Soil electrical resistivity measurements for a wind turbine location

[Cesme]

Hello everyone, I wonder if 2 90 degree cross measurements (traverses) are sufficient in the wind turbine field? According to BN 50522, spans (a = 1 m - 1.5 m - 2m - 3m - 4.5m - 6m - 9m - 13.5m) are recommended as amax = 13.5 m. Does anyone have a different comment or advice on this subject?

 

[7anoter4]

According to EN 50522 Annex L[informative] Measurements for and on earthing systems , L1 Measurements of soil resistivity have to be carried out using a four-probe method for example, Wenner method for different depths.
There are different ways to measure the resistance and impedance to Earth of an electrode or grid depending on extent of the system and the degree of interference.
When using the fall potential method, the earth electrode, the probe and the auxiliary electrode has to be in straight line and the minimum distance of the probe has to be 20 m [up to 2.5 the total extend of the system] and the auxiliary electrode 40 m minimum [up to 4 times the total extend of the system].
See-for instance:

https://iris.unipa.it/bitstream/10447/370130/7/postprint%20Fall.pdf