Well, it depends on what you define to be "short cable length". Some "manufacturers" offer 4-electrode devices, with electrodes set up in square or rectangular arrays. If such devices are properly designed, it is conceivable that they operate on the principle of the Habberjam square-electrode array. It is possible to convert the square-array measurements to equivalent co-linear Schlumberger or Wenner pseudo-measurements and simplistically interpret them in this capacity, within the limitations of these methods. However, the penetration depth of any given square-array is limited by the size of the array (or the spread of the equivalent co-linear arrays) the only way to increase penetration is to expand the square-array outwards (which requires physical labour). Thus, if, the device uses DC or ELF current and the side of the array is, say, 20m, the penetration is limited to no more than a few meters and there is NO PHYSICS that will allow penetration to depths of 200-300m irrespective of the strength of the injected current. If the cable is longer than a few hundreds of meters, and the current is sufficiently strong (which usually isn't), penetration to such depths may be possible. Other "manufacturers" may offer 4-electrode devices that can only operate in co-linear mode and require two operators to move the electrodes and one operator to take the measurements. In all cases the depth of penetration may increase only in a labour-intensive / low productivity fashion.

In general, manufacturers of "tiny portable instruments" never stand up to their promises and their products typically underperform - they are usually low-tech machines with low output power, simple or simplistic user and computer interfaces and elementary display and analysis software, but dressed up to look impressive and magnificent. Quite often, they are much more expensive than what is justified by their quality and usefulness. They may be OK for some kinds of amateur work but they are generally of no value to professionals.

Finally, I suggest that one should be very vigilant in appraising the claims made by manufacturers of such devices, especially when they are flamboyant and include detection of “metallic objects” and “treasure”. One will notice that they are usually big on promises but seldom explain the physical principles on which their instruments work, limited to vague generalities at best, or made-up “physics” (para-science) at worst. They also do not provide reviewed literature of case-studies to demonstrate the performance of their products.

Azimuthal square array is a suitable method for aquifer and fracture zone identificaiton.

Regarding your query about depth of investigation of penetration:

In dc resistivity sounding/profiling equipments  whatever the electrode array used or current is injected in the earth,  you can get the information from maximum depth of AB/2. The current flow between current electrodes in hemispherical  manner. Thus, maximum depth will radius of that sphere i.e AB/2.  It is better to assume that AB/4  may be possible depth from where you can get the information. However, it may be even lesser (Ab/8) as the assumption of stratified homogeneous earth is rarely fulfilled in real world. Thus, you have to plan your survey accordingly depending upon the priori information of geology or previous geophysical work carried out by other field geophysicists. For getting information  from deep subsurface, you will need high current source as well long cables. 

Could you give the reference about   "tiny portable instruments". May be it is not DC unit at all.

MT sounding needs 4 electrdoes for two MN lines plus two magnetic sensors. In this case you can receive very deep soundings with short array.

First of all, the physics and the principles are the same, irrespective of the type of resistivity meter. Like Dr. Tzanis has indicated, you have to be careful and knowledgeable to know and understand the claims of the company personnel.

The principles are the same, irrespective of the type of resistivity meter...

Dear Mr.Pradad,

Thank you very much for the response.