DOWNWARD CONTINUATION OF AIRBORNE GRAVITY DATA USING HIGH-RESOLUTION GLOBAL GEOPOTENTIAL MODELS

Airborne gravimetry has proven to be a feasible method for gravity data collection over large areas. The survey results are used for a number of applications, such as geoid modelling, various geophysical studies and exploration of the natural resources. Obviously, the downward continuation is an important part of the airborne data processing. For instance, to satisfy the boundary condition (e.g. for the geoid modelling), the gravity data need to be downward continued from the flight altitude to the geoid level. This study uses a novel high resolution global geopotential model EGM08, which contains fully-normalized, unitless spherical harmonic coefficients, complete to degree and order 2159 (correspnding to the 5 arc-minutes spatial resolution) for downward continuation of airborne gravity data. A low-elevation (in average 500 ft) airborne gravity dataset over the Baltic Sea has been selected for the numerical assessment of the proposed downward continuation method. The EGM08 based downward continuation effect on the airborne gravity anomalies ranges from -0.76 to +0.68 mGal, with a mean of 0.024 mGal. The results are correlated with the flight altitude and the magnitude of anomalies. In particular, the downward continuation enhances the high-frequency component of gravity quantities in an increasing manner.