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

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3 tively short lay-outs. Investigating the deeper underground the skin-effect will come in and difficulties will arise which are not discussed within this manual. Hannover, November 1976 H. FLATHE W. LEIBOLD
1. Basic rules 4 The first chapter deals with the fundamentals of direct current resistivity measurements. The attempt was made to give an elementary introduction into what really happens within the earth during a measurement. The physical process should be understood by the reader. Each physical parameter will be checked with respect to its influence on the measured data. This will be done by reducing mathematical formulae to a minimum. A well-trained mathematician will sometimes have a bad feeling seeing the rigorous way of using mathematical "tools". But this manual is written for a field crew working with modern equipments on the earth’s surface. Going on step by step in recording data they should follow up in mind the subsurface process, i.e. they should know what they are really doing. One remark should be added: In the theoretical part of this chapter only one very simple integral appears. The authors would be very glad if read- ers could make any proposal to get rid of this integral in explaining the necessary background of direct current resistivity sounding. 1.1. Ohm's Law Geo-electrical measurements are carried out on the earth's surface. The air space is assumed as an insulator and the earth's surface as a plane. The underground is an electrical conductor. A direct current is running from the surface through this conductive infinite half-space, limited above by the plane earth's surface. Which laws are valid for this current flow through the underground? Regarding electrical currents we generally are accustomed to think of a wire. A wire has a certain resistance which can be calculated from Ohm's law. We regard (see Fig.1) a wire of the length a, measured in meters [m] with a cross-section q, measured in [m 2 ]. Ohm's law then can be written as U I a = R = ρ (1) q
Page 1 and 2: THE SMOOTH SOUNDING GRAPH A Manual
Page 3: Preface 2 This manual shall be a pr
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

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

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