THE SMOOTH SOUNDING GRAPH. A Manual for Field Work ... - BGR

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Contents 1 Preface 2 1. Basic rules 1.1. Ohm's Law 4 1.2. The homogeneous underground 4 1.3. The four-electrode arrangement 7 1.4. The layered underground 12 1.5. The fundamental principle for geoelectric sounding on a layered earth 15 1.6. Shifting of potential electrodes 22 2. Field activities 25 2.1. How to carry out a field measurement 26 2.2. Possible errors influencing the field measurements 37
Preface 2 This manual shall be a practical guide to surveyors, field operators, technical assistants, i.e. to all those who have to do the "dirty" work collecting field data under more or less bad conditions. Suffering under rough roads, hard climate and very often the lack of suffi- cient support by local officials a team "is thrown" into an area to be inves- tigated. Such a team has to provide its office or company with field data. In our case these field data are so-called resistivity sounding graphs. A graph is a sequence of data, which can be combined (by hand) to a more or less smooth curve. This procedure is not possible, if the data form a "cloud". Knowing that a cloud will not be accepted by the interpreter in the office the field group has to offer in any case rather smooth curves. This is their problem. Provided with a map where a grid of measuring points is plotted -often following the 1 inch-1 mile network- they start. Comparing their map (usually many years old) they find out, that an ac- curate measurement with the prescribed lay-out of say 500 m will end in a lake or in a new industrial plant or in a green paddy-field. The chance of shifting the measuring point is usually very low, because the grid may not be disturbed. Now it depends on the conscience of the chief surveyor in the field, to tell the truth, i.e. that a smooth curve at the prescribed point and also in its neighbourhood is impossible. His scientific opinion cannot allow him to "cook data" even when being sure, that the interpreter will never control him. Thinking on his own promotion the "field-man" is really in a bad situation. The authors know from experience collected in many countries all over the world about just this situation. In order to make the best of it from the technical point of view this manual was written hoping that it may be a real help. A short remark has to be added. Only real direct current is concerned here. There are equipments using alternating current with very low fre- quencies. Those equipments may get sufficiently good results using rela-
Page 1: THE SMOOTH SOUNDING GRAPH A Manual
Page 5 and 6: 1. Basic rules 4 The first chapter
Page 7 and 8: This current density is marked as j
Page 9 and 10: 8 Fig.2 Fig.3 Fig.4 Fig.5
Page 11 and 12: 10 1.3. The four-electrode arrangem
Page 13 and 14: 12 Fig.6 Fig.7 Fig.8
Page 15 and 16: 14 If we compare equations (10) and
Page 17 and 18: Case 2 (Fig. 10) 16 Now we observe
Page 19 and 20: 1.5. The fundamental principle for
Page 21 and 22: Case 3 (Fig.14) 20 The electrode di
Page 23 and 24: with just the same factor K. 22 Aft
Page 25 and 26: 24 Fig17 layers with different resi
Page 27 and 28: 26 Simulating this zooming by enlar
Page 29 and 30: 28 1.6. Shifting of potential elect
Page 31 and 32: 30 Fig.21 Fig.22 Fig23
Page 33 and 34: 32 2.1. How to carry out a field me
Page 35 and 36: L/2 a/2 1,5 6,28 2 11,8 2,5 18,9 34
Page 37 and 38: 36 Fig.27 Fig.28 Before we start th
Page 39 and 40: 38 fence, ditch) especially, if the
Page 41 and 42: 40 by experience. The measurement i
Page 43 and 44: 42 2.2. Possible errors influencing
Page 45 and 46: 2.2.4. Crossing a ditch (Fig.26/29)
Page 47 and 48: 46 accuracy is not so important the
Page 49 and 50: 2.2.8. Insulation and leakage curre
Page 51 and 52: 50 Fig.31. They are ascending with
Page 53 and 54:
52 If j' is negative, i.e. the dist
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THE SMOOTH SOUNDING GRAPH. A Manual for Field Work ... - BGR

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