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GRAV-D Project Update

Replace the USA's vertical datum by 2022 with a gravimetric geoid accurate to 1 cm and GNSS-based orthometric heights accurate to 2 cm. This update includes airborne gravity surveys, long-term geoid change monitoring, and partnership surveys.

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GRAV-D Project Update

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  1. GRAV-D Project Update Vicki Childers, Ph.D. GRAV-D Project Manager

  2. 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 accurate to 2 cm • 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 Federal Geodetic Control Subcommittee Meeting

  3. 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 Federal Geodetic Control Subcommittee Meeting

  4. Problems with Gravity Holdings 20-100 km gravity gaps along coast Terrestrial gravity • Field is not sampled uniformly • Data range in age and quality, some w/o metadata • Some surveys have systematic errors • Data gaps in littoral areas Ship gravity New Orleans Federal Geodetic Control Subcommittee Meeting

  5. GRAV-D Update Alaska FY8-12 West Coast FY11 15.6% of total area is surveyed (as of 11-23-11) FY8-10 = Green FY11 = Blue FY12 = Orange FY13 = White Great LakesFY11-13 FY12 Texas Federal Geodetic Control Subcommittee Meeting

  6. GRAV-D Aircraft • NOAA • Gulfstream Jet Prop • NOAA P-3 Hurricane Hunter • DOI Bureau of Land Management • Pilatus PC-12 • Fugro • King Air E-90A • Naval Research Lab • King Air RC-12 Pilatus PC-12 King Air E-90A Federal Geodetic Control Subcommittee Meeting

  7. Data Distribution http://www.ngs.noaa.gov/GRAV-D/data_products.shtml Federal Geodetic Control Subcommittee Meeting

  8. Data Distribution http://www.ngs.noaa.gov/GRAV-D/data_products.shtml Federal Geodetic Control Subcommittee Meeting

  9. Data Products • Detailed map of region • Data download link to zip file: • ReadMe text file • gravity data file • supplementary data file • block data user manual • GRAV-D data general user manual • xml metadata • kml block extent and block data lines. • Gridded image of gravity data • Older versions if available Federal Geodetic Control Subcommittee Meeting

  10. Future Contracting Plans • Minimum of 10% of annual surveying will be contracted out (~100 flight hours/yr) • Contract Aircraft Services • FY11 Fugro: 10.7% • FY12 Fugro (estimated): 20.6% • If additional funding can be found, the percentage of contract surveying would be increased • Explore options for dedicated aircraft enabled for magnetic measurement Federal Geodetic Control Subcommittee Meeting

  11. GRAV-D Federal Partnerships • Department of Interior • Bureau of Land Management: shared use of Pilatus aircraft • US Geological Survey: launching effort to collect simultaneous magnetic measurements • Naval Research Laboratory • VXS-1 Squadron aircraft services • National Geospatial-Intelligence Agency (NGA) • Funded AK survey in 2009 • Absolute and relative gravimetry coordination Federal Geodetic Control Subcommittee Meeting

  12. 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 Federal Geodetic Control Subcommittee Meeting

  13. 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 Federal Geodetic Control Subcommittee Meeting

  14. 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 Federal Geodetic Control Subcommittee Meeting

  15. 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 Federal Geodetic Control Subcommittee Meeting

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