A method to measure ship's underwater electric field from deck

Unexpectedly high underwater electric field (UEF) signatures of ships have been reported, and detection of ships by their UEF signatures is known to be effective. For the purpose of cost-effective and reliable method to estimate UEF signatures of actual ships in open sea, we developed a method to measure underwater electric potential (UEP) from the deck of the ship. Two reference electrodes were hung down into water from the deck side. By fixing one of the electrodes near the stem of the ship, we measured the UEP at several points by another electrode around the ship in the depth of one meter. We then measured the UEP for the two ships, and the ratio of UEP of two ships agreed with that of UEF signatures measured with the sensors on the seafloor. We confirmed that the proposed method to measure UEP of actual ships is effective.