A Survey Spar System for Precision Offshore Seafloor Surveys

A new technique has recently been developed and used by the Navy's Civil Engineering Laboratory to precisely survey seafloor positions offshore in diver depths. The system combines a stiff, instrumented spar with conventional high accuracy methods for sighting from shore. The spar is anchored to the seafloor through a universal joint; tilt of the spar is measured in two planes. The position of the bottom of the spar is then calculated relative to the top, translating the surveyed location of the spar top to the seafloor. With this system two points were established and marked on the seafloor, in 70 feet of water over a mile and a half from the nearest land, to within ±3.6 inches with respect to First Order survey stations ashore. This represents a major advance in the state-of-the-art of seafloor surveying.