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 2022.
The gravity-based vertical datum resulting from this project will be accurate at the 2 cm level where possible 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 two major campaigns:
1. A high-resolution "snapshot" of gravity in the US:
This is a predominantly airborne campaign, to be accomplished around 2022 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.
Regional partnership surveys:
NGS also 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.
