Time-domain electromagnetic sounding in Arctic water areas

Time-domain electromagnetic (TDEM) sounding method is effectively used in shallow marine waters all over the world, including the Arctic shelf, where the main object of study is the permafrost layer. A generalized geoelectric model of the Arctic shelf section is presented, which is based on the results of studies conducted by the authors, using archival information from available sources, and contains three main layers: unfrozen bottom sedimentary layer, permafrost layer and subpermafrost layer. Algorithms for solving direct and inverse problems of TDEM are briefly described, also including those using the polarization properties of the layers. Typical curves of apparent electrical resistance of TDEM (TDEM curves) are constructed, corresponding to geoelectric models of Arctic waters for three zones - the open sea, the transit zone and the river mouth. The curves qualitatively reflect the dependence of resistance on depth, except for the case of the most highly resistive section containing a polarizing layer, when the curve is strongly distorted. A series of model experiments were carried out to solve the inverse problem within the framework of a five-layer model. It was shown that when obtaining possible equivalent models that differ from the true one (created by the authors using known parameters), their number can be reduced by fixing the parameters of the water layer, thereby improving the modeling results. The effects associated with the polarizability of the sub-permafrost layer, which significantly complicate interpretation, but quickly fade with an increase in the thickness of the seawater layer, were analyzed.