An integrated acoustic seabed survey system was used during the summer of 1975 in water depths of approximately 320 meters off the Coast of Labrador. A single towed vehicle housed dual channel side scan transducers, preamplifier, a variable frequency sub-bottom profiling array, a 200 kHz high resolution echo sounder transducer and all interconnecting cables to mate with a single double armored multiconductor tow cable. Equipment on board included a heavy duty winch with slip rings and remote control, all necessary electronic components and recorders and a 90 kHz "over-the-side" echo sounder to measure overall water depth.
The system was successfully employed in a survey off Labrador, for the purpose of locating and mapping iceberg scours. Operating at towing speeds of 4 knots or more, in water depths of 150 to more than 320 meters, records were obtained showing iceberg scour depth and shape in sufficient detail to provide an indication of scour age. The system was installed aboard ship in less than 24 hours and was operated for a two week period without interruption due to weather, mechanical or electronic failure.
Important aspects of the system include towing characteristics, power requirements, sub system synchronization, ease of mobilization and personnel requirements. Each of these areas are discussed and sample records taken during the survey are presented which demonstrate the advantages of using one integrated, multiple sensor acoustic survey system.
Acoustic techniques have gained significant prominence in the area of high resolution studies of the seafloor and sub bottom sediments during the past five years. Special systems, each designed to perform a specific function have been developed to acquire information for either geological or engineering purposes. Three classes of acoustic systems are described briefly below.
Sub Bottom profiling Systems, generally operating in the frequency range from a few hundred herz up to about 12 kHz are now used quite extensively for obtaining high resolution records of sub bottom sediments to a depth of 200 – 300 feet beneath the bottom. (Figure 1) This class of equipment includes sparkers, boomers, and discrete frequency sources, each of which provide useful information for different applications. As operating frequency is increased, resolution of sub bottom detail is improved while bottom penetration is reduced. For this reason it is generally desirable to operate at high a frequency as possible, consistent with the type of bottom material being surveyed and the penetration which is desired.
Side Scan Sonar Systems are used to look at the bottom for a distance of several hundred meters from one or both sides of the survey vessel, or towed fish. (Figure 2) Operating at a relatively high frequency, generally in the range from 50 kHz to 200 kHz, resolution is quite good and objects of a few inches in diameter can be seen quite clearly on side scan records.
High frequency bathymetric echo sounders have been in use for many years for the purpose of charting water depths.