If we make a near-surface resistivity survey, the measured apparent resistivities for each AB electrodes spacing will present a log-normal distribution?
In order to evaluate soil resisivity, a number of measurements are taken at conventional spacings, say at 1,2,4,8,16...meters. Only the average at each spacing is then used for soil beaviour evaluation. I remember having read that the set of resistivities for the same spacing show a log-normal distribution.
No, I do not remember where I saw it. But is is very, you can take actual measurements, which you certain have, and verify if this applies, or not!
Daniel
I have already tryed this. What happens is that it is needed a lot of measurements, in order to have a sample with statistical representativity, allowing the construction of a clear histogram. Also, it would be intesting to have a reference stating this.
If the basic objective is to measure near surface lateral inhomogeneity in terms of resistivity variability, the best method is to go for dipole-dipole configuration and prepare pseudosection to get a tomographic view of the litho-unit. The electro-facies obtained thereby gives a fairly good comparison with the lithofacies. The other way is to conduct sounding at different locations on a profile. It will be a log-log plot with AB/2 and the apparent resistivity. If at two ends of the profile two boreholes are drilled and the actual lithofacies is constructed with extreme care, then the sounding done at those points can be calibrated properly by making use of the Interpex software (A highly user friendly software). Subsequently, correlation can be undertaken for the soundings done at the intermediate locations. A sedimentological background with process based understanding to helps a lot for realistic modeling of the electrofacies.
To the question of the resistivity distribution and small-scale heterogeneity I can recommend the PhD thesis of my colleague Jan Igel named "On the Small-Scale Variability of Electrical Soil Properties and its Influence on Geophysical Measurements" that can be found under
http://publikationen.ub.uni-frankfurt.de/frontdoor/deliver/index/docId/586/file/IgelJan.pdf
In his investgations he found a log-normal resistivity distribution for many cases.
Dear Thomas, your information will be very usefull for my Doctoring Thesis - resistivity models by means of geostatistics for application on electrical grounding studies. Thank you very much.