The Airborne Gravity Off-Level Correction Revisited Using NGS GRAV-D Data

As part of the Gravity for the Redefinition of the American Vertical Datum (GRAV-D) project, the National Geodetic Survey (NGS) is collecting airborne gravity data at a 10km spacing throughout the entire United States and its territories. Before data from adjacent flight lines are combined, an Eotvos correction (accounting for east-west velocities that couple into the gravity vector) and an off-level correction (accounting for a misalignment of the sensor axis with the gravity vector) need to be applied. This second effect is notoriously difficult to calculate in a moving and tilting aircraft. We present a comparison of two techniques developed by Peters & Brozena (1995) and Oleson (2002), applied on data from two different instruments and over a large range of flight conditions, using cross-over statistics as a metric. Preliminary comparisons indicate an improvement in correction and bias using the second method.