Geoid Height Models at NGS Dan Roman Research Geodesist.
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Transcript of Geoid Height Models at NGS Dan Roman Research Geodesist.
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Geoid Height Models at NGS
Dan RomanResearch Geodesist
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OUTLINE
• The GEOID team• What we produce• Next models• Ongoing research• The future
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The Geoid Team
• Primary Researchers– Daniel Roman, Ph.D.– Yan Ming Wang, Ph.D.
• Support– Gravity database & analysis: Jarir Saleh– Software & database: William Waickman
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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 …
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Global Relationships Between Geodetic Surfaces/Datums
Gravity Vector
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Local Relationships Between Geodetic Surfaces/Datums
Figure 2. Note the angular differences between the height vectors; termed the Deflection of the Vertical. For some specific applications, these can be significant (INS, etc.). Note also that the height relationship (h = H + N) is linearized – assuming that the angular differences can be neglected.
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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
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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
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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
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Extent of Gravity and Data Collection Flights
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Equivalent Pseudo-Geoid Signal for 91s Filter
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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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QUESTIONS?