Knowledge Bank

In Section A, several methods for interpolation and extrapolation of gravity are described, such as geometrical interpolation, zero anomaly, representation, and least squares prediction. General formulas for the accuracy of any prediction method are deduced in Section B. Least squares prediction, which is the most accurate one, permits a purely numerical processing of gravity anomalies and seems to be excellently suited for electronic computers. The accuracy of the usual prediction methods is shown generally and by means of numerical examples and the influence of the configuration of gravity stations is studied. Section C deals with the prediction of mean anomalies. The important correlation of free-air anomalies with elevation is the subject of Section D. Least squares prediction is extended to this case, giving matrix formulas which can be used for machine computations. The validity of the usual method of Bouguer anomalies is investigated, including the error committed by using a wrong Bouguer gradient. An appendix deals with the error covariance function.