The National Geodetic Survey Gravity Program Benefits and Opportunities

1. The National Geodetic Survey Gravity ProgramBenefits and Opportunities Juliana Blackwell, Director National Geodetic Survey (NGS)

2. What is Geodesy? Geodesy (geodetic control) is a foundational science that defines position and height. Why is Geodesy important? The Earth is an irregular surface and is difficult to model. Accurate positions are required for a wide variety of applications. MAPPS 2012 Winter Conference

3. NGS Mission Statement To define, maintain and provide access to the National Spatial Reference System (NSRS) to meet our nation’s economic, social, and environmental needs. The NSRS is a consistent coordinate system that defines latitude, longitude, height, scale, gravity, and orientation throughout the United States. MAPPS 2012 Winter Conference

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6. Land Ownership Transportation Surface Waters Boundaries Elevation Geodetic Control Aerial Imagery NGS Provides the Geospatial Foundation for a Wide Variety of Activities MAPPS 2012 Winter Conference

7. The NSRS Supports: Nautical charts, among many other geospatial applications National Oceanic and Atmospheric Administration Flood zones for the National Flood Insurance Program Federal Emergency Management Agency Levee Safety Program to determine levee heights and positions United States Army Corps of Engineers Topographic Maps and interior water data for the nation United States Geological Survey NSRS gravity data for the geospatial mission of NGA National Geospatial-Intelligence Agency MAPPS 2012 Winter Conference

8. "topographic map." Online Art. Britannica Student Encyclopædia. 17 Dec. 2008   <http://student.britannica.com/ebi/art-53199> Vertical Datum 101 • Strictly speaking, a vertical datum is a surface representing zero elevation • A vertical datum has a: • Definition: Parameters and other descriptors • Realization: Its physical method of accessibility • Traditionally, how heights above the datum are determined is also specified • Orthometric vs. dynamic MAPPS 2012 Winter Conference

9. NGS and the National Vertical Datum NAVD 88 (North American Vertical Datum of 1988) • Definition: • The surface of equal gravity potential to which orthometric heights shall refer in North America* • 6.271 meters (along the plumb line) below the geodetic mark at “Father Point/Rimouski” (NGSIDB PID TY5255) • Realization: • Over 500,000 geodetic marks across North America with published Helmertorthometric heights • Most heights were originally computed from a minimally constrained adjustment of leveling and gravity data, holding the geopotential value at “Father Point/Rimouski” fixed. Father Point Lighthouse Quebec *Not adopted in Canada MAPPS 2012 Winter Conference

10. Errors in NAVD 88 Earth’s Surface H (NAVD 88) H NAVD 88 reference level The Geoid Errors in NAVD 88 : ~50 cm average, 100 cm CONUS tilt, 1-2 meters average in Alaska, NO tracking of temporal changes MAPPS 2012 Winter Conference

11. Gravity for the Redefinition of the American Vertical Datum (GRAV-D) • Replace the Vertical Datum of the USA by 2022 (at today’s funding) with a gravimetric geoid accurate to 1 cm • Orthometric heights accessed via GNSS • Three thrusts of project: • Airborne gravity survey of entire country and its holdings • Long-term monitoring of geoid change • Partnership surveys • Working to launch a collaborative effort with the USGS for simultaneous magnetic measurement • Big benefits: $522 million in estimated annual economic benefits once complete MAPPS 2012 Winter Conference

12. Building a Gravity Field Long Wavelengths: (≥ 350 km) GRACE and GOCE (not shown) + Intermediate Wavelengths (500 km to 20 km) Airborne Measurement + Short Wavelengths (< 100 km) Surface Measurement MAPPS 2012 Winter Conference

13. Geoid Slope Validation Survey • Observe geoid shape (slope) using multiple independent terrestrial survey methods • GPS + Leveling • Deflections of the Vertical • Compare observed slopes (from terrestrial surveys) to modeled slopes (from gravimetry or satellites) • With/without new GRAV-D airborne gravity Austin 325 km 218 points 1.5 km apart Rockport MAPPS 2012 Winter Conference

14. Geoid Slope Survey Conclusions • Including airborne gravity data improves geoid slope accuracy at nearly all distances <325 km • The NGS geoid in the TX survey meets the 1 cm accuracy objective only if airborne data are included • No other model achieved 1 cm accuracy • Gravimetric geoid models and GPS are a viable alternative to long-line leveling MAPPS 2012 Winter Conference

15. GRAV-D Update Alaska FY10-13 West Coast FY11 15.6% of total area is surveyed (as of 11-23-11) FY10 = Green FY11 = Blue FY12 = Orange FY13 = White Great LakesFY11-13 FY12 Texas MAPPS 2012 Winter Conference

16. GRAV-D Contracting Expenditures • Contract employees: • FY11: 24.5% of total expenditures • FY12 (planned): 24.8% • Contract Surveys • FY11 Fugro: 10.7% • FY12 Fugro (estimated): 20.6% • Fugro • Provided aircraft and operator in FY11 • Exploring option for data products in FY12 MAPPS 2012 Winter Conference

17. Future Contracting Plans • Minimum of 10% of annual surveying will be contracted out (~100 flight hours/yr) • If additional funding can be found, the percentage of contract surveying would be increased • Explore options for dedicated aircraft enabled for magnetic measurement MAPPS 2012 Winter Conference

18. Summary • GRAV-D project is on course for completion in 2022 • Involvement with contract data services is planned at the 10% level minimum • The new vertical datum produced by this effort will be invaluable for all geospatial concerns MAPPS 2012 Winter Conference