19 June 2001




M. Harris
Naval Research Laboratory
Stennis Space Center, MS 39529-5004



The advent of multibeam bathymetry systems, which are capable of total seafloor ensonification, have made fundamental changes in hydrography. The new IHO S-44 standards challenge hydrographers to achieve even greater depth and position accuracy with multibeam systems. Using the multibeam system on the ORCA vehicle, incremental improvements have been made in each of these areas as demonstrated in a series of at sea survey tests. Improvements have been made to the system that allow: collection of data during turns; an order of magnitude improvement in heading measurement; and accurate measurement of vessel depth with respect to mean sea-level. Data collection during turns was achieved using a sensor that integrates inertial and GPS signals. Heading accuracy has been improved by going from a gyro based measurement system to a dual-antenna GPS phase differencing system. In addition to more accurate placement of soundings, especially in the outer beams, the system components are smaller and require less power than those replaced. Vessel depth measurements are made with a high-frequency altimeter, which also yields sea surface information including wave height, period, number and direction. An autonomous surveying capability has been developed to achieve the desired ensonification of the seafloor without over or under surveying an area. Coverage is based on the quality of data in the outer beams and the desired overlap in coverage. This paper describes changes made to NRL's multibeam system, and provides comparative results from system testing.

Sponsored by the Oceanographer of the Navy via SPAWAR PMW 185.

Published in the Sea Technology March 1999.
Naval Research Laboratory Contribution Number NRL/JA/7440 99-0002.
Journal Article