You are trying to use Electromagnetic Methods to investigate the structure of th

Question

You are trying to use Electromagnetic Methods to investigate the structure of the water table, which is in a sand and gravel unit that you estimate is at about 50 m depth. Above this (to the surface) is a clay unit with a conductivity of about 200 mS/m. The frequency of your system is 9800 Hz. Do you think electromagnetism is a good technique to use in this case? What if the upper unit was instead a till with conductivity of 5 mS/m? (Hint: think skin depth and pay attention to your units! You will want to convert to SI when you make your calculations. )

Explanation / Answer

Yes, electromagnetic technique work here. You can conduct survey both in time domain and frequency domain. Here you are using frequency for calculation. If you use the lesser frequecncy frequency your penetration depth will be more and vice versa ( Frequency and waveleng is inversely proportional to each other, as . frequency=speed of light/wavelength). The skin depth is generally a measure of the penetration of a plane electromagnetic wave into a material/Earth. It is the depth at which the intensity of the EM radiation inside the material/Earth falls to 1/e (about 37%) of its original value.

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