NOAA Protocols for Fisheries Acoustics Surveys and Related ...

Considerations
Remediation
If a TS-length regression is found to be incorrect or numerical and analytical model
predictions are found to be erroneous, and these results were incorporated in survey estimates,
then analyses must be performed to determine the effect of these errors in population estimates.
Improvements
Significant effort improving and verifying target strength predictions by numerical and
analytical models is required. Improved understanding and characterization of target strength
relative to organism size and behavior is required. Even if TS measurements are not directly
used in survey estimates, target strengths can be useful for evaluating changes in S v .
Data Collection
Definition & Importance
Target strength data collection is the operational procedures used to acoustically resolve
individuals.
Target strength is an important scalar for converting S v measurements to absolute values.
Organisms must be acoustically resolvable for valid target strength measurements. Acoustic
resolution is defined as the ability to separate echoes among individuals and is based on the pulse
duration () and sound speed (c):
cτ
R
2
− R1
>
(6)
2
where the R’s are the ranges for two targets (subscript 1 and 2) (MacLennan and Simmonds,
1992).
Techniques
Echo sounder Parameters
A generic method to separate echoes by individuals involves selecting peak amplitudes above
a threshold, measuring the echo width (either time- or range-based), and comparing the echo
width to the pulse duration. Different echo sounder manufacturers apply this single target
detection method differently. It is important to understand the specific method the echo sounder
uses and the parameter settings employed.
Software
As with echo sounder manufacturers, different post-processing software packages apply
single target detection algorithms differently. It is important to understand the specific method
and parameters used by post-processing software, and to document the algorithms, parameters,
and software versions.
In situ data
Collecting in situ target strength data should be a routine operation during surveys and is as
important as collecting biological data regardless of the ultimate use of target strength data in
survey estimates. Target strength data can be collected while transecting and/or at selected sites.
Numbers, locations, and timing of target strength operations are dependent on the objectives of
the survey.
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