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

GRAV-D is a proposal by the National Geodetic Survey to re-define the vertical datum of the US by 2021.

The gravity-based vertical datum resulting from this project will be accurate at the 2 cm level for much of the country. The proposal is official policy for NGS and is included in the NGS 10 year plan. The project is currently underway and actively collecting gravity data across the United States and its holdings. Why is the Vertical Datum important?

The GRAV-D project consists of three major campaigns:

1. A high-resolution "snapshot" of gravity in the US:

This is a predominantly airborne campaign, to be accomplished around 2017 and at a cost of ~39 Million dollars. The highest priority targets are: Alaska, Puerto Rico and the Virgin Islands, the Gulf Coast, the Great Lakes, and Hawaii (some portions of which have already been completed). The coastline of the continental US and the American island holdings are also of high priority.

2. A low-resolution "movie" of gravity changes:

This is primarily a terrestrial campaign and will mostly encompass episodic re-visits of absolute gravity sites, attempting to monitor geographically dependent changes to gravity over time. This will allow time dependent geoid modeling and thus time dependent orthometric height monitoring through GNSS technology.

3. Regional partnership surveys:

NGS seeks to collaborate with local (governmental, commercial, and academic) partners throughout the GRAV-D project. Partners that are willing to support airborne or terrestrial surveys or to monitor local variations in the gravity field are a critical component of GRAV-D. Please contact us if your organization is interested in collaboration.

---

Recent News:

NGS’ Dan Winester Presents at EarthScope Conference

NGS’ Dan Winester will be attending the EarthScope Conference in Austin, Texas from May 17-20. EarthScope hosts the Plate Boundary Observatory (PBO), a large contributor to the Continuously Operating Reference Stations (CORS) network.[ more... ]

NGS Presents Widely Attended Webinar on GRAV-D Project

National Geodetic Survey’s Dr. Theresa Diehl presented a free webinar on May 9 with about 100 attendees from across the country and from various organizations, including federal, state, university, and surveying/environmental corporations. In the webinar titled An Update on the Gravity for the Redefinition of the American Datum (GRAV-D) Project, Diehl discussed the current vertical datum used on federal maps and why NGS’ GRAV-D Project was instated to create a new, 2 cm-accurate datum.[ more... ]

Community Surveyors to Experience Significance of NOAA GRAV-D Airborne Operation

On February 5, the National Geodetic Survey (NGS) California State Geodetic Advisor, Marti Ikehara, brought 22 surveyors from the local community to view NGS Gravity for the Redefinition of the American Vertical Datum (GRAV-D)airborne operation at McClellan Field in Sacramento, CA.[ more... ]

NOAA National Geodetic Survey Acquires New Absolute Gravity Meter for Increased Effectiveness and Efficiency of Gravity Readings

NOAA National Geodetic Survey (NGS) has acquired a new A10 absolute gravity meter for terrestrial survey work that will be used to establish gravity ties for airborne gravity surveys.[more...]

NOAA National Geodetic Survey Adds a Second Pilot to its GRAV-D Sacramento Airborne Survey to Boost Survey Coverage

On February 1, a second pilot was added to NOAA National Geodetic Survey Gravity for the Redefinition of the American Vertical Datum (GRAV-D) operation in the Sacramento, California survey.[more...]

NOAA to Highlight GRAV-D at American Geophysical Union Annual Fall Meeting

NOAA National Geodetic Survey (NGS) will present at the American Geophysical Union (AGU) Annual Fall Meeting in San Francisco, CA from December 13 to 17. NGS contributions at the AGU conference include analysis and information regarding NGS gravity collection activities and their applications. NGS will also provide sessions on its Gravity for the Redefinition of the American Vertical Datum (GRAV-D) Project initiative and related work. For more information, contact Vicki Childers[more...]

GRAV-D Alaska Survey Operations to Conclude for the Season in Anchorage,AK

NGS Gravity for the Redefinition of the American Vertical Datum (GRAV-D) airborne team transitioned to Anchorage, AK from Fairbanks for its final week (ending November 15) for the 2010 calendar year.[more...]

NGS Sandra Preaux is Awarded NOAA Team Member of the Month

Congratulations to Sandy Preaux upon her selection as NOAA Team Member of the Month! Sandy is an airborne gravity scientist with NGS Gravity for the Redefinition of the American Vertical Datum (GRAV-D) Project, and she is being honored for her many contributions to the team. [more...]

Vicki Childers to Present at National Digital Orthoimagery Program

Vicki Childers, NGS Gravity for the Redefinition of the American Vertical Datum (GRAV-D) Project Manager, has been requested by the National Digital Ortho Photo (NDOP) group to provide a 20-minute presentation on GRAV-D at their upcoming meeting in Pascagoula, MS on November 17.[more...]

NOAA Hosts North American Comparison of Absolute Gravimeters

NOAAs National Geodetic Survey (NGS) will host the North American Comparison of Absolute Gravimeters (NACAG-2010) from October 18 to 22 at NGS Table Mountain Geophysical Observatory (TMGO) in Longmont, CO. Other U.S. federal agencies, as well as other government agencies from Canada, will participate, with tentative plans including nine absolute gravimeters for the comparison.[more...]