and leveling networks maintained by the National Geodetic Survey. Data processing involved noise filtering, datum unification to North American Datum of 1983, and gravity anomaly reduction techniques standardized by the International Union of Geodesy and Geophysics. Quality control referenced benchmarks from the United States Coast and Geodetic Survey and used cross-validation against tide gauge records maintained by the National Ocean Service.

Accuracy and Validation

Validation of Geoid12B employed crosschecks with independent leveling transects from the United States Geological Survey and precise GNSS campaigns conducted by universities including University of Texas at Austin and Pennsylvania State University. Reported root-mean-square errors varied regionally due to crustal heterogeneity and data density, with coastal zones validated against tide gauge observations and interior regions compared to gravimetric models used by the U.S. Army Engineer Research and Development Center. Peer reviews cited in technical memoranda involved panels from the National Academy of Sciences and practitioners from the American Society of Civil Engineers.

Applications

Geoid12B supported orthometric height determination for surveying projects by the National Geodetic Survey, levee certification by the Federal Emergency Management Agency, coastal resilience planning by the National Oceanic and Atmospheric Administration, and aviation instrument procedures managed by the Federal Aviation Administration. It informed floodplain mapping used by the Federal Emergency Management Agency and infrastructure design performed by the U.S. Army Corps of Engineers and state departments of transportation such as the California Department of Transportation and Texas Department of Transportation. Academic research in geophysics at institutions like Harvard University and Stanford University also used Geoid12B for crustal studies.

Limitations and Criticism

Critiques of Geoid12B focused on spatial resolution limits relative to local engineering needs, differences with subsequent models produced by the National Geodetic Survey, and sensitivity to errors in input gravity data from sparse regions such as the Arctic and off-shore areas. Stakeholders including state surveying offices and professional bodies like the National Society of Professional Surveyors noted that residual discrepancies required supplemental local surveys. Comparative analyses with later products highlighted the need for denser airborne gravimetry and integration with newer satellite missions to reduce regional biases identified by researchers at the Scripps Institution of Oceanography.

Adoption and Implementation

Adoption of Geoid12B occurred across Federal agencies, state geodetic surveys, and private surveying firms implementing height conversions in digital elevation models and geospatial information systems provided by vendors like Esri. Implementation tools included lookup grids, conversion software distributed by the National Geodetic Survey, and web services used by the Federal Geographic Data Committee and state geospatial portals. Transition plans coordinated by the National Oceanic and Atmospheric Administration and Department of Commerce guided users to newer models while documenting procedures for legacy data compatibility.

Category:Geodesy