Absolute magnetic viscosity determination using time-domain electromagnetic devices
Résumé
Anthropogenic activity results in an increase of magnetic susceptibility of the uppermost layer (topsoil) of the ground, but the origin of this increase is not linked systematically to past human activity and may derive from natural pedological processes. The use of a new magnetic parameter can be relevant to allow a better distinction between anthropogenic and natural effects. We propose the use of magnetic viscosity. It can be measured by either time-domain instruments (TDEM) or by quadrature susceptibility in the frequency domain, but in both cases absolute measurements must be performed. The calibration process to be applied to TDEM instruments is described and applied to an 'old' commercial device. The results obtained on a test site are then presented to illustrate that the absolute viscosity measurement is now possible.