NOAA Protocols for Fisheries Acoustics Surveys and Related ...

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• Two-way integrated beam pattern (ψ) = -20.7 dB (supplied by Simrad; value is specific to individual 38 kHz transducers) • Absorption (α) = 10 dB/km • Sound speed (c) = 1480 m/s The sound speed and absorption settings are based on a compromise between previous AFSC survey sound speed settings and DFO Canada sound speed settings. All echo sounder parameter values are exported from the echo sounder to a text file (e.g., “EK500 settings”) daily during a survey as well as before and after a survey. Software –Acoustic data have been logged with SonarData EchoLog 500 (SonarData Pty Ltd, GPO Box 1387, Hobart TAS 7001, Australia) and in the future may be logged with SonarData Echolog60. Acoustic data are logged onto a PC and are backed up at the end of each transect. The echo sounder firmware version is recorded on the calibration sheets and is included in the daily export file of echo sounder parameters. The post-processing version used to analyze the data should be the most recent validated (non beta) version of SonarData Echoview. The post-processing version is included as a field in the Integration Settings table in the survey database. When upgrading versions, a reference set of data should be analyzed with both versions and the s A values (see definition of s A in Protocol 3) compared to ensure that no significant change has occurred to the echo integration algorithm. GPS – A GPS receiver(s) on the vessel sends navigation data to the echosounder where the data are logged with each ping. Mapping of the planned vessel route and recording of the actual vessel track are accomplished with a navigational software package (e.g. Seaplot or Simrad CM-60). Vessel speed and direction are also available with this software. Position data and vessel speed are monitored in real time. Oceanographic Data – Conductivity-temperature-depth (CTD) profiles may be conducted regularly during cruises, according to standard oceanographic procedures (Emery and Thomson, 1997) and relevant manufacturer guidelines. In general, these salinity and temperature profiles are not used to perform in-cruise updates of sound speed and sound absorption. Rather, single representative sound speed and absorption values are used for the entire survey. As sound speed and absorption may vary rapidly within a transect both in horizontal and vertical distance in the water column, updating sound speed based upon a local profile may generate more variability than it would reduce. Our survey values of 1480 m/s sound speed and 10 dB/km attenuation coefficient are a compromise between values obtained from DFO Canada and the AFSC historical oceanographic data. Detection Probability The NWFSC does not set a data collection S v threshold. The post-processing S v threshold is -58.5 or –69 dB, depending on the geographic area. Transects south of 47.3° N are analyzed with a threshold of -58.5, and those north of 47.3° N are analyzed with a threshold of -69 dB. This is based upon historical precedent from before the survey was transferred from the AFSC to the NWFSC. 112
The areas surveyed by the NWFSC range from shallow water through the shelf break to deeper water, covering depths from 1,000 m; see Protocol 1, Calibration and System Performance). Unusual noise levels can also indicate problems external to the system, such as noise from damaged propeller or an object entangled in the propeller (e.g., rope, kelp) or noise from other shipboard equipment (e.g., generators, compressors, other acoustic gear). Multiple scattering and shadowing The NWFSC has not observed the conditions that would indicate the need to correct for attenuation at high fish densities. Considerations Remediation – Under ideal circumstances, a volume backscattering threshold would not need to be used, as a threshold is a purposeful bias of the backscatter. This bias usually implemented to provide an improved signal to noise ratio, but can also have unintended consequences. Consideration should be given to the possibility that using a consistent threshold may not always yield consistent survey results. See also Protocol 4, Sampling. Improvements – Four new fisheries research vessels are currently being built for NOAA, one for each fisheries science center. The first will begin work for the AFSC in 2005. Each will meet ICES recommended noise standards (Mitson, 1995), reducing the potential for vessel noise to affect fish behavior and bias survey results. 113
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NOAA Protocols for Fisheries Acoust
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Echo Sounder Parameters ...........
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Trawls ............................
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Introduction In response to Vice Ad
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Advanced Survey Technologies Progra
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Techniques Before conducting a cali
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Considerations Remediation Echo sou
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transmission loss. To correct for s
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unavoidably discarded, just as some
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factors such as orientation are not
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A schedule for calibration and main
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Techniques Noise Acoustical A commo
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⎛ I ⎞ r TS ≡ 10 log10 ⎜ ⎟
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Considerations Remediation If a TS-
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Techniques Beam Pattern Transducers
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during vertical migration, will cau
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A schedule for calibration and main
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degradation are external to the ech
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permanently archived for each surve
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Numerical Density to Biomass Densit
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An electronic ‘event log’ can b
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References Demer, D.A., M.A. Soule,
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Regional Protocols Because of the d
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Table of Contents Introduction.....
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Electrical ........................
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Center Background NEFSC The Northea
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S v Calibrations The NEFSC acoustic
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Operation Menu/Transmit Power Norma
Page 62 and 63: Software The echo sounder firmware
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Page 66 and 67: Net mensuration sensors are attache
Page 68 and 69: We remove backscattering by surface
Page 70 and 71: GPS The primary Global Positioning
Page 72 and 73: Electrical Electrical noise protoco
Page 74 and 75: Scientific Computer System (SCS) Fi
Page 77: Appendix 2 March 11, 2005 NOAA Prot
Page 80 and 81: Techniques ........................
Page 82 and 83: Center Background AFSC The Alaska F
Page 84 and 85: On-axis sensitivity and S v calibra
Page 86 and 87: Volume Backscattering Measurements
Page 88 and 89: Mid-water juvenile pollock (max sa=
Page 90 and 91: Biological Sampling Mid-water and n
Page 92 and 93: Bubble Attenuation Vessel speed is
Page 94 and 95: Data Collection Since 1990 to the p
Page 96 and 97: sampling resolution of scattering l
Page 98 and 99: A decision must be made as to wheth
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Page 102 and 103: Simrad. 2001. Simrad EK60 scientifi
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Page 106 and 107: Acoustic Data......................
Page 108 and 109: ackscattering cross-section (σ i )
Page 110 and 111: o For the 38 kHz transducer operati
Page 114 and 115: Classification Techniques Single Fr
Page 116 and 117: Performance Degradation Definition
Page 118 and 119: Biological Data Data from catch pro
Page 120 and 121: elation also assumes that backscatt
Page 122 and 123: finer than the 13.5-18.9 nmi (25-35
Page 124 and 125: Improvements - The annual hake migr
Page 126 and 127: Techniques The primary source of th
Page 128 and 129: Hamano, A., Sasakura, T., Kieser, R
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