NOAA Protocols for Fisheries Acoustics Surveys and Related ...

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On-axis sensitivity and S v calibration Using the echo sounder display of the target in the acoustic beam, the operator moves the sphere to the acoustic axis. On-axis measurements of sphere TS (compared to the standard sphere’s known TS) are used to estimate the system’s TS gain parameter. On-axis measurements of the sphere S A (compared to the theoretical S A ) are used to estimate the system’s Sv gain parameter. (Note: EK500 defines both TS gain and Sv gain; EK60 uses the terminology TS gain and SA correction, where Sv gain = TS gain + SA correction.) With the sphere unmoving and few scatterers near the sphere, approximately 10 minutes of data collection are sufficient to provide a reasonable sample size for this purpose. Echoview software is used to process these data for estimates of sphere TS and sphere S A . Estimates of TS gain and Sv gain are required for each frequency-power-pulse length-bandwidth combination to be used during the survey. Beam pattern measurements For the two-way integrated beam pattern parameter, AFSC uses the nominal value supplied by Simrad upon delivery of the transducer. The Lobe software program provides a means to check for significant changes to this value. With the remote control downrigger system, the operator swings the sphere through the acoustic beam filling in a circle of data points centered on the acoustic axis. A model of the beam pattern is then fit to these data, providing estimates of TS gain, 3dB beam width and offset angles. TS gain as estimated from this model fit is used as a further check of the on-axis derived value. Results reveal that these two estimates of TS gain differ by no more than 0.1 dB for our 38 kHz EK500 system. Long-term averages of the measured beam width and offset angles are used in the acoustic system for collection and processing of TS data. Oceanographic data A fixed sound speed of 1470 m/sec is used for calibration (and survey data collection) of the EK500. For the 38 kHz EK500 system, a fixed attenuation coefficient of 10 dB/km is used for calibration (and survey data collection). For calibration (and survey data collection) with the 120 kHz EK500 system, the attenuation coefficient is set to 38 dB/km in the summer field season and 29 dB/km in the winter field season. These fixed values of sound speed and attenuation coefficient were derived from averages of historical oceanographic data from the survey regions. A CTD is deployed at the calibration site to provide a temperature-salinity-depth profile. For calibration of the EK60, the temperature-salinity-depth profile data are used to provide an averaged value for sound speed and attenuation coefficient between the transducer and the appropriate sphere. Update guidelines For the 38 kHz EK500 system, AFSC uses a slightly different set of gain parameters for the summer and winter field season. This system has demonstrated remarkable stability through time and for a wide range of environmental conditions. Gain estimates have not varied more than 0.2 dB from the current system values (Fig. 1). Gain estimates for the 120 kHz EK500 system are much less stable and system parameters are assigned on a survey-by-survey basis. 84
26.3 26.2 26.1 Winter Winter System Value Summer Summer System Value 26.0 25.9 TSgain 25.8 25.7 25.6 25.5 25.4 25.3 5-Mar-99 21-Sep-99 8-Apr-00 25-Oct-00 13-May-01 29-Nov-01 17-Jun-02 3-Jan-03 Date Figure 1. Winter and summer TS gain measurements from calibration of the AFSC 38 kHz Simrad EK500 system. System Performance Further details about AFSC system performance checks can be found in the following operating manuals - MACE (2003a), Simrad (1997), and Simrad (2001). To ensure system stability, the following checks are conducted daily. A snapshot of system parameters is recorded to a file. With the transmitter disabled, the internal test oscillator amplitude is confirmed to be within specification. With the transmitter enabled and the aid of an oscilloscope, transmit current for each of the four transducer quadrants is checked for any significant change. Should a problem exist, these two checks can help isolate the offending component. If both the test tone and current are bad, it is most likely the transducer. If the test tone is bad and the current is good, it is most likely the receiver. If the test tone is good and the current is bad, it is most likely the transmitter (Dan Twohig, pers. comm.). 85
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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
Page 34 and 35: during vertical migration, will cau
Page 36 and 37: A schedule for calibration and main
Page 38 and 39: degradation are external to the ech
Page 40 and 41: permanently archived for each surve
Page 42 and 43: Numerical Density to Biomass Densit
Page 44 and 45: An electronic ‘event log’ can b
Page 46 and 47: References Demer, D.A., M.A. Soule,
Page 48 and 49: Regional Protocols Because of the d
Page 51 and 52: Table of Contents Introduction.....
Page 53: Electrical ........................
Page 56 and 57: Center Background NEFSC The Northea
Page 58 and 59: S v Calibrations The NEFSC acoustic
Page 60 and 61: Operation Menu/Transmit Power Norma
Page 62 and 63: Software The echo sounder firmware
Page 64 and 65: ii. Minimum Sv for good pick: -50.0
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 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
Page 100 and 101: design. If fish abundance in this a
Page 102 and 103: Simrad. 2001. Simrad EK60 scientifi
Page 104 and 105: 104
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 112 and 113: • Two-way integrated beam pattern
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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