I read the above paper by Guptasarma (1983) with great interest since it concerns the work done jointly by a group that includes me (Apparao et al., 1980). While I agree with some of his conclusions, I disagree with the others.

The article reports an interesting result that, in physical modeling for resistivity and IP, an excitation current frequency of at least twenty times the maximum characteristic frequency (fc)max must be used along the length of the profile, when one employs either a solid metallic conductor as a target or electronic conducting material in the target. He also reports that the value of fc is as low as 4.5 Hz with some models. For many others (not measured by Guptasarma), (fc max) may turn out to be much less than 1 Hz. He hastened to conclude that all the laboratory measurements carried out at 50 or 60 Hz (referring to our papers) are likely to be grossly erroneous and should be viewed with “suspicion.” That his conclusion is incorrect can be seen from the following five-point discussion.

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