The main advantage of dipole dipole array is the possibility to acquire for one current dipole (current injection) several dipoles for the difference potential measurements. So, if your digital georesistivimeter is a multichannels instrument you can aquire simultaneously many quadripolar configurations with a reduction in acquisition times and then in acquisition costs. As a consequence you can performe acquisitions with a high data redudancy in the same time. For this reason the for example the marine or water electrical resitivity tomography is acquired with a cable in dipole dipole configuration. About the difference with respect each other configuration, it is generally suitable to have a relative greater depth penetration furthermore it is particularly indicated to resolve lateral resistivity variations contrarely the other arrays that generally have a relative greater vertical resolution in resistivity.

The most important in dpl-dpl is the fact that you will be in control of your current injection points comparison to the pole dipole array. But as Roberto said it is not a high array for vertical resolution for deep resolution compare to pole-dipole or pole-pole. If the survey condition (area) allowed you I recommended.

It has two major advantages.

1. Its operationally easy with no long cables

2. It has maximum resolution.

Thats why its so popular.

Sorry bat for land ERT surveys my opinion is that the Schlumberger- Wenner is the better array because it has a symmetrical cuadripolar configuration. So, the apparent resistivity measures are less affected by the path of the electric field potential lines; especially in highly heterogeneous subsurface media. My experience is that de dipole-dipole array creates vertical artifacts in the final resistivity model.

To mitigate the effect of the “asymmetry measurement”, the dipole-dipole survey must be acquired in both senses and then weighting the two measured pseudo-sections (apparent resistivity fields).

I am agree with the answer of Teresa about the problems of dip-dip configuration but the real advantage of dip-dip is mainly logistic-instrumental and the reduction in time and costs. When I have spoken of redundancy I properly refere to acquire multiple configurations included reciprocal measurements to exclude external/local influence on the measurements of apparent resistivity. About resolution and sensitivity it depends on what is our target if it is the stratigraphy or the lateral heterogeneity.

Unfortunately some times the best practices are sacrified for time and costs. I hope not in the research.

Dpl-dpl array is more stable than the others, if the surface is salty.

Dpl-Dpl array, where "a" is the dipoles length, and distance between dipoles is na, where n is integer. Dpl-Dpl array has better horizontal coverage than Wenner and Schlumberger (but less depth!), makes possible to use multichannel instruments effectively, but the signal is very weak in comparison to Wenner and Schlumberger. The voltage to be measured is reverse proportional to the cube of n. That's why dpl-dpl can be used only in clean places, without noise. Sensitivity of dpl-dpl is concentrated inside dipoles, it is sensitive to vertical boundaries.

for ALEX

the Dipole-Dipole DD array  the most suitable array for the ERT, the advantage is of this array is : sensible of horizontal variation of the resistivity value and most suitable for the detection the vertical structure like (fracture).

Dipole - Dipole has a good lateral resolution and is suitable for shallow studies. In depth the resolution of this array is lower. So using Dip - Dip array my be easy and fast but not always the best. For a good signal - noise ratio i can recommend Wenner and Schlumberger Arrays combined together (Wenner for the shallow part of section and Schlumberger for deeper part).

It may be a little to help you, but my experience has been that for multi-channel systems (Sting R8, Iris, ABEM), it is best to avoid dipole-dipole array because of the low signal strength relative to noise.  I prefer to use a schlumberger array for shallow and wenner for deeper surveys.  However, for large and deep exploration surveys using a Zonge GDP-32 or Phoenix system, the dipole-dipole is preferred for logistical reasons.

Loke and others have written extensively about optimized arrays, which maximize the resolution.  These optimized arrays do not adhere to the traditional array sets.  But with modern computer controlled systems, any array could be programmed.  

M. H. Loke has specified the reasons for choosing an array in Electrical Resistivity studies, please consult his articles.

The short answer is that it gives the highest spatial resolution and its logistically simplest. It does have disadvantages too, of course.

Dipole-Dipole array is now not preferred in Electrical Survey. It may give better depth of investigation but S:N ratio is low.

How to measure the S/N ratio from dipole-dipole array data? Is it the same with the % 0f RMS error from inversion result in Res2Dinv?

Dear Mr Lepong,

Signal to Noise Ratio (SNR) or better saying "signal level with respect to noise level" is actually related to the measured raw data, let's say that "SNR is a field data characteristic". However, the rms error represents the data misfit between the forward modeling calculations and measured apparent resistivity values. So, they are different from each other but not totally independent.

Ideally, the rms error should be zero. On the other hand, Hauck & Kneisel (2008) pinpointed that "a suitable rms error should be close to the field measurements error not zero because very low rms error is indicative of data over-fitting". Furthermore, there are some examples in the literature that an acceptable electrical resistivity image had a high rms error (around 55%!!!; i.e. doi:10.1016/j.enggeo.2009.07.004 ). So, no exact limits can be proposed about rms.

There are some ways to check whether a measured data seems to be OK or not by using: (i) repeated readings and (ii) reciprocal measurements. However, noise level cannot be correctly estimated in ERT. Stable noise cannot be recognized by (i). Also, the (ii) is not applicable for some type of arrays.

When we say, dipole-dipole is prone to more noise levels with respect to Schlumberger for example, we mean that:

"In a specific similar field condition (environmental noise, instrumental errors, same current intensity ranges, etc.), the dipole-dipole array is prone to more error with respect to Schlumberger because:

There are a lot of notes about the advantages and disadvantages of different arrays in 2D and 3D electrical surveying. I would recommend you to read the papers and notes of Dr. Loke and Dr. Rucker. The good resources for array characteristics are as follows:

• http://geotomosoft.com/coursenotes.zip
• doi:10.2113/JEEG20.3.207

• Article A Numerical Comparison of 2D Resistivity Imaging with Ten El...

Hope this comment would provide you useful points.

Regards,

S.R. Mashhadi

Please, about which depth you are taking about ?

is it such 40 meter or more than 200m ?

read the following articles

Dipole - dipole is best for vertical structures.....

Dipole-dipole can be implemented better for quasi-3D data acquisition.

Also, even it can be used successfully for sinkhole detection.

It is best deployed in field where vertical structures are present.

Dipole-Dipole configuration is highly sensitive in lateral horizontal variation. It is very good to follow any lateral variation, Seawater intrusion, Contaminations .....etc

Dear Alexandar,

It depends upon what objective you are trying to achieve. Have a large area to cover and want information regarding the lateral as well as vertical variations in resistivity dipole is the configeration to achieve that, but it has its own drawbacks regarding power source and cables but still it depends upon what you want to achieve. If we talk about ERT in that case dipole-dipole configeration definately helps delineate zones with some minor details whereas schlumberger and wenner gives generalise view of those zones