Protocols for calibrating multibeam sonar

TLDR

Multibeam sonar calibration offers advantages but faces outstanding problems, notably validating the performance of configured sonars. The study documents the development of protocols for calibrating multibeam sonar using the standard‑target method. The protocols were developed using three sonar systems (SIMRAD SM2000/90, 200‑kHz, and RESON SeaBat 8101 240‑kHz) at two facilities—a Woods Hole sea well and a University of New Hampshire freshwater tank—by measuring transfer characteristics, receiver response, and beam directionality. The principal outcome is a set of protocols detailing target positioning, receiver gain selection, system stability assessment, directional mapping of the receiving array, individual beam directionality, and near‑field response measurements.

Abstract

Development of protocols for calibrating multibeam sonar by means of the standard-target method is documented. Particular systems used in the development work included three that provide the water-column signals, namely the SIMRAD SM2000/90- and 200-kHz sonars and RESON SeaBat 8101 sonar, with operating frequency of 240 kHz. Two facilities were instrumented specifically for the work: a sea well at the Woods Hole Oceanographic Institution and a large, indoor freshwater tank at the University of New Hampshire. Methods for measuring the transfer characteristics of each sonar, with transducers attached, are described and illustrated with measurement results. The principal results, however, are the protocols themselves. These are elaborated for positioning the target, choosing the receiver gain function, quantifying the system stability, mapping the directionality in the plane of the receiving array and in the plane normal to the central axis, measuring the directionality of individual beams, and measuring the nearfield response. General preparations for calibrating multibeam sonars and a method for measuring the receiver response electronically are outlined. Advantages of multibeam sonar calibration and outstanding problems, such as that of validation of the performance of multibeam sonars as configured for use, are mentioned.