Geoid Height Models at ngs dan Roman Research Geodesist

Geoid Height Models at NGS

• Dan Roman

• Research Geodesist

OUTLINE

• 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

• Provides a point estimate of surface gravity
• Used in sensitive engineering applications
• Also used in some scientific studies of tides

Models Under Development

• GEOID06: CONUS, PR/VI

• CONUS data reflect pre-NRA solution
• Pull complete: nearly 18,000 points
• PR/VI will be tied to PRVD 02 model (hybrid)

• 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

QUESTIONS?