Table of Contents
International Journal of Oceanography
Volume 2015, Article ID 589463, 11 pages
http://dx.doi.org/10.1155/2015/589463
Research Article

Effects of Noise and Absorption on High Frequency Measurements of Acoustic-Backscatter from Fish

Tokyo University of Marine Science and Technology, 4-5-7 Kounan, Minato, Tokyo 108-8477, Japan

Received 7 June 2015; Accepted 12 October 2015

Academic Editor: Renzo Perissinotto

Copyright © 2015 Masahiko Furusawa. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Quantitative echosounders operating at multiple frequencies (e.g., 18, 38, 70, 120, 200, 333, and 710 kHz) are often used to observe fish and zooplankton and identify their species. At frequencies above 100 kHz, the absorption attenuation increases rapidly and decreases the signal-to-noise ratio (SNR). Also, incomplete compensation for the attenuation may result in measurement error. This paper addresses the effects of the attenuation and noise on high frequency measurements of acoustic backscatter from fish. It is shown that measurements of a fish with target strength of −40 dB at 200 m depth are limited by SNR to frequencies up to about 100 kHz. Above 100 kHz, absorption coefficients must be matched to local environmental conditions.