Australian Synthetic Earth Gravity Field Model (aussegm) ¡V a Rgional Earth Gravity Field Model

Australian Synthetic Earth Gravity Model (AusSEGM) is a regional source-effects model SEGM over the area of Australia. It uses a global geopotential model (GGM, here EGM96) as effects model to supply the long wavelength component, and forward modelling results of a regional simulated mass distribution of the topography with a 3-arc-sec by 3-arc-sec resolution as source model to supply the finer resolution. Both the GGM as well as the simulated local/regional mass distribution are assumed to be perfectly known and error-free. AusSEGM provides exact and self-consistent high-resolution simulated gravity-field functional (such as geoid heights and gravity observations). Thus AusSEGM is ideal for validating theories, techniques and computer software for regional geoid determination. This paper describes the construction of AusSEGM as well as first results. The coarse structure of the field was taken from EGM96 (Nmax = 360), whilst the finer structure was computed from a 3-arc-sec by 3-arc-sec simulated digital elevation model (DEM) over Australia. This first version of AusSEGM uses a constant density distribution of ƒâ = 2670 kg/m3 for the topographic masses. The global 30-arc-sec by 30-arc-sec DEM GLOBE is the basis for the high resolution DEM over Australia, where the higher resolution has been obtained by adding a fractal surface. From these data, the effect on gravity field (potential and gravitational attraction) has been determined using Newton¡¦s integration. Furthermore, these effects have been separated into a long- and short wavelength part using a spherical harmonic expansion (up to degree Nmax). The high-pass filtered short-wavelength constituent has then been added to the long-wavelength information of EGM96. AusSEGM provides gravity values at the Earth¡¦s surface and geoid heights at regular geographic grid nodes (1-arc-min by 1-arc-min) as well as arbitrary points with a similar distribution as measured gravity points. The precision of the synthetic gravity and geoid data (after a first iteration) is estimated to be better than 30 ƒYGal and 3 mm, respectively.