Status and Plans of the National Geodetic Survey’s Gravity Database Update

Daniel R. Roman and Yan Ming Wang

October 13-14, 2005 Austin, Texas

DISCUSSION OUTLINE

• NGS-held point surface gravity measurements

• Problems in the current gravity database

• The first effort to fill in data gaps near shore

• Future Plans• Invitations

NGS-held point surface gravity measurements

• 2,155,662 surface gravity measurements scattered throughout North America

• mixture of NGS & NGA-proprietary data

Problems in the current gravity database:

• Tidal systems differ between NGS (tide-free) and NIMA-proprietary (mean tide) data

• Data reference NAD27 & NGVD29 but can be converted to NAD83 & NAVD88

• Data collected for a long time period (dating back more than 80 years), may contain local or regional biases

• Effect of subsidence and the Earth’s crustal movement on gravity has become considerable

• Data gaps in near shore and difficulty-to-access areas

The first effort to fill in data gaps near shore:

• NGS/NRL/GSFC joint airborne gravity and LIDAR mission in Golf of Mexico region

• Data were collected in May/June 2005• The misson’s goals are:

- To fill in data gaps near shore- Establish links between off-shore mean sea surface and the North America Vertical Datum 88 (NAVD88)

GRAVITY-LIDAR COLLECTION MISSION

Future Plans:

• The next study area will flow from the Florida panhandle through Louisiana into Texas along the Gulf coast

• Airborne missions over coastal and complete US continental are proposed

• A complete coastal and inland airborne survey is proposed

• Missions will be at 20 km cross track spacing and at 8.5 km altitude

Invitations:

• We are seeking corporations between government agencies, such as NGA, NRL, NASS and USGS.

• Research institutes and universities are welcome.• Private industry (oil companies and mapping companies) are

invited to participant.