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Materials and Methods

Electrical geophysical methods used in this study can be broadly classified as methods measuring natural electrical potentials of the ground without introducing additional electricals field and methods utilizing artificial electrical or electromagnetic fields to measure soil electrical parameters. Method of self-potential (SP) measures the naturally existing stationary electrical potentials in the soil. Vertical electrical sounding (VES) and electrical profiling (EP) methods measure electrical resistivity or conductivity of soil to any depth when a constant electrical field is artificially created on the surface. VES and EP methods as well as laboratory method of measuring electrical resistivity in soil samples are based on four-electrode principle, but vary considerably in electrode array lengths and arrangements, which makes the methods suitable for different applications. The VES, EP, and SP methods evaluate parameters of the stationary electrical fields in soils. All the methods of stationary electrical fields require grounding electrodes on the soil surface; therefore, measurements with these methods can be made only in agricultural fields, rural areas, or in the laboratory in soil samples.

Electromagnetic induction methods (EM), non-contacted electromagnetic profiling (NEP), and ground penetrating radar (GPR) introduce electromagnetic waves of different frequencies into soils. The EM, NEP, and GPR evaluate properties of the non-stationary electromagnetic fields in soils. All the methods of non-stationary electromagnetic fields are mobile. The methods do not require a physical contact with the soil surface and can measure electrical resistivity or conductivity in soils covered with firm pavement. The NEP method, which we used in this study, has been specifically designed in Russia for shallow-subsurface environmental studies (Pozdnyakova et al., 1996).