The design and development of a new generation of hydrographic and bathymetric swath survey systems presently under development by the National Ocean Survey is described. The Bathymetric Swath Survey System merges several recent developments in instrumentation into a system that will provide a quantum step forward in the art of bathymetric and hydrographic survey techniques. New instrumentation-a high resolution multibeam swath sonar, a Heave-Roll-Pitch sensor, real-time tide telemetry instrumentation, as well as navigation sensors and a powerful minicomputer-will form the core of system hardware. Software will sample all of the various sensors and provide for vessel navigation, sonar beam vertical depth and position determination, continuously-zoned real-time tide correction, and real-time bathymetric contour graphics, as well as archived raw sensor data.
The art of mapping the ocean floor has evolved very slowly. Land areas can be mapped to virtually any degree of accuracy and completeness using optical techniques provided by the well-established science of photogrammetry. Narrow-beam vertical echo sounders-the standard instrument used for ocean surveys-are functionally little more than efficient leadlines. In using echo sounding to produce nautical charts, only 2-5 percent of the area "surveyed" is actually seen or measured during the course of the survey. Even these measurements are frequently contaminated with gross, uncompensated errors caused by vessel heave, roll and pitch, requiring a tedious and subjective interpretation of graphic records to generate the data base used for, the compilation of the finished chart. Truly, ocean surveying today is as much an art as it is a science.
Over the years the practitioners of this art have taken special care to insure that the resulting charts were adequate for use by all commercial vessels (with drafts up to 30 feet). Indeed, they have done a uniformly remarkable job. The advent of the very large crude carriers (VLCC's) with drafts approaching 100 feet, however, has raised some concern as to the adequacy of existing charts and of survey techniques, especially in the near-shore waters along the U.S. west coast and Alaska. Although these waters are not very shallow, the underwater features are of a very rugged character and are difficult to accurately delineate with conventional survey instruments.
The solution to this problem has taken on a very high priority within NOAA's National Ocean Survey (NOS). The development of the Bathymetric Swath Survey System (BS3) by the National Ocean Survey is intended to move the art of bathymetric and hydro graphic surveying firmly into the realm of science. BS3 merges three key elements to achieve this transformation. A high resolution multibeam swath sonar allows 100 percent bottom coverage of a survey area. Recently-developed Heave-Roll-Pitch (H-R-P) instrumentation provides vessel attitude data necessary to reduce the sonar beam data to accurate vertical depths and horizontal positions. A powerful mini computer provides the computing horsepower needed to perform this data reduction and generate a bathymetric contour chart in real time. The system is now in operation on board the NOAA Ship DAVIDSON and will be evaluated for NOS charting operations this summer (1978).
