Simple Profiles

SIMPLE  PROFILING: The simplest and most common type of profiling is to do a simple Wenner array reading and then move the electrodes forward and take another reading, etc. The apparent resistivities are plotted at the midpoint of each array. The array can be aligned in the direction of profiling or normal to that direction. Surveying with the array aligned in the direction of profiling is faster. If the survey is to locate a soil or geological boundary normal to the profile, then a more distinct anomaly will be obtained if the array is also normal to the profile. This takes more field time but makes the interpretation far easier.


If the Wenner array is used, an “a” spacing of about one and one-half to two times the depth of interest should be used. A more precise selection of “a” spacing can be made by doing a depth sounding and selecting an “a” spacing where the curve indicates a rapid change in apparent resistivity with increasing “a” spacing.


If the Wenner spread is aligned in the direction of profiling, a convenient advancement of the spread is three times “a”. The lead electrode of one observation becomes the trailing electrode of the next observation. For more detail, an advancement of only two times “a” or even one “a” can be used. For reconnaissance surveying an advancement of more than three times “a” can be used.


Appendix M presents a profile surveyed for both resistivity and IP using an “a” spacing of one foot.

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