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 2017.

The gravity-based vertical datum resulting from this project will be accurate at the 1-2 cm level. 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.

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Recent News:

NOAA Collaborates With Other Federal Agencies on Airborne Gravity Survey in Western Alaska

August 2009- NOAA's National Geodetic Survey completed a Gravity for the Redefinition of the American Vertical Datum (GRAV-D) airborne survey in western interior Alaska on August 11th, with portions of western interior Alaska area flown.  This survey represents a landmark in the GRAV-D initiative, due to the collaboration with two other federal agencies.the Naval Research Lab (NRL) and the US Geological Survey (USGS). [more...]

Socio-Economic Benefits of GRAV-D estimated at $522 Million

June 2009- Leveson Consulting has evaluated the benefits to the US economy provided by NOAA-NGS' National Spatial Reference System, including CORS and GRAV-D. The report was presented at a briefing on Capitol Hill and is available online. The expected value of GRAV-D (half of which is from projected improvements in flood plain mapping) is $522 Million dollars annually. [more...]

Western Gulf Coast Survey Completed

May 2009- A massive GRAV-D effort to survey the Gulf coast from the Texas/Mexico border to the Alabama/Mississippi border, partially funded by the Army Corps of Engineers, was completed in mid-May 2009. The multi-part survey was started in October 2008 in response to the need of the Army Corps for future storm preparedness and, thus, a better vertical datum in the Gulf. [more...]

University of Texas at Austin Students Experience GRAV-D Operations

March 2009- The GRAV-D team hosted a group of undergraduate students from a geophysics class at the University of Texas at Austin on the 10th. The students learned about gravity fundamentals and were able to examine the actual GRAV-D instrumentation, while the team and plane were in Austin for the western Gulf of Mexico survey. [more...]

GRAV-D Completes Survey of Puerto Rico and the Virgin Islands

January 2009- Flying ~100 hours over the course of nearly 4 weeks, the GRAV-D team has completed both a high-altitude survey (measuring 400 km x 500 km) at 35,000 ft over Puerto Rico and the Virgin Islands, as well a small low-altitude survey nominally at 5,000 ft over the Virgin Islands. The survey was a huge success. [more...]

Two New Hires for GRAV-D

January 2009- The program acquired two new team members this month. Dr. Theresa Diehl joined the Silver Spring, MD office as a specialist in airborne gravity data collection and processing. David Schmerge joined the Table Mountain Gravity Observatory in Boulder, CO with a background in absolute gravimeter operations. [more...]