WHAT IS WANNER AND SCHLUMBERGER ARRAY.

What is Wanner Array
The Wanner Array is a type of electrode configuration for a DC resistivity sunray and is defined by its electrode array geometry.

ADVANTAGE AND DISADVANTAGE OF WANNER AND SCHLUMBERGER ARRAY.

ADVANTAGE OF WANNER ARRAY

1. The advantages of Wanner Array are that the apparent resistivity is easily calculated in the field and the instrument sensitivity is not crucial as with other array geometries. (Keller, 1966) Dipole method for Deep Resistivity Studies.
2. Relativity small current magnitudes are needed to produce measurable potential differences

DISADVANTAGES OF WANNER ARRAY

1. The disadvantage of Wanner Array are that each for each sounding all of the electrode have to be moved to a new position in order to image deep into the earth, it is necessary to use longer current cable; handling the cable and electrodes between each measurement can be cumbersome  especially in difficult terrain.
2. The Wanner Array is also very sensation to near surface in homogeneities which may skew deeper electrical responses.

THE ADVANTAGES OF SCHLUMBERGER

1. The dvantage of Schlumberger array are that fewer electrode need to be moved for each sounding and the cable length for the potential electrode is shorter.
2. Schlumberger Sounding generally have better resolution greater probing depth and less time-consuming field deployment than the Wanner Array. EPA 1993 Use of Airborn Surface and Borehole Geographical Techniques Side.

THE DISADVANTAGE OF SCHLUMBERGER

1. The disadvantage of Schlumberger are that long current electrode cable are required, the recording instrument need to be very sensitive and the array may be difficult or confusing to co-ordinate amongst the field crew.

APPARENT RESISTIVITY

The resistivity of homogeneous isotropic ground that would give the same voltage current relationship as measured. Direct current apparent resistivity, Pa, is an Ohm’s-law ration of measured voltage V to applied current I, multiple by a geometric constant K which depends on the electrode array: pa=KV/1. Usually has unit of ohin meters.

With electromagnetic methods quantities such as module of the electric and magnetic field intensities (E and H) are measured at a certain equation. However, use of this are equation for a heterogeneous subsurface yield the apparent resistivity.  

where PHS=resistivity of homogenous half space. F is a function of V=observed voltage and VHS=voltage for a half=space. Asymtotic define such as late-time and early-time apparent resistivity are sometimes used for apparent resistive value over a limited range of measurement parameters. For some EM models apparent resistivity maybe undefined or multivalued see spies and Egger (1986) and strack (1992).

The resistivity recorded by an electrical log that differs from the time resistivity of the formation because of the presence of mud column, invaded zone, influence of adjacent beds e.t.c.

REFERENCES

Spies, Brain R: Eggers, Dwight E (1986) the use and misuse of apparent resistivity in electromagnetic method “Geophysics (Society of Exploration Geophysics) 5, (7): 1462-1471 do;10:1190/1/442194.

Stract (1992) Exploration with deep transient electromagnetic, Amsterdam New York: Plservier. ISBN 978.044489541:)

References: EKP 1993) use of airborne surface and borehole geographical Technics art contaminate side.

UW Medison N.D: Introduction to Applied Geophysics.

Merrison and Gasperkov a 2012 DC Resistivity and in Field System Data Processing and interpretation.

DC-Resistivity Survey (Wanner Array of Electrode Configuration for a Deep Resistivity Sunray and is Defined by it Electrode Array Geometry.

Morison and Gasper, Kov a 2012 DC Resistivity and IP field systems. Data processing and interpretation.