Abstract

The use of multibeam echo sounders (MBES) has grown more frequent in applications like seafloor imaging, fisheries, and habitat mapping. Calibration of acoustic backscatter is an important aspect of understanding and validating the performance of a MBES. For echo sounders in general, different calibration methodologies have been developed in controlled environments such as a fresh water tank as well as in the actual field of operation. While calibration in an indoor tank facility can bring excellent results in terms of accuracy, the amount of time required for a complete calibration can become prohibitively large. A field calibration can reveal the beam pattern for ship-mounted sonar systems, accounting for acoustic interferences which may be caused by objects around the installed transducers.

A method to determine the combined transmit/receive radiation beam pattern for a ship-mounted multibeam system was developed and tested at distances of up to 8 m using a Reason Seabat 7125 MBES inside the fresh water calibration tank of the University of New Hampshire. The calibration method employed a tungsten carbide sphere of 38.1 mm diameter as target suspended in the water column by a monofilament line and a Simrad EK60 split-beam sonar system to provide athwartship and alongship angular information of the target sphere position.

This aided standard sphere method is a potential candidate for field calibration of multibeam sonars. The results from the tests may be improved for field calibration by reducing angular offsets between MRAs of both systems and also by using a thinner monofilament line to avoid acoustic interferences. Despite the restriction in the covered angular region and reduced angular accuracy when compared to a conventional tank calibration procedure, it offers the advantage of being applicable to ship-mounted systems operating in the field, with significant reduced operation time.

Publication Date

12-14-2011

Document Type

Presentation

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