A General Guide for Deriving Abundance Estimates from Hydroacoustic Data





















































Figures in order of occurrence

Click on figure number or caption to be transferred to the page containing the figure.

Figure 1. Schematic image of transducer beam pattern (scaled in dB and reproduced from Johannesson and Mitson (1983)). The full angle is the 3dB beam angle, which is defined as the angle between the lines that represent the half-intensity direction on either side of the main axis.

Figure 2.  Loss of acoustic signal strength (dB) due to absorption for common acoustic frequencies.

Figure 3. Expected TS of an alewife calculated using the Kirchhoff-Ray mode model at 70 kHz (left panel) and 120 kHz (right panel).  Details in Horne and Jech (2005).

Figure 4.  Variation in transducer size.  Top row (L to R): Simrad 38 kHz – 7o, 70 kHz – 11o , 120 kHz – 7o, 200 kHz - 7o, and 710 kHz - 6o.  Bottom row (L to R): Biosonics 120 kHz - 7o and 430 kHz - 6o.

Figure 5.  Frequency-dependent scattering.  Top five echograms are Sv data for 38, 120, 200, and 710 kHz Simrad EY60 and a 430 kHz Biosonics Dt-X units.  The two higher frequencies are single-beam units, the three lower are split-beam.  Data was collected while stationary in Cayuga Lake, New York in September 2006.  Most fish are alewife.  The backscattering below the thermocline (arrow) is from Mysis relicta.  All units except the 430 kHz were mounted on the same tow body.  The large fish below the thermocline is therefore not present on the 430 kHz.  Lower threshold in all top echograms are -80 dB.  Bottom depth is 86 m.  Noise has not been removed to illustrate the increase in noise levels at depth at higher frequencies.  Derived from Rudstam et al. (in prep).

Figure 6.  Transducer resolution and beam width.  Fish within a pulse volume (delineated with dashed lines) cannot be resolved separately.  More fish are within a pulse volume when the pulse duration is longer and when the beam is wider.  Reproduced from Brandt (1996) with permission from the American Fisheries Society. 

Figure 7.  Transducer configurations.  Single beam transducers give information on 1 dimension (depth), dual beam transducers gives information on 2 dimensions, depth and distance from the acoustics axis, and split beam transducers gives information on the location in all three dimensions. From Simrad educational material.

Figure 8.  Two towed body styles currently used in the Great Lakes.  The towed body on the left is 4’ long and the one on the right is 8’ long. 

Figure 9.  Photo of the Lake Erie pole mount.

Figure 10.  Sea Chest.  Schematic from Fleischer et al. (2002).

Figure 11.  Image of single rainbow smelt traces from stationary sounding.

Figure 12. Monofilament calibration sphere cradle tying instructions.  From Biosonics.

Figure 13.  Hull-mounted sphere deployment.  From Foote et al. (1987).

Figure 14. Simrad ER60 software showing the calibration sphere near the center of the acoustic axis. 

Figure 15.  Screen capture from the Simrad Lobes program, showing measurements of the calibration sphere in the beam.  The coverage of the beam would not be considered adequate in this instance.

Figure 16.  Example of an Excel spreadsheet for archiving calibration data over time.  An individual sheet should be created for each echosounder.

Figure 17.  Example parameter log for a two-frequency survey.

Figure 18. Minimum ping interval (s) as a function of depth.

Figure 19.  Effect of temperature on sound speed in freshwater.

Figure 20.  Echogram showing high noise detected at the surface and sharp fluctuations of the bottom (yellow line is the sounder-detected bottom).  The small inserts are an expansion of the surface and the bottom regions.

Figure 21.  Example datasheet for an acoustic survey. 

Figure 22.  Acoustic cross-talk (diagonal lines throughout the water column) between 70 kHz transducer and 50 kHz on-boat depth-sounder.

Figure 23.  Acoustic cross-talk between unsynchronized 70 kHz and 200 kHz survey echosounders.  Arrow indicates an echo return from side lobes hitting the survey vessel.

Figure 24.  Two examples of electrical interference seen on a 70 kHz echosounder.

Figure 25.  Improper towed body weighting, resulting in highly angled fish targets.  Also note the change in noise levels in the middle of the echogram.

Figure 26.  Passive data collected with 120 kHz echosounder, showing increases in noise with depth.  Lower threshold is -90 dB. 

Figure 27.  Noise produced during trawl deployment detected on 70 kHz echosounder.  Such noise may be manually classified as “bad” data or erased in post-processing programs, but underlying data are lost. 

Figure 28.  TS distribution from Onondaga Lake, May 2005, in water 2 to 10 m deep.  The three curves represent different angle standard deviations (0.6, 2, and 5) Analysis with EchoView method 1.  The shape of the distributions with method 2 is almost identical to method 1. With this distribution we consider -60 dB to be an appropriate minimum TS value to consider alewife, although -54dB may also be appropriate.  The lake was dominated by one age group of alewife (age 3 in 2005).

Figure 29.  Empirical data (squares) and theoretical variogram model (smoothed line) showing effective range of 3300 m.  In this example, a horizontal bin size of 250 m was selected. 500 to 1000 would also be appropriate.

Figure 30.  Vertical separation of young-of-year and yearling-and-older rainbow smelt in Lake Champlain.  Image taken from Parker Stetter et al. (2006).  

Figure 31.  Comparison of mobile survey (solid black), stationary survey (dashed black), and trawl capture (solid gray) estimates of TS for yearling-and-older rainbow smelt in Lake Champlain (young-of-year and yearling-and-older).  Noise threshold is shown as a vertical black line.  The “trawl” target strength is calculated from the trawl catch and a TS-L regression.  Taken from Parker Stetter et al. (2006).

Figure 32.  Alewife TS distribution from Onondaga Lake in spring 2005 dominated by one year class of alewife (age 3 – 150 mm, mean TS -42.8 dB) and from a large net cage (130 mm fish, mean TS -43.8 dB) at 70 kHz (summer 2005).  From Rudstam et al. (in press – fish tech chapter) 

Figure 33.  Decreasing Sv threshold over depth for a 120 kHz transducer with EBA of -20 dB, sound speed 1450 m•s-1 and pulse duration of 0.4 ms that correspond to a TSu threshold of -66 dB (see text).

Figure 34.  Empirical variogram data gathered on Sv using a 120 kHz echosounder averaged over the water column (<100 m deep) and fit with an exponential theoretical model with sill=5.04, effective range=3300 m, and nugget=2.90.  As distance increases between two points the variance of their difference, as denoted by the variogram, increases and then plateaus out at roughly the global or maximum variance value.  This global variance (or sill) minus the variogram estimate results in the perhaps more familiar correlation curve showing decreasing correlation with distance.