Transformation of Dipole Resistivity Sounding Measurements Over Layered Earth by Linear Digital Filtering *

In this paper a technique for computing type curves for the two-electrode resistivity soundings is presented. It is shown that the apparent resistivity due to the system can be represented by a convolution integral. Thus, it is possible to apply the principle of digital linear filtering and compute the desired type-curves. The filter function required for the purpose is found to be identical with that used to compute the EM sounding curves for the two coplanar horizontal loop system.It is further shown that from the two-electrode apparent-resistivity expression one can easily derive the apparent resistivities for other configurations. A comparison of depths of investigation for various systems reveals that the two-electrode system has greater depth of investigation than other conventional systems. This is also supported by the field example presented in the end, which illustrates the relative performance of the two-electrode system vis-a-vis the Wenner system.

Section: Field Lay-outmentioning

confidence: 99%

Digital Linear Filter for Computing Type Curves for the Two‐electrode System of Resistivity Sounding*

Das

Verma

1980

“…(Das, Ghosh and Biewinga 1974) which present uncertainties and difficulties in quantitative interpretation.…”

Section: Introductionmentioning

confidence: 99%

Low‐pass Filtering of Noisy Field Schlumberger Sounding Curves Part Ii: Application*

Ghosh

Wadhwa

Shrotri

et al. 1986

The basic principles of the application of the linear system theory for smoothing noisedegraded d.c. geoelectrical sounding curves were recently established by Patella. A field Schlumberger sounding is presented to demonstrate first their application and validity. To achieve this purpose, firstly it is pointed out that the required smoothing or low-pass filtering can be considered as an intrinsic property of the transformation of original Schlumberger sounding curves into pole-pole (two-electrode) curves. Then we sketch a numerical algorithm to perform the transformation, opportunely modified from a known procedure for transforming dipole diagrams into Schlumberger ones. Finally we show a field example with the double aim of demonstrating (i) the high quality of the low-pass filtering, and (ii) the reliability of the transformed pole-pole curve as far as quantitative interpretation is concerned.

“…Das, Ghosh and Biewinga (1974) pointed out the "high-frequency'' nature of some causes of noise, and Bernabini and Cardarelli (1978) drew attention to the possible existence of strong " low-frequency " noise. Absence of noise undoubtedly facilitates the geophysicist's interpretative efforts.…”

Section: Introductionmentioning

confidence: 99%

“…However, experience has demonstrated that noise contamination of the field apparent resistivity sounding curves, often in the form of widely scattered data, has some probability of occurrence and in some situations is even the rule. Das, Ghosh and Biewinga (1974) pointed out the "high-frequency'' nature of some causes of noise, and Bernabini and Cardarelli (1978) drew attention to the possible existence of strong " low-frequency " noise.…”

Section: Introductionmentioning

confidence: 99%

Low‐pass Filtering of Noisy Schlumberger Sounding Curves Part 1: Theory*

Patella

1986

A contribution is given to the solution of the problem of filtering noise‐degraded Schlumberger sounding curves. It is shown that the transformation to the pole‐pole system is actually a smoothing operation that filters high‐frequency noise. In the case of residual noise contamination in the transformed pole‐pole curve, it is demonstrated that a subsequent application of a conventional rectangular low‐pass filter, with cut‐off frequency not less than the right‐hand frequency limit of the main message pass‐band, may satisfactorily solve the problem by leaving a pole‐pole curve available for interpretation. An attempt is also made to understand the essential peculiarities of the pole‐pole system as far as penetration depth, resolving power and selectivity power are concerned.