We compare selected marine electromagnetic methods for sensitivity to the presence of relatively thin resistive targets (e.g., hydrocarbons, gas hydrates, fresh groundwater, etc.). The study includes the conventional controlled-source electromagnetic method, the recently introduced transient electromagnetic prospecting with vertical electric lines method, and the novel marine circular electric dipole method, which is still in the stage of theoretical development. The comparison is based on general physical considerations, analytical (mainly asymptotic) analysis, and rigorous one-dimensional and multidimensional forward modelling. It is shown that transient electromagnetic prospecting with vertical electric lines and marine circular electric dipole methods represent an alternative to the conventional controlled-source electromagnetic method at shallow sea, where the latter becomes less efficient due to the air-wave phenomenon. Since both former methods are essentially short-offset time-domain techniques, they exhibit a much better lateral resolution than the controlled-source electromagnetic method in both shallow sea and deep sea.
