1	Evaluation of the NAVD 88 Using Aerogravity and Lidar Data in the Gulf of Mexico Authors Daniel R. Roman (NGS), John Brozena (NRL), Scott Luthcke (GSFC), Yan Ming Wang (NGS), Vicki Childers (NRL), J. Bryan Blair (GSFC) Support Staff NRL: Sandy Martinka, James Jarvis, Robert Liang, GSFC: David Rabine, Hannes Greim, Michelle Horton
2	DISCUSSION OUTLINE Overview Collection Mission The NAVD 88 Datum Future Plans Conclusions
3	OVERVIEW Existing vertical datum for U.S., NAVD 88, has meter-level bias and trend problems Altimeter profiles across Great Lakes Comparisons to GRACE-based EGM’s Use GRACE-based EGM’s enhanced by local gravity for datum definition Need to ensure the gravity data are consistent and seamless From offshore to onshore (shipborne vs. terrestrial groups) Fill in gapped regions and edge regions Gravimetric Geoid + MDT = Observed Mean Sea Surface Need open-ocean lidar observations for MDT Can validate this approach at coastal stations (TBM’s) Benefits: more accurate coastal heights, improved emergency and coastal management, validation of satellite missions (on a larger scale)
4
5
6
7	GRAVITY-LIDAR COLLECTION MISSION
8
9
10
11
12	Profile comparisons of the track 3 of flight 13
13	Future Efforts Aerogravity must be downward continued or otherwise combined with existing surface gravity data Lidar data must be finalized Mean Dynamic Topography model developed The models need to be compared for mutual validation: Geoid + MDT + Tide = lidar-obs instantaneous sea surface The next study area will flow from the Florida panhandle through Louisiana into Texas along the Gulf coast MDT issues aren’t as severe there, but terrestrial subsidence issues are very significant in Louisiana Proof of concept for a larger production in FY08 and beyond
14	Conclusions Significant errors exist within the NAVD 88 Similar magnitude errors could exist within EGM96 or other EGM’s Future EGM’s will directly impact the gravimetric geoid solutions at the long to intermediate wavelengths Seamless gravity data is needed from deep ocean onto shore and off the opposite national coast(s) to resolve shorter wavelengths Resulting gravimetric models can be studied in the context of MDT models to determine the best fitting littoral geoid The implication then would be that these models would also be suitable in the interior Such geoid models will better resolve orthometric heights and provide an improved relationship between oceanographic and terrestrial applications