Determining ġ and N and the Impact on the New Vertical Datum for North America

Daniel R. Roman, Ph.D.

2009 Workshop on Monitoring North American Geoid Change21-23 OCT 2009 Boulder, CO

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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

• 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

• 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

Static Snapshot: Airborne

• Provides intermediate wavelength gravity data• Reconciles terrestrial datasets• Fills in spatial gaps in the littoral region

Ship gravitytracks

Terrestrial gravity points

New Orleans

20-100 km gravity gaps along coast

Results: 2006 Joint NGS and NRL Airborne Survey

Difference with upward-continued gravity field

Resulting changes in geoid from new gravity data

Monitoring Change: Terrestrial• Uplift: tectonic, GIA• Subsidence: sediment compaction, tectonic,

water/oil pumping, GIA

Dokka, et al. (2006) GRL

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

Collaboration

• Other U.S. Agencies: Provide a common national model– NGA– USGS– USACE– FEMA– To better tie work of the whole of government

• Other Countries: Provide a common regional model– Canada– Mexico– Caribbean nations– Geoid is long wavelength– Transparency across borders with a seamless model

Collaboration

• International Organizations– International Association of Geodesy

• North American Geoid: – IAG CP 2.2 – Chair: Roman– Canada and Mexico are members

• Theoretical Improvements: – IAG IC-SG8 – Chair: Wang– Membership from around the world

• Ties with other IAG work groups– F.I.G

• Working to define how new vertical datum will be implemented and accessed

Scope of a North American Geoid/Vertical Datum

• Google Earth image showing Hawaii to Alaska to PR/VI

The NGS 10 year plan (2008-2018)

http://www.ngs.noaa.gov/INFO/NGS10yearplan.pdf

The GRAV-D Project Plan

http://www.ngs.noaa.gov/GRAV-D/pubs/GRAV-D_v2007_12_19.pdf

Socio-Economic Benefits of CORS and GRAV-D

http://www.ngs.noaa.gov/PUBS_LIB/Socio-EconomicBenefitsofCORSandGRAV-D.pdf

Additional Information

• NGS Contacts:– Dan Roman (PI), Dan.Roman@noaa.gov– Vicki Childers (PM), Vicki.Childers@noaa.gov– Dru Smith (Chief Geodesist), Dru.Smith@noaa.gov

• Always begin with your state advisor:– http://www.ngs.noaa.gov/ADVISORS/AdvisorsIndex.shtml

• NGS Information Center– Phone: (301) 713-3242– E-mail: ngs.infocenter@noaa.gov

• GRAV-D Website– http://www.ngs.noaa.gov/grav-d

Additional Information