Definition of signal-to-noise ratio and its critical role in split-beam measurements

The signal-to-noise ratio (SNR) plays a critical role in any measurement but is particularly important in fisheries acoustics where both signal and noise can change by orders of magnitude and may have large variations. "Textbook situations" exist where the SNR is clearly defined, but fisheries-acoustic measurements are generally not in this category as signal and noise come front a wide range of sources that change with location, depth, and ocean conditions, This paper defines the SNR and outlines its measurement using splitbeam data. Its effect on target-strength (TS) measurements is explored. Recommendations are given for the routine use of the SNR in fisheries-acoustic measurements. This work also suggests a new equation for TS estimation that is important at low SNR. Crown Copyright (C) 2004 Published by Elsevier Ltd on behalf of International Council for the Exploration of the Sea. All rights reserved.