Quantifying the Effect of the Water Layer in Shallow Marine Active Source EM

The water layer above the source and receiver in active source marine EM surveying is known to affect the measured response with a significant amount of energy travelling from the source to the receiver through the air. This has the effect of reducing the sensitivity to resistivity variations in the subsurface. This is especially true in shallow water. The use of a transient source waveform allows for a degree of temporal separation of the water layer and subsurface responses; this separation increases for decreasing water depth and decreasing subsurface resistivity. In the frequency domain no such separation exists and the airwave is only suppressed by increasing water depth.