Continuous tracking of geodetic satellites using the Satellite Laser Ranging technique has provided unprecedented opportunity in
long- to medium-wavelength gravity field modelling. Numerous gravity field models have been derived from such observations and
have been made freely available to the science community for research purpose. The accuracy of most of the latest gravity field
models in terms of precise orbit determination is currently at cm level. Improvement in the Earth gravity field modelling is
anticipated as quantitative and qualitative data (in particular from low earth orbit satellites) become available in the future. Such
expectations require that the accuracy and precision of existing gravity field models be assessed. The validation of gravity field
models in terms of satellite orbit determination is often based on the difference between the observed and computed range.
The resulting range residuals are considered an important index when determining the accuracy of the gravity models and hence
the satellite orbits. In this contribution we investigate the general improvement in gravity field modelling over a period of 15 years.
The orbit accuracy of twelve gravity field models (both satellite-only and combined models) were assessed by analysing seven
months of data from LAGEOS 1 and 2 using HartRAO analysis software. Results show that the gravity field models developed over
the years have improved by at least a factor of 2 since 1990, considering improvement in O-C residuals.