Distortions of EM transients in coincident loops at short time-delays

Transient electromagnetic measurements with short time-delays of transients are used for solving different problems within the upper part of a geoelec tric section. However, it is necessary to take into consideration distortio ns connected with self-transients within the transmitter-receiver system. F rom the practical point of view, it is important to estimate the minimum ti me-delay after which these distortions may be neglected. We present such an estimation which uses a simple approximation method for a single-loop (or coincident-loop) configuration. For common values of the loop size (10 m x 10 m to 40 m x 40 m) and of the resistivity of a homogeneous half-space (1- 100 Omegam), the minimum time-delay beyond which we can use a standard inte rpretation is in the range of 2-10 mus. This is equivalent to a minimum dep th of investigation in the range of 1-30 m.