The reduction of aliasing in gravity anomalies and geoid heights using digital terrain data

Observations of gravity can be aliased by virtue of the logistics involved in collecting these data in the field. For instance, gravity measurements a re often made in more accessible lowland areas where there are roads and tr acks, thus omitting areas of higher relief in between. The gravimetric dete rmination of the geoid requires mean terrain-corrected free-air anomalies; however, anomalies based only on the observations in lowland regions are no t necessarily representative of the true mean value over the topography. A five-stage approach is taken that uses a digital elevation model, which pro vides a more accurate representation of the topography than the gravity obs ervation elevations, to reduce the unrepresentative sampling in the gravity observations. When using this approach with the Australian digital elevati on model, the terrain-corrected free-air anomalies generated from the Austr alian gravity data base change by between 77.075 and -84.335 mgal (-0.193 m gal mean and 2.687 mgal standard deviation). Subsequent gravimetric geoid c omputations are used to illustrate the effect of aliasing in the Australian gravity data upon the geoid. The difference between 'aliased' and 'non-ali ased' gravimetric geoid solutions varies by between 0.732 and -1.816 m (-0. 058 m mean and 0.122 m standard deviation). Based on these conceptual argum ents and numerical results, it is recommended that supplementary digital el evation information be included during the estimation of mean gravity anoma lies prior to the computation of a gravimetric geoid model.