A new methodology to process airborne gravimetry data: advances and problems

In the framework of the development of a new methodology for the processing of airborne gravity data, we discuss the problem of edge effects and the treatment of long-wavelength errors in the local geoid solution. The new methodology combines several pre-processing steps, such as filtering and cross-over adjustment, with the parameter estimation. The base functions used in the analytical representation of the disturbing potential are the fundamental solutions of Laplace’s equation in Cartesian coordinates. This implicitly assumes periodicity in the gravity data, which does not hold in practice. The limitation to the local area introduces highly oscillating distortions in the adjusted gravity disturbances, which are mainly located along the boundary of the area. These distortions cause long-wavelength errors in the geoid over the whole area. We investigate five approaches to reduce these effects, using a simulated data set. Among these methods, least-squares prediction used to extend the data set gives the best gravity field solution in terms of gravity disturbances. However, the solution still suffers from long-wavelength geoid errors, which partially reflects the non-uniqueness of local geoid determination from airborne gravity data. Therefore, two alternative methods are investigated, which aim to solve this problem. We show that it is possible to slightly reduce the long-wavelength errors, in particular at the center of the area.