The presence of multiaquifer or multilayer wells changes the nature of the equations which must be solved in a three‐dimensional ground‐water flow simulation and, in effect, alters the stencil of computation. A method has been devised which takes this change into consideration by allowing simulation of the hydraulic effects of a multiaquifer well on the aquifer system. It also allows for calculation of the water level and individual aquifer discharges in such a well. The method is valid for the case of a single well located at the center of a square node block. Where more than one well per node is involved, the effects of the stencil alteration still must be considered, although difficulties arise in estimating and justifying the parameters to be utilized.
Cubic spline interpolation is a mathematical procedure which is an analog of the draftsman's plastic spline. The advantage of this interpolation procedure over the more commonly used methods such as Lagrange lies in its ability to not only fit each given data value exactly but to maintain continuity of the first and second derivatives. The relative accuracy of the cubic spline interpolation procedure for generating gridded data values and estimates of mean gravity anomalies from track-type geophysical surveys is shown to be excellent when applied to properly designed surveys. Techniques for interpreting the two-dimensional Fourier transform in terms of track spacing, track orientation, and down -track sampling rate are presented todemonstratetheeffect of these parameters on interpolation accuracy. A procedure for utilizing closed form integration of the bicubic spline surface to produce mean gravity anomalies is shown to yield accuracies comparable to the method of averaging cubic spline grid values.
Data for model row 19, columns 3 through 19 (lines 409 through 424) are missing and are the same as model row 2, columns 3 through 19 (lines 103 through 118). Data for all of model row 20 (lines 425 through 442) are missing, and are the same as model rowl (lines 83 through 100). The correct entries for missing lines 409 through 442 are listed below. (2). APPENDIX 4, Page 48-In "ARRAY SHOWING STATUS OF TOPMOST CELLS": Entries for model column 6 of rows 5, 6, and 15 should be 66 not 77.
The theoretical basis for applying the upward‐continuation integral, [Formula: see text]z⩽0, (1) to total magnetic intensity data T(α, β) measured on the plane z=0 has been recently reviewed by Henderson (1970). To perform upward continuation in the spatial domain, weights or coefficients obtained by numerical evaluation of equation (1) (Peters, 1949; Henderson, 1960; Fuller, 1967) may be convolved with the total intensity anomaly T(α, β) to produce T(x, y, z) at heights z<0 (for z positive downward). The accuracy of upward continuation is, therefore, dependent on the validity of the numerical coefficients and of the assumptions required to show that T(α, β) satisfies the conditions of the Dirichlet problem for a plane. These assumptions are that the quantity sensed by a total‐intensity magnetometer is in the direction of the earth’s normal field and that this direction is invariant over the area of interest.
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