Land CSEM impulse responses in simple layered models

We argue that in a half space model with a single layer, the electric field impulse response at different offsets can be understood physically. Diffusive fields travel along paths like wavefields but are not localised in time. Each event that is measured comes from a path with the least attenuation, which corresponds to early arrival. The most prominent TE mode contribution to the detection of a subsurface layer comes from the coupling of the airwave with the subsurface. The most prominent contribution from the TM mode comes from the path through the resistive layer with almost vertical diffusion paths between the surface and the target. The arrival time of the peak of the event from a conductive layer can be understood from this reasoning. The arrival time of the peak of the event from a resistive layer can be understood from this reasoning when the offset is not too large compared with burial depth of the target layer. These predictions lead to estimates of depth to target layer with an error of less than 5% and the resistivity of the resistive layer of less than 50%. The information contained in the impulse responses suggests that inversion would yield good results.