Abstract

It is well and good to bring airborne gravity to the attention of practicing geophysicists, but at the very least the presentation must be correct. The logical test of accuracy only can be found in the comparison of ground and airborne positive, caprock anomalies. Other evidence is illogical, i.e., measurements of how well the airborne system is repeating itself. The caprock example in Figure 8 best marks the nonauthenticity. The ground anomaly at High Island appears to be 4 mgal, estimating the position of the salt minimum to which the positive must be referred. (The actual value of the positive could have been provided in the text.) The airborne positive at 1000 ft asl, approximately 800 ft above ground level and 1100 ft above caprock (estimated from Figure 8, again not given), appears to be 1 mgal. Well, instead of modeling the ground anomaly, then computing the model's anomaly at 1000 ft (an excellent method of continuation which may use a synthetic model if no subsurface facts were available, which doesn't need gridded data, only modeling the observed points), the author resorts to a demonstrably erroneous method of filtered continuations, further confused by the absence of vertical and horizontal scales in Figure 9.

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