Geoid Height Models at ngs dan Roman Research Geodesist

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Geoid Height Models at NGS

  • Dan Roman

  • Research Geodesist


  • The GEOID team

  • What we produce

  • Next models

  • Ongoing research

  • The future

The Geoid Team

  • Primary Researchers

    • Daniel Roman, Ph.D.
    • Yan Ming Wang, Ph.D.
  • Support

    • Gravity database & analysis: Jarir Saleh
    • Software & database: William Waickman

What We Produce: Geoid Height Models

  • Q: So what’s a “geoid height” model?

  • A: A model of the separation between a geoid or vertical datum and an ellipsoidal datum.

  • Q: The separation between a what and a what?!

  • A: OK … maybe a brief GEOID 101 tutorial to cover the basics …

Global Relationships Between Geodetic Surfaces/Datums

Local Relationships Between Geodetic Surfaces/Datums

What else is produced?

  • Deflection of the Vertical

    • Derived from geoid height model
    • Angle between normals to ellipsoid & geoid
    • Useful in navigation functions
  • Surface Gravity Interpolation

Models Under Development


  • USGG2006: CONUS

    • Validation of reference field used (GRACE)
    • Already see a half cm improvement nationally when comparing to the GPSBM’s
    • Incorporation of coastal aerogravity study
    • Comparison at tide gauges and with VDatum

Near Term Research

  • Assessing impact of aerogravity in coastal regions

  • Utility of GPS/INS vs. aerogravity for gravity

  • Assessment of EGM06 and GRACE-based gravity

  • Temporal effects in gravity and geoid

  • Seamless & accurate gravity data set

  • Improved theory for determining geoid height models from gravity data

  • Monte Carlo study of current gravimetric geoid height model

  • Error propagation to estimate hybrid geoid errors

Extent of Gravity and Data Collection Flights

Equivalent Pseudo-Geoid Signal for 91s Filter

Long Term Goals

  • Orthometric heights determined from a cm-level accurate gravimetric geoid applied to cm-level accurate GPS-derived ellipsoidal heights

  • An error model of the existing NAVD 88 datum

  • A unifying datum common to all interested countries in the hemisphere (Canada, Mexico, other North & Central American countries, and Caribbean nations).

  • A common basis for an IGLD15 model


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