-several spike values are observed and represent points that are similarly suspect to those that are already removed -some of these points were subsequently removed (they are counted in the 123 total removed points) but the overall model did not change by their removal

Definition (1) is preferred.

The EGM96 surface was enhanced using local gravity and terrain data to create a regional geoid model (USGG2003). The difference between the enhanced EGM96 surface and that implied by the 14185 GPSBM’s serving as control data are significant. Not all problems are related to a bias difference, significant trends occur along the coasts. The question is, which is more correct? Another line of evidence would be need to ascertain this – namely a comparison with the actual sea surface and a modeled mean dynamic topography: GEOID + MDT + MSSH Hence comparison of the gravimetric geoid and MDT models at coastal stations (TBM’s) might resolve the datum question in an absolute sense. This seems to offer some hope of deriving a seamless and consistent set of gravity across the region. These gravimetric geoid values may be directly compared to the NAVD 88 datum at tidal bench marks to estimate the magnitude of error in NAVD 88 – ASSUMING the derived gravimetric geoid agrees well with the MDT and tide models as well as the observed lidar sea surface heights.

A geoid model should predict the surface between two known points (blue) and the unknown point (green) However, the absolute accuracy of NAVD 88 datum is unknown WRT to the “true” geoid and MSL Need to study the relationship between gravimetric geoid, MSL, and NAVD 88 at TBM‘s

Numerous TBM’s exist where the NAVD 88 value and ocean surface (MDT+geoid) are both known. These sites could suffice, providing that suitable gravimetric geoid and MDT models are generated.

Models for the Gulf of Mexico already exist, however, data gaps in the littoral regions raise questions about the continuity of the data at the shoreline. Additionally, possible biases may exist between offshore and terrestrial data. What is desired is a seamless set of gravity values from the offshore to the onshore to best evaluate the geoid at the shoreline.

Gravity data at 28,000 feet collected during GLS05. Block-meaned at 1/8 degree, then minimum curvature spline.

Difference between upward continued surface gravity (using GRIDFFT from GMT) and aerogravity grid (min. curvature). In general, there is good agreement. Many of the remaining features are likely artifacts from the rough data and require further processing.