Knowledge Bank

This report reviews the various methods for the description of the Earth's gravity field from direct and/or indirect observations. Geopotential models produced by various organizations and in use during the past 15 years are discussed in detail. Recent and future programs for the improvement of global gravity fields are reviewed and the expected improvements from new observation and data processing techniques are estimated. The regional and local gravity field is also reviewed. The various data types and their spectral properties, the sensitivities of the different gravimetric quantities to data types are discussed. The techniques for the estimation of gravimetric quantities and the achievable accuracies are presented (e.g. integral formulae, collocation). The results of recent works in this area by prominent authors are reviewed. The prediction of gravity outside the earth from surface data is discussed in two forms: a) prediction of gravity disturbance at high altitudes and b) upward continuation of gravity anomalies, The achievable improvements of the high frequency field by airborne gradiometry is summarized utilizing recent investigations. In the section of "Summary and Recommendations" the expected short- and long-term improvements are summarized and some recommendations are made for data processing and observation method.