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Geosounding principles 1. Resistivity sounding measurements, methods in geochemistry and geophysics, 14a
Geoexploration, Elsevier
Scientific
19 (1981) 155-164 Publishing Company,
155 Amsterdam
-
Printed
in The Netherlands
Book Reviews Geosounding
Principles, 1. Resistivity Sounding Measurements, Methods in Geochemistry and Geophysics, 14A. 0. Koefoed. Elsevier, Amsterdam, 1979, 272 pp., US $65.50, Df. 130.00.
Although the DC resistivity method itself is long-established, satisfactory practical methods of interpretation did not emerge until computers became widely available. Since that time, in the early 1960’s, practical numerical methods have been developed to compute the effects of horizontally-layered (1-D) models, as well as models in which resistivity varies in two and three dimensions. Inversion methods to these models have also become almost commonplace. Further desirable improvements in computational speed, stability, accuracy and convenience are continually appearing in the literature. It is a simple fact that very few of these developments can be found in one reference. Rather. they are spread through a variety of journals, unpublished reports and special papers, making it awkward for teaching and for learning. Koefoed attacks this situation by attempting to collect in one book the important results relating to the 1-D problem, in which he and his students have contributed so significantly. The result, part research monograph and part practical instruction manual, has been done thoroughly and accurately from start to end. Beginning with a short introductory chapter on field procedure and equipment, chapters 2 and 3 set out and solve the boundary value problem, and define the several kernels which are in use. Apparent resistivity is defined in chapter 4 andintegral expressions for it are derived for the common electrode arrays. It is also indicated here how the logarithmic transformation of lengths transforms the Fourier-Bessel integrals to convolution integrals. The introductory portion end with chapters 5 and 6. In these, various methods of determining the array-dependent convolution operators (“resistivity filters”) are set out and programs are given which calculate the apparent resistivities. These are followed by three chapters on interpretation: graphical, iterative, and “direct”, i.e. noniterative. There follows a chapter (11) on the effects of departures from the assumed model, another on related measurements, and a final chapter containing two field examples. Other uses of the convolution scheme are brought out at appropriate places in the discussion. These include the non-usual problem of converting apparent resistivities taken in one array to their equivalent inanother. The book goes beyond being strictly a research monograph in several respects. Derivations are generally given in a tutorial fashion. Many of the interpretation schemes are explained by application to both simplified and real data. The last chapter is virtually case-historical. One of the strong points of the book is the inclusion of many computer programs, for computing array convolution operators, apparent resistivities
156
from models and models from apparent resistivities. These are in BASIC, a (non-ANSI) Fortran, and for the TI-SR52 pocket calculator. I tried several and (after minor modification) they work. However, the SR52 is no longer sold and its code does not run on its successors. One can almost always suggest improvements and modifications to books, and this one is no exception. For example, it would be most helpful in following the practical examples if apparent resistivities and kernels were tabulated as well as plotted. One could then use them in the programs without having to digitize the curves. The programs could be better documented, and sample inputs and outputs given. Neither of these changes would significantly affect the size of the book. The new practitioner, particularly in a region like coastal Holland, will want a better guide to electromagnetic effects than has been provided. Research monographs also are in danger of being rapidly superseded. Recent Scandinavian work on Fast Hankel transforms has filled a large gap in the understanding of the spectra and nature of convolution operators, confirming and extending the work in Delft. Editorially, the book is remarkably free of typographical error (“cangaroo” comes as a bitter blow in this part of the world). On the whole the book is well written, although occasionally word usage or sentence construction can be awkward and distracting. For example “unsolved” rather than “undissolved” (p. 11) and “reverting” instead of “reversing” (p. 13). Overall, Koefoed has done a valuable service by carefully selecting and presenting the wealth of new material in a readable book of modest size. K. VOZOFF (Sydney, N.S.W.)
Geosounding Principles, 2. Time- Varying Geoelec tric Soundings. Methods in Geochemistry and Geophysics, 14B. H.P. Patra and K. Mallick. Elsevier, Amsterdam, 1980, 419 pp., US$ 87.75, Dfl. 180.00. In reviewing this excellent book by H.P. Patra and K. Mallick I can honestly say that I read every page of it in detail (except the list of references). One of the reasons is that I have seldom come across an account of the electromagnetic theory of geoelectric sounding that is so eminently readable. The authors write with a lively style and in spite of some terse mathematics the book reads almost like a novel. That is not to say that there are no faltering steps in the book. There are and I will return to these but let me first of all get over a few less flattering trivia. The book has its share of eccentric turns of English (“an alternating cable”, p. 84; “with the measurement of phase it is likely to detect thinner intermediate layers as compared to the amplitude measurements”, p. 137; “angle subtended by the line passing through the observation point and the vertical”,
Scientific
19 (1981) 155-164 Publishing Company,
155 Amsterdam
-
Printed
in The Netherlands
Book Reviews Geosounding
Principles, 1. Resistivity Sounding Measurements, Methods in Geochemistry and Geophysics, 14A. 0. Koefoed. Elsevier, Amsterdam, 1979, 272 pp., US $65.50, Df. 130.00.
Although the DC resistivity method itself is long-established, satisfactory practical methods of interpretation did not emerge until computers became widely available. Since that time, in the early 1960’s, practical numerical methods have been developed to compute the effects of horizontally-layered (1-D) models, as well as models in which resistivity varies in two and three dimensions. Inversion methods to these models have also become almost commonplace. Further desirable improvements in computational speed, stability, accuracy and convenience are continually appearing in the literature. It is a simple fact that very few of these developments can be found in one reference. Rather. they are spread through a variety of journals, unpublished reports and special papers, making it awkward for teaching and for learning. Koefoed attacks this situation by attempting to collect in one book the important results relating to the 1-D problem, in which he and his students have contributed so significantly. The result, part research monograph and part practical instruction manual, has been done thoroughly and accurately from start to end. Beginning with a short introductory chapter on field procedure and equipment, chapters 2 and 3 set out and solve the boundary value problem, and define the several kernels which are in use. Apparent resistivity is defined in chapter 4 andintegral expressions for it are derived for the common electrode arrays. It is also indicated here how the logarithmic transformation of lengths transforms the Fourier-Bessel integrals to convolution integrals. The introductory portion end with chapters 5 and 6. In these, various methods of determining the array-dependent convolution operators (“resistivity filters”) are set out and programs are given which calculate the apparent resistivities. These are followed by three chapters on interpretation: graphical, iterative, and “direct”, i.e. noniterative. There follows a chapter (11) on the effects of departures from the assumed model, another on related measurements, and a final chapter containing two field examples. Other uses of the convolution scheme are brought out at appropriate places in the discussion. These include the non-usual problem of converting apparent resistivities taken in one array to their equivalent inanother. The book goes beyond being strictly a research monograph in several respects. Derivations are generally given in a tutorial fashion. Many of the interpretation schemes are explained by application to both simplified and real data. The last chapter is virtually case-historical. One of the strong points of the book is the inclusion of many computer programs, for computing array convolution operators, apparent resistivities
156
from models and models from apparent resistivities. These are in BASIC, a (non-ANSI) Fortran, and for the TI-SR52 pocket calculator. I tried several and (after minor modification) they work. However, the SR52 is no longer sold and its code does not run on its successors. One can almost always suggest improvements and modifications to books, and this one is no exception. For example, it would be most helpful in following the practical examples if apparent resistivities and kernels were tabulated as well as plotted. One could then use them in the programs without having to digitize the curves. The programs could be better documented, and sample inputs and outputs given. Neither of these changes would significantly affect the size of the book. The new practitioner, particularly in a region like coastal Holland, will want a better guide to electromagnetic effects than has been provided. Research monographs also are in danger of being rapidly superseded. Recent Scandinavian work on Fast Hankel transforms has filled a large gap in the understanding of the spectra and nature of convolution operators, confirming and extending the work in Delft. Editorially, the book is remarkably free of typographical error (“cangaroo” comes as a bitter blow in this part of the world). On the whole the book is well written, although occasionally word usage or sentence construction can be awkward and distracting. For example “unsolved” rather than “undissolved” (p. 11) and “reverting” instead of “reversing” (p. 13). Overall, Koefoed has done a valuable service by carefully selecting and presenting the wealth of new material in a readable book of modest size. K. VOZOFF (Sydney, N.S.W.)
Geosounding Principles, 2. Time- Varying Geoelec tric Soundings. Methods in Geochemistry and Geophysics, 14B. H.P. Patra and K. Mallick. Elsevier, Amsterdam, 1980, 419 pp., US$ 87.75, Dfl. 180.00. In reviewing this excellent book by H.P. Patra and K. Mallick I can honestly say that I read every page of it in detail (except the list of references). One of the reasons is that I have seldom come across an account of the electromagnetic theory of geoelectric sounding that is so eminently readable. The authors write with a lively style and in spite of some terse mathematics the book reads almost like a novel. That is not to say that there are no faltering steps in the book. There are and I will return to these but let me first of all get over a few less flattering trivia. The book has its share of eccentric turns of English (“an alternating cable”, p. 84; “with the measurement of phase it is likely to detect thinner intermediate layers as compared to the amplitude measurements”, p. 137; “angle subtended by the line passing through the observation point and the vertical”,