ENVS 216 - Electrical resistivity surveys

What is the electrode arrangement for the Wenner array?

4 equally spaced electrodes

IVVI

What is the electrode spacing for the schlumberger array?

Current electrodes are placed much further away than the voltage electrodes

IVVI

Which electrodes are required to move for each measurement in a Wenner array?

All 4 electrodes move

Which electrodes are required to movefor each measurement in a Schlumberger array?

Choose which electrodes to remain fixed then move the other 2

What is the electrode arrangement for the dipole dipole array?

Current and voltage pairs are separate

VV II

What is the square array used for?

Rapid, shallow surveys

What is the purpose of the square array being rotated around its centre?

Apparent resistivity is observed in several directions

Give 3 advantages of the wenner array?

Apparent resistivity is easily calculated in the field

Instrument sensitivity isn’t as important as other arrays

Small current required for a measurable voltage

Give 3 disadvantages of the wenner array?

All electrodes need to be moved for each measurement

Longer current cables are needed

The array is sensitive at near surface which can skew deeper electrical measurements

Give 3 advantages of the Schlumberger array?

Fewer electrodes need to be moved per measurement

Voltage cable lengths are shorter

Better resolution and probing depth

Give 2 disadvantages of using the Schlumberger array?

Longer current cables required

Recording instrument needs to be very sensitive

Give the primary advantage of the dipole dipole array?

Short wire lengths so easier to set up in the field

What is a large disadvantage of the dipole dipole array?

A large generator is needed to transmit a large current for deep measurements

What is a vertical electrical sounding or expanding array?

Current and voltage electrodes keep their relative spacing but are expanded around a fixed central point

Does current reach shallower or deeper as the electrodes are moved apart in VES arrays?

Current reaches deeper

What is a constant separation traversing or electrical profiling array?

The current and voltage arrays stay at the same separation and are moved along the profile

Are CST arrays shallow or deep surveys?

Shallow surveys

What are CST arrays ideal for searching for?

Buried walls, etc

Which type of survey is an automated system that switches the electrodes and you can just hit go and leave?

Electrical resistivity tomography

Give 3 general advantages of electrical resistivity surveys as a whole?

Cheap, quick, and versatile

Give 3 disadvantages of electrical resistivity surveys as a whole?

Current flows through the voltage circuit

Edge effects

Off axis effects