First Land Application of the Differential Electrical Dipole Method together with Transient Electromagnetics

The newly developed DED-transmitter consists of two horizontal electrical dipoles that share a common central electrode which has one polarity, while the outer ones have the opposite polarity. Thus, the current in each dipole flows in opposite directions. The differential signal is recorded by electrical receivers at a certain distance. This feasibility study, realized along the beach of de Panne in Belgium, is the first land-based application of the DED system of its kind. The freshwater distribution has a thickness variation of 8–15m in a depth of up to 30m. 24 DED measurements were conducted at the beach at low tide, utilizing two 75m transmitter dipoles in an inline configuration parallel to the beach. Six transmitter locations were assembled parallel to the beach with a spacing of 50m along with four electrical receiver stations at different offsets. Additionally, 40 inloop TEM stations were measured. Previously performed 1D modelling studies suggested an interpretation of the DED Step-On signal as more suitable compared to the DED Step-Off signal. A joint inversion algorithm is for DED and TEM data was developed. Based on these results a freshwater distribution underneath the Belgian coastline is confirmed with a varying thickness between 8 and 30m.