Sea Beam Mapping Systems

Abstract

The introduction to the oceanographic community of deep ocean, multibeam mapping systems such as Sea Beam has had a profound effect both on the way we view the sea floor and on the way in which sea floor surveys are conducted, particularly with regard to open ocean navigation. These systems provide more than a hundred-fold increase in survey resolution as well as practical potential for complete survey coverage with deep water resolution of 100–200m. Thus they have not only placed severe demands on shipboard navigation but have also by themselves permitted highly accurate terrain-following navigation in areas previously surveyed. Map production from these systems generally relies on topographic matching for final adjustment of ship navigation, even when extremely accurate navigation, such as GPS, is available. There are now a dozen Sea Beam installations worldwide (5 in the U.S.) with each system contributing on the order of 1/2 gigabyte of sea floor survey data each year. This paper will detail some of the history of multibeam sea floor mapping as well as some of the promises and problems of these systems. The systems installed and operated aboard the R/V’s CONRAD and ATLANTIS II by the URI/NECOR Sea Beam Facility will be described. The CONRAD is a well-equipped geophysical research ship with multichannel and precision gravity capabilities. Its navigation equipment includes Loran-C, two-axis doppler speed log, SATNAV and GPS with atomic clock. The ATLANTIS II is the support ship for the submersible ALVIN, and is equipped for acoustic transponders and range/bearing navigation in addition to speed log, Loran-C, SATNAV and GPS.