[G02-6] Height systems

[G02-6-05] NGS' Gravity for the Redefinition of the American Vertical Datum Project Update and Developments

^○Vicki Childers, Monica Youngman, Theresa Damiani (NOAA/National Geodetic Survey, Silver Spring, MD, USA)

NOAA's National Geodetic Survey (NGS) defines latitude, longitude, and heights for the nation. NGS has recognized the need to update both our geometric and geopotential reference frames and plans to release updated frames in 2022. Our current vertical datum, the North American Vertical Datum of 1988 (NAVD 88), is a height system based upon geodetic leveling and realized at more than 500,000 monuments. NGS has chosen to replace this datum with one based upon a gravimetric geoid. The goal is to allow the user community to determine orthometric heights accurate to 2 cm through GNSS measurement plus a geoid height model. To create a geoid accurate to the needed 1 cm, the gravity field must be recovered at sufficient accuracy across the entire nation and its territories. NGS designed the Gravity for the Redefinition of the American Vertical Datum (GRAV-D) project to accomplish this purpose. GRAV-D involves a nationwide airborne gravity campaign designed to capture medium wavelength gravity data (20 – 500 km) to allow proper spectral blending with long-wavelength satellite gravity data from the GRACE and GOCE satellites with short-wavelength gravity information from terrestrial and shipborne measurements. From this blended gravity field we will create the gravimetric geoid that will be the basis of the new geopotential datum. This project has been underway for almost 9 years and is nearly 59% done as of February.

The GRAV-D project also includes long-term monitoring of geoid change over time so that the vertical datum will change as the Earth changes. NGS will monitor how gravity and hence the geoid changes over time and will update the vertical datum accordingly. We have named this effort the Geoid Monitoring Service (GeMS) and the research plan is currently under development.

In this presentation, we will present updates on the status of the GRAV-D project, discuss results of proof-of-concept experiments, and plans for the Geoid Monitoring Service.