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GRAV-D Part I: NGS’ Gravity for the Re-definition of the American Vertical Datum Project

GRAV-D Part I: NGS’ Gravity for the Re-definition of the American Vertical Datum Project. V. A. Childers, D. R. Roman, D. A. Smith, and T. M. Diehl* U.S. National Geodetic Survey. Overview. NAVD 88 A new American vertical datum Gravity and the geoid GRAV-D plan

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GRAV-D Part I: NGS’ Gravity for the Re-definition of the American Vertical Datum Project

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  1. GRAV-D Part I: NGS’ Gravity for the Re-definition of the American Vertical Datum Project V. A. Childers, D. R. Roman, D. A. Smith, and T. M. Diehl* U.S. National Geodetic Survey

  2. Overview • NAVD 88 • A new American vertical datum • Gravity and the geoid • GRAV-D plan • Airborne surveys completed • Plans for FY10 and beyond

  3. The Current Vertical Datum: NAVD 88 1807 – 1996 • Defined and Accessed – Leveling/Passive Marks • Currently: North American Vertical Datum 1988 • NAVD 88: 600,000+ Marks • NGS detects hundreds moved/destroyed every year • How many go undetected? • Post-Glacial-Rebound, Subsidence, Tectonics, Frost-Heave – lots of motion out there!

  4. Errors in NAVD 88 • NAVD 88 H=0 level is known not to be the geoid • Average 1 m bias and 1 m tilt across CONUS • 1-2 m bias in Alaska Difference: NAVD 88 – datum derived from GRACE Min = 0.17 m Max = 1.88 m Ave = 0.98 m Std. Dev. = 0.37 m

  5. New Datum Requirements in the Age of Space-based Geodesy • The GPS era brought fast, accurate ellipsoid heights – naturally this drove a desire for fast, accurate orthometric heights • 1-2 cm accuracy is needed • Leveling the country can not be done again • Too costly in time and money • Leveling yields cross-country error build-up • Leveling requires leaving behind marks • Bulldozers and crustal motion do their worst

  6. NGS’ Plan: GRAV-D • Official NGS policy: • Re-define the US Vertical Datum by creating a new gravimetric geoid • 10 year program • Two Major Program Elements • Airborne Gravity “Snapshot” for Baseline • Long Term Monitoring of Temporal Changes • Projected program cost: $38.5M over 10 years

  7. Static Snapshot: Airborne • Provides intermediate wavelength gravity data • Reconciles terrestrial datasets • Fills in spatial gaps in the littoral region Terrestrial gravity points 20-100 km gravity gaps along coast Ship gravitytracks New Orleans

  8. Monitoring Change: Terrestrial • Uplift: tectonic, GIA • Subsidence: sediment compaction, tectonic, water/oil pumping, GIA Ave. Subsidence: 5.2 ± 0.9 mm/yr ――> 3 yrs: 1.56 cm ――> 6.3 μGal change ~7 mm/yr wrt sl Dokka, et al. (2006) GRL Dokka, et al. (2006) GRL

  9. Current Status • Completed test phase of plan (flight altitude, speed, line spacing needed) in Alabama • Completed Airborne Surveys: • 2008: Alaska- Anchorage Louisiana- New Orleans • 2009: Puerto Rico and the Virgin Islands Louisiana- Lake Charles Texas coast- Austin Alaska- Fairbanks • Flight characteristics: 35000 ft (10 km) altitude, 280 knots • Preliminary gravity/GPS processing

  10. Anchorage Alaska- Anchorage • Survey flown out of Anchorage, AK over NOAA’s Hydropalooza Area in July, 2008 • 400km x 500km region coveredin ~100 flight hours

  11. Gulf of Mexico • First testing phase from Montgomery, AL in January 2008 • MS/LA began October 2008 • LA done February 2008 • TX started March 2008 • TX done May 2008

  12. Puerto Rico and the Virgin Islands • Flown in January in 100 flight hours • Completes our second test survey for the GRAV-D plan

  13. Alaska- Fairbanks Survey • Survey sponsored by NGA • Flown from Eielson AFB • Naval Research Lab C-12 King Air Aircraft • Flown at 12,500 ft at ~220 kts, 7.5 km line spacing • Nearly 120 flight hours • Incorporated U.S. Geologic Survey magnetometer

  14. Alaska- Fairbanks Survey

  15. GRAV-D Priorities • Highest Survey Priority: Alaska • High Priority:Great Lakes RegionEast Coast USWest Coast US • Ultimate Goal:Entire US and holdings by 2017 (~70% by 2014)

  16. GRAV-D and the Future • Airborne Surveys: • Planning to fly most/all of AK in FY10 • First Congressional funding likely in FY10 • Leverage funding through partnerships with other federal agencies, industrial groups, and universities • Developing processing tools for precise gravimetry • Comparisons to GRACE, EGM08, and surface data Slide 18

  17. GRAV-D and the Future Long-Term Monitoring: • 2009 Workshop to bring program into focus • All interested parties invited to attend • FY2010 will see launch of the monitoring program • Looking for collaboration opportunities http://www.ngs.noaa.gov/GRAV-D/2009Workshop/

  18. Thank you! NGS Mission Statement: "To define, maintain and provide access to the National Spatial Reference System to meet our nation's economic, social, and environmental needs."

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