The National Geodetic Survey Gravity Program Benefits and Opportunities Juliana Blackwell, Director National Geodetic Survey (NGS)

What is Geodesy? Geodesy (geodetic control) is a foundational science that defines position and height. The Earth is an irregular surface and is difficult to model. Accurate positions are required for a wide variety of applications. Why is Geodesy important? January 23, 20122MAPPS 2012 Winter Conference

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. January 23, 20123MAPPS 2012 Winter Conference

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NGS Provides the Geospatial Foundation for a Wide Variety of Activities Geodetic Control Aerial Imagery Elevation Boundaries Surface Waters Transportation Land Ownership January 23, 20126MAPPS 2012 Winter Conference

The NSRS Supports: 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 NSRS gravity data for the geospatial mission of NGA National Geospatial-Intelligence Agency Topographic Maps and interior water data for the nation United States Geological Survey Nautical charts, among many other geospatial applications National Oceanic and Atmospheric Administration January 23, 20127MAPPS 2012 Winter Conference

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 "topographic map." Online Art. Britannica Student Encyclopædia. 17 Dec January 23, 20128MAPPS 2012 Winter Conference Vertical Datum 101

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* – 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 Helmert orthometric 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 January 23, 20129MAPPS 2012 Winter Conference

H Earth’s Surface The Geoid NAVD 88 reference level H (NAVD 88) Errors in NAVD 88 : ~50 cm average, 100 cm CONUS tilt, 1-2 meters average in Alaska, NO tracking of temporal changes Errors in NAVD 88 January 23, MAPPS 2012 Winter Conference

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 Gravity for the Redefinition of the American Vertical Datum (GRAV-D) January 23, 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 Surface Measurement Short Wavelengths (< 100 km) + + January 23, 2012MAPPS 2012 Winter Conference

Geoid Slope Validation Survey January 23, 2012MAPPS 2012 Winter Conference km 218 points 1.5 km apart Austin Rockport 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

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 January 23, 2012MAPPS 2012 Winter Conference14

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

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 16January 23, 2012MAPPS 2012 Winter Conference

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 17January 23, 2012MAPPS 2012 Winter Conference

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 18January 23, 2012MAPPS 2012 Winter Conference