1. 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

2. 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

3. NGS-held point surface gravity measurements 2,155,662 surface gravity measurements scattered throughout North America mixture of NGS & NGA-proprietary data

5. 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

6. 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)

7. GRAVITY-LIDAR COLLECTION MISSION

11. 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

12. 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.