Refinement of gravimetric geoid using GPS and leveling data

A gravimetric geoid model does not allow the accurate transformation of Glo bal Positioning System (GPS) ellipsoidal heights to Australian Height Datum (AHD) heights in the Perth region of Western Australia. This is predominan tly due to the effect of the geological structures associated with the Darl ing Fault, the availability and quality of data and the possibility of dist ortions in the AHD. Therefore a combined solution is sought, where 99 coloc ated GPS and AHD heights are used to adjust the gravimetric geoid such that it provides a model of the separation between the AHD and the GRS80 refere nce ellipsoid. This data combination was investigated using least-squares c ollocation and continuous curvature splines in tension. The least-squares c ollocation technique was found to give an improved model of the AHD-GRS80 s eparation, as shown by a standard deviation of fit of the combined model to the control data of +/- mm. In comparison, the gravimetric geoid gives a s tandard deviation of fit to the control data of +/- 128 mm.