Calculating Time-Domain Controlled Source Electromagnetic Signals with MARE2DEM

The time-domain controlled source electromagnetic (TD-CSEM) method is commonly used to map shallow regions of the seafloor from several metres up to a couple hundred metres penetration depth. The method is effective in detecting shallow conductivity anomalies within the seafloor. Compared to the commonly applied frequency-domain controlled source electromagnetic method, the time-domain application is particularly effective in shallow marine environments, where the signal is less susceptible to the masking issue of the well-known airwave effect. However, the current interpretation of TD-CSEM data is mainly based on one-dimensional inversion, which creates problems in accurately mapping the true bathymetry. Here we present results of a 2D goal-orientated, adaptive finite-element modelling based on the MARE2DEM software that is freely available to academia for frequency-domain applications. A comparative modelling study using semi-analytical solutions for a simple 1D conductivity model shows that the time-domain developments can accurately calculate the main components of a horizontal dipole source in both the inline and broadside components. Merely, the vertical electric field is inaccurate at late times of the step-off current excitation and may need a more accurate discretisation approach