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.

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Recent News:

NGS-Norfolk Surveyor Assists with GRAV-D Measurements

Kevin Jordan, NGS’ Observations and Analysis Division, will travel from NGS Field Operations Branch in Norfolk, Virginia, to the Patuxent River Naval Air Station in Lexington Park, Maryland, to perform a component spatial relationship survey on the Gravity for the Redefinition of the American Vertical Datum (GRAV-D) aircraft. [more...]

The GRAV-D Survey over Lake Superior Underway

NGS had contracted with Fugro to provide airborne services and operators for a two-month long Gravity for the Redefinition of the American Vertical Datum (GRAV-D) survey effort over Lake Superior. The recently-acquired TAGS gravity meter was installed in this aircraft for the survey. [more...]

NGS continues work with University of Arizona and USGS to Study Ground Water Recharge near Tucson

In late June, NOAA personnel will return to Tucson, Arizona, with the FG5 absolute gravimeter to perform part two of three joint gravity measurements with the University of Arizona-Hydrology Department, the U.S. Geological Survey's (USGS) Water Resources Division, and others. [more...]

NGS’ Vicki Childers Presents at NASA Goddard Space Flight Center

On April 11, Dr. Vicki Childers presented an invited talk at NASA’s Goddard Space Flight Center’s “Solar System Exploration Seminar.” Vicki discussed advancements in airborne gravity science achieved by NGS’ Gravity for the Redefinition of the American Vertical Datum (GRAV-D) Project since its inception four years ago. [more...]

GRAV-D Completes Release of Gulf Coast Airborne Gravity Data for Public Use

Airborne gravity data covering most of the U.S. Gulf Coast from the Mexico border to Alabama is now available on NGS’ Gravity for the Redefinition of the American Vertical Datum (GRAV-D) website. This is a milestone for the program which is designed to produce high-accuracy airborne gravity data to contribute to a new vertical reference frame accurate at the 2 cm level (where possible). [more...]

U.S. and Canada Agree to Joint North American Height Datum

NOAA’s National Geodetic Survey (NGS) and Natural Resources Canada (NRC) have agreed, in writing, to developing a common vertical reference system in North America and what the definition of “zero height” will be for the new system. [more...]