GRAV-D Project Update

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

• 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

Gravity for the Redefinition of the American Vertical Datum (GRAV-D)

January 10, 2012 2Federal Geodetic Control Subcommittee Meeting

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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)

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Federal Geodetic Control Subcommittee Meeting

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Ship gravity

Terrestrial gravity

New Orleans

20-100 km gravity gaps along coast

• 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

Problems with Gravity Holdings

GRAV-D Update

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Alaska FY8-12 West Coast FY11

Great Lakes FY11-13

FY8-10 = GreenFY11 = BlueFY12 = OrangeFY13 = White

FY12 Texas

15.6% of total area is

surveyed (as of 11-23-11)

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Federal Geodetic Control Subcommittee Meeting

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

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Pilatus PC-12King Air E-90A

Federal Geodetic Control Subcommittee Meeting

http://www.ngs.noaa.gov/GRAV-D/data_products.shtml

Data Distribution

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Federal Geodetic Control Subcommittee Meeting

http://www.ngs.noaa.gov/GRAV-D/data_products.shtml

Data Distribution

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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

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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

11January 10, 2012 Federal Geodetic Control Subcommittee Meeting

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

12January 10, 2012 Federal Geodetic Control Subcommittee Meeting

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

13January 10, 2012 Federal Geodetic Control Subcommittee Meeting

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

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Geoid Slope Validation Survey

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325 km218 points1.5 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

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