Towfish - Klein 5000 SERIES Operation And Maintenance Manual

1-5
Theory of Operation
The Series 5000 departs from previous multibeam systems in that the swath
forming process is implemented digitally using digital signal processing (DSP),
rather than analog delay lines, phase shifters, or multipliers and adders. The
primary advantage of this technique is a reduction in the size and weight of the
towfish. This affords a concomitant reduction in the size of the required survey
vessel and ancillary equipment, such as a winch and crane. Other advantages
include more flexibility in the swath processing, allowing software control of
operating parameters. Previously this would have required hardware changes.
The Series 5000 architecture is composed of the towfish, the tow cable, the
computer, and the TPU. The towfish contains the transducer arrays and electronic
subsystems for transmission, reception and data acquisition, and telemetry. The
towfish also includes standard and optional sensors for the monitoring of towfish
position and motion dynamics, pressure, depth and altitude (acoustically
measured), temperature, and other pertinent information.
The tow cable is simply a coaxial cable that provides power transfer and duplex
communications between the towfish and the TPU.
The TPU processes the data from the towfish, producing multiple simultaneously
focused swaths. The TPU outputs this data via a proprietary parallel port. Sonar
processor control of the TPU is done via the local area network (LAN).
1.4.2

Towfish

The towfish is composed of the towfish housing, which has external brackets for
cable attachment, the transducer arrays (one for each side), the nose cone, the tail
section, and a pressure housing containing attitude and environmental sensors and
electronics. In a typical operation the towfish is towed behind the survey vessel by
means of the tow cable. The depth at which the towfish runs below the surface of
the water is a function of both the length of the deployed cable and the tow speed.
NOTE The transducers are side specific and are not interchangeable.
The two transducer arrays are each composed of 12 piezoelectric ceramic
sub-arrays that operate as both transmit and receive elements. Each set of
12 sub-arrays is arranged into a continuous line array spanning an overall aperture
of 1.2 meters.
The towfish electronics is divided into five individual boards: a Transmitter board,
two Receiver boards, a Sensor Interface board, and a Multiplexer board. A block
diagram of the towfish is shown in Figure 1-3.