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Enlightening Research

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Non-contact electromagnetic profiling

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Traditional EM methods have difficulty focusing on targets buried at the depths less than 5 m and can provide only local measurements of electrical conductivity or resistivity. At the other extreme, most ground-penetrating radar systems, although generate continuous electrical profiles, can only investigate the top meter or so when salts or clay minerals are present in the soil. Hence, in many applications there is a depth range where neither traditional EM nor GPR systems are adequate. The advantages of NEP method are that it automatically records continuous profiles of electrical resistivity and allows easy changing inter-coil spacing to survey different soil depths. A generator constantly excites electromagnetic field through the two radiating antennas. The antennas form the transmitting coil through the soil. Parameters of a secondary electrical field created in the soil are received by the receiving coil and automatically recorded in a graphical form of continuous electrical resistivity profile in the receiver-register block. The NEP equipment operates on user-defined frequencies of the primarily electromagnetic field within the range from 12.5 to 14.5 kHz. Due to the low frequency, the properties of the created electromagnetic field are similar to those of the stationary electrical field created by the methods of constant current (VES and EP). Thus, we can easily vary the depth of electromagnetic profiling by changing the distance between radiating and receiving antennas. The minimal depth of 0.4 m can be investigated with the method at a 5-m spacing between radiating and receiving antennas. Layers as deep as maximum 20 m can be investigated.

All the methods used in this study have different advantages and limitations. Therefore, no single method could be a priori recommended as universal for all soil applications. Three methods of the stationary (SP, EP, and VES) and one methods of the non-stationary electrical fields (NEP) were tested in different applications in soil genesis studies, civil and environmental engineering, agriculture, and soil monitoring. Detail description of the applied methods can be found in Pozdnyakov et al., 1996; Pozdnyakova, 1999 - Electrical properties of soils ; and Pozdnyakova et al. 2001 - Application of Geophysical Methods to Evaluate Hydrology and Soil Properties in Urban Areas.