by
K.A. Johannesson, MIOA
Electronics/Acoustics Engineer
FAO Acoustics Expert
R.B. Mitson, FIOA
Electronics/Acoustics Engineer
FAO Consultant
FAO FISHERIES TECHNICAL PAPER 240
FIRM/T240
FAO - FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
Rome, 1983
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The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. |
M-42
ISBN 92-5-101449-3
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying or otherwise, without the prior permission of the copyright owner. Applications for such permission, with a statement of the purpose and extent of the reproduction, should be addressed to the Director, Publications Division, Food and Agriculture Organization of the United Nations, Via delle Terme di Caracalla, 00100 Rome, Italy.
© FAO 1983
This electronic document has been scanned using optical character recognition (OCR) software and careful manual recorrection. Even if the quality of digitalisation is high, the FAO declines all responsibility for any discrepancies that may exist between the present document and its original printed version.
1.1 Development of Acoustic Methods in Fisheries
1.2 Contents of this Manual: Its aim and scope
2.1 Direct Electrical Current (DC)
2.2 Alternating Electrical Current (AC)
2.3 Root-Mean-Square (rms) Values
2.4 Acoustic Pressure and Intensity2.5.1 Power and Intensity Ratios
2.5.2 Voltage and Pressure Ratios2.6 Speed and Absorption of Acoustic Waves
3. PRINCIPLES OF INSTRUMENTS FOR FISHERIES ACOUSTICS
3.1.1 Time base
3.1.2 Transmitter
3.1.3 Transducers and Acoustic Beams
3.1.4 Receiver Amplifier
3.1.5 Displaying and Recording Signals
3.1.6 Recording Paper3.2 The Analog Echo-integrator
3.2.1 Demodulator
3.2.2 Amplifier
3.2.3 Threshold
3.2.4 Depth and Interval Selection
3.2.5 Voltage Squarer
3.2.6 Voltage Squared Integrator
3.2.7 Display of Integrated Signals3.3.1 Simrad QD Integrator
3.3.2 Biosonics DE1 120 Integrator
3.3.3 AGENOR Integrator
3.3.4 Furuno FQ Integrator3.4.1 Multimeters
3.4.2 Oscilloscopes
3.4.3 Signal Generators
3.4.4 Electronic Counters
3.4.5 Hydrophones
3.4.6 Projectors
3.4.7 Calibration of Test Instruments
4. FORMING THE ACOUSTIC EQUATIONS
4.1 Power and Source Level
4.2 Decrease of Intensity with Distance
4.3 Variation of Intensity across the Beam
4.4 Single Fish as Acoustic Targets
4.5 Fish Schools as Simple Acoustic Targets
4.6 An Equivalent Transducer Beam
4.7 Noise Level
4.8 Summary of Acoustic Equation Terms4.8.1 Source Level
4.8.2 Receiving Sensitivity
4.8.3 SL + SRT
4.8.4 Transmission Loss
4.8.5 Target Strength
4.8.6 Volume Back-Scattering Coefficient
4.8.7 Reverberation Level
4.8.8 Beam Factor
4.8.9 Biomass Calculation
5. ACOUSTIC PROPERTIES OF FISH
5.1 Target Strength
5.2 Measurement of Fish Target Strength5.3 Fish Size and Target Strength Dependence
5.4 Fish Tilt Angle
5.5 Acoustic Frequency and Fish Target Strength
5.6 Fish School Target Strength
6. CONCEPTS OF ACOUSTIC ESTIMATES OF AQUATIC BIOMASS
6.1 Measurement of Volume Back-Scattering Strength
6.2 Mean Volume Back-Scattering Strength (MVBS)
6.3 Measurement of relative density
6.4 Measurement of Absolute Density
6.5 Determination of Mean Fish Density in a given Area
7.1.1 Standard Targets
7.1.2 Calibration by Range (R) and Voltage (V) measurements
7.1.3 Hydrophones/Projectors
7.1.4 Intership Acoustic Calibration
7.1.5 Live Fish Calibration7.2.1 Transmitter/transducer
7.2.2 Receiver/Time Varied Gain
7.2.3 Time Varied Gain Amplifier Calibration
7.2.4 Integrator
8. ORGANISATION OF WORK AND PROCEDURES
8.1 Importance of Team Work
8.2 Planning and Design of Surveys8.2.1 Objectives and Background Information
8.2.2 Operational Aspects
8.2.3 Survey Design8.3 Standardisation of Control Settings
8.4.1 List of Equipment Factors
8.4.2 Data Recording and Storage
9. SOURCES OF ERROR IN THE ESTIMATES
9.1 Systematic/Random Errors
9.2 Equipment Operational Errors9.2.1 Bottom Pulse Failure
9.2.2 Layer Selector Spike
9.2.3 School Generated Bottom Stop Pulse
9.2.4 Secondary Echo Interference
9.2.5 Instrument Drift
9.2.6 Attentuation by Bubbles9.3.1 Biological Noise
9.3.2 Electrical Noise
9.3.3 Receiver Amplifier Self-noise
9.3.4 Acoustic Noise
9.3.5 Ship Noise
9.3.6 Miscellaneous Sources9.4.1 Near Surface Layer
9.4.2 Near Bottom Zone
9.4.3 Inaccessible Fish Distribution9.5 Vessel Avoidance (variability with depth of fish)
9.6 Other Errors9.6.1 Motion Induced Errors
9.6.2 Acoustic Beam Overlap
9.6.3 Shadowing Effects
9.6.4 Resonance of Organisms
10. DATA ANALYSIS FOR FISH ABUNDANCE ESTIMATION
10.1 Data Handling and Processing
10.2.1 Scaling Factor 'C'
10.2.2 Simple Random Sample
10.2.3 Post-Sampling Stratification10.3 Statistical Implications and Limitations
10.3.1 Transformation of Sample Observations
10.3.2 Confidence Limits for the Estimated Means
10.3.3 Allocation of Survey Samples
APPENDIX I. UNITS AND SYMBOLS
APPENDIX II. GLOSSARY OF TERMS
APPENDIX III. REFERENCES AND RECOMMENDED READING