NOAA Protocols for Fisheries Acoustics Surveys and Related ...

transmitted signal, however. The NWFSC does not apply a post-processing correction for
signal attenuation due to bubbles.
Transducer Motion – As with bubble attenuation, transducer motion is associated with vessel
motion, placement of the transducer, and sea state, thus many of the same considerations and
remediation methods apply. “Dropouts” on an echogram are a typical manifestation of
transducer motion. As with bubble attenuation, if transducer motions become excessive, vessel
speed or suspension of operations may be considered to preserve the quality of the data (see
Protocol 4, Sampling).
Bio-fouling – Bio-fouling refers to biological growth (e.g. barnacles) on the face of the
transducers. The effects of biofouling can be identified by unusual calibration results or
system performance measures (see Protocol 1, Calibration and System Performance).
Transducer faces should be inspected and cleaned if necessary before the beginning of a survey
or field season.
Error
Noise, bubble attenuation, excessive transducer motion, and biofouling will degrade system
performance and lower the signal to noise ratio of the data and any resulting biomass estimates.
Considerations
Remediation – If possible, the above sources of reduced performance should be avoided by
proper planning and setup, troubleshooting and elimination of noise problems encountered
during the survey, or post-cruise processing to remove or otherwise account for the problem, as
described in each section above. The error resulting from issues that reduce sounder
performance should be well understood.
Improvements – If applicable, motion sensor data may be used to correct acoustic
measurements.
Data Management
Acoustic Data
Raw data files and .ev files are logged, written to an external hard drive, and live viewed with
Echoview software. File size is limited to 10 MB to facilitate file handling and data transfer.
Raw data files are copied to a second external hard drive at the end of each transect or at the end
of a day’s operation to ensure that two shipboard copies of the raw data exist. This copy of the
raw data is judged with Echoview and saved on both external hard drives. Raw data, .ev files,
and judged data are burned to a DVD when enough data to fill the DVD (approximately 4.75
GB) have been accumulated. A total of three copies of the data are thus created.
Upon completion of the survey all data are uploaded to a server in the Seattle FRAM facility.
Duplicate DVD copies are archived to the Newport FRAM and Nanaimo DFO facilities such
that, overall, raw data from the survey reside in three separate physical locations.
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