NOAA Protocols for Fisheries Acoustics Surveys and Related ...

If individual targets do not appear in all quadrants, survey operations should be suspended
and the problem diagnosed.
Improvements
Improvements in monitoring system performance include continuous monitoring of the
output echo sounder power or voltage to the transducer. The ability to monitor voltage to the
transducer would provide real-time evaluation of the echo sounder performance.
Data Management
Documenting and archiving calibration data and supporting information is critical. In
addition to data and derived values acquired from the calibration software, data should be
collected directly from the echo sounder. Echo sounder data include high-resolution sample,
individual target strength, and volume scattering data. These data should be archived
immediately after conclusion of the calibration. Supporting information should be documented
and archived with the calibration data.
Calibration data, such as the data collected by the calibration software and the echo sounder,
and associated meta-data should be archived on-board upon completion of each calibration
exercise. These data are downloaded to shore-based computers and permanently archived for
each calibration.
Volume Backscattering Measurements (E i )
Data Collection
Definition & Importance
Volume backscattering (S v , m 2 /m 3 ) is the summation of echo energy (E i ) within a sampling
volume.
S v is a measure of the relative density of organisms and the primary measurement for
acoustically estimating fish densities and abundance. Equation 1 (Acoustical Background
section) details the dependency of S v on sound speed (c), acoustical frequency (f) and
wavelength (), pulse duration (), two-way integrated beam pattern (), S v gain (G 0 ), and
attenuation ().
Techniques
Echo Sounder Parameters
Scientific echo sounders allow the user to input the parameters: G 0 , c, , , and and to
choose the ping interval. The acoustic frequency (f) is defined by the echo sounder. Choosing
echo sounder settings should be done with the understanding of the interdependency of these
parameters and how they affect S v measurements (Furusawa, 1991).
The S v gain (G 0 ) is obtained from the echo sounder calibration (Calibration section). Choice
of the pulse duration () is dependent on the objectives and conditions of the survey. For higher
resolution of individual targets, a shorter pulse duration is desirable, whereas a longer pulse
duration is desirable for greater ranges because of a higher signal-to-noise (SNR) ratio. The echo
sounder must be calibrated at the pulse duration used during a survey. Sound speed (c) is
dependent on water temperature and salinity, so setting the sound speed requires a priori
knowledge of the environmental conditions expected during the survey. The two-way integrated
beam pattern () or beam width is defined by the transducer specifications supplied by the
manufacturer. Sound attenuation () and acoustic spreading combine for the total acoustical
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