Fish Acoustics

Revised August 30th 2007

Acoustics Equipment: Fish biomass was estimated throughout the water column with a BioSonics DTX 120-kHz split-beam acoustics system (3 pings per second; 0.4 ms pulse length; -66 dB minimum acoustic backscatter threshold). Its transducer was towed 1 to 2 m below the surface, depending on sea state. Calibrations were conducted during every monthly cruise, using a 38-mm tungsten-carbide calibration sphere.

Data Processing: Acoustic backscatter data (bs) were integrated using Echoview (SonarData Inc., Hobart, Tasmania), and exported in 50 m x 1 m bins. We used bs as a relative measure of fish biomass density.

Variable Definitions

• Process ID: A number intended to be unique for each analysis export on any one PC, which can be used to identify, retrospectively, the exported files which originated from the same analysis.
• Interval: It reports the interval number of the cell being analyzed. Each interval consists of ~50 m, either longitudinally or latitudinally.
• Layer: It reports the layer number of the cell being analyzed. Each layer consists of 1 m depth.
• Sv_mean: It reports the mean Sv in the domain which was analyzed (dB re 1m-1).
• NASC: It reports the Nautical area scattering coefficient for the domain which was analyzed (m2/nmi2). Nautical area scattering coefficient is identical to sA as used by Simrad and is the area backscattering coefficient (ABC) scaled by 4? and 1 nautical mile squared. This terminology follows MacLennan and Fernandes (2000).
• Sv_max: It reports the maximum Sv in the domain which was analyzed (dB re 1m-1).
• Sv_min: It reports the minimum Sv in the domain which was analyzed (dB re 1m-1).
• Height_mean: It reports the mean height of the domain which was analyzed (m).
• Depth_mean: It reports the mean depth of the domain which was analyzed (m).
• Samples: It reports the number of good samples in the domain which was analyzed. That is samples which are not in a visible bad data region or have a value of no_data.
• Layer_depth_min: It reports the minimum depth of the cell (layer) which was analyzed (m). This is exported in depth mode only.
• Layer_depth_max: It reports the maximum depth of the cell (layer) which was analyzed (m). This is exported in depth mode only.
• Ping_S: It reports the number of the first ping in the domain which was analyzed (S for Start).
• Ping_E: It reports the number of the last ping in the domain which was analyzed (E for End).
• Ping_M: It reports the number of the middle ping in the domain which was analyzed (M for middle).
• Dist_S: It reports the distance (measured by GPS) from the first ping in the analyzed variable to the first ping in the domain which was analyzed (S for Start).
• Dist_E: It reports the distance (measured by GPS) from the first ping in the analyzed variable to the last ping in the domain which was analyzed (E for End).
• Dist_M: It reports the distance (measured by GPS) from the first ping in the analyzed variable to the middle ping in the domain which was analyzed (M for Middle).
• VL_start: It reports the distance (measured by vessel log) from the first ping in the analyzed variable to the first ping in the domain which was analyzed.
• VL_end: It reports the distance (measured by vessel log) from the first ping in the analyzed variable to the last ping in the domain which was analyzed.
• VL_mid: It reports the distance (measured by vessel log) from the first ping in the analyzed variable to the middle ping in the domain which was analyzed.
• Date_S: It reports the date of the first ping in the domain which was analyzed (S for start).
• Date_E: It reports the date of the last ping in the domain which was analyzed (E for end).
• Date_M: It reports the date of the middle ping in the domain which was analyzed (M for middle).
• Time_S: It reports the time of the first ping in the domain which was analyzed (S for start).
• Time_E: It reports the time of the last ping in the domain which was analyzed (E for end).
• Time_M: It reports the time of the middle ping in the domain which was analyzed (M for middle).
• Lat_S: It reports the latitude (in decimal degrees) of the first ping in the domain which was analyzed (S for start).
• Lat_E: It reports the latitude (in decimal degrees)of the last ping in the domain which was analyzed (E for end).
• Lat_M: It reports the latitude (in decimal degrees)of the middle ping in the domain which was analyzed (M for middle).
• Lon_S: It reports the longitude (in decimal degrees) of the first ping in the domain which was analyzed (S for start).
• Lon_E: It reports the longitude (in decimal degrees)of the last ping in the domain which was analyzed (E for end).
• Lon_M: It reports the longitude (in decimal degrees)of the middle ping in the domain which was analyzed (M for middle).
• Program_version: It reports the version number of Echoview used for this analysis.
• Processing_date: It reports the date on which this analysis was conducted.
• Processing_time: It reports the time at which this analysis was conducted.
• EV_filename: It reports the name of the EV file from which this analysis was conducted.
• Alpha: It reports the value of Absorption coefficient entered on the Calibration page of the Variable Properties dialog box for the variable which was analyzed (dB/m).
• ABC: It reports the Area backscattering coefficient for the domain which was analyzed (m2/nmi2).
• Area_Backscatter_Strength: It reports the Area Backscatter Strength for the domain which was analyzed (m2/nmi2). This is a logarithmic representation of ABC.
• Range_mean: It reports the mean range of the domain which was analyzed (m).

Investigator: Stuart A. Ludsin, NOAA-GLERL
Phone: 734-741-2355
Email:
Contact information after December. 1, 2007
Aquatic Ecology Laboratory, The Ohio State University
1314 Kinnear Road, Columbus, OH 43212
Phone: 614-292-1613
Email: