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The Pathway A program for regulatory certainty for instream tidal energy projects Presentation Scientific Echosounder Review for In-Stream Tidal Turbines Principle Investigators Dr. John Horne August 2019 Scientific-grade echosounders are a standard tool in fisheries science and have been used for monitoring the interactions of fish with tidal energy turbines in various high flow environments around the world. Some of the physical features of the Minas Passage present unique challenges in using echosounders for monitoring in this environment (e.g., entrained air and suspended sediment in the water column), but have helped to identify hydroacoustic technologies that are better suited than others for achieving monitoring goals. John Horne’s report and presentation will present a overview of echosounders and associated software that are currently available for monitoring fish in high-flow environments, and identify those that are prime candidates for monitoring tidal energy turbines in the Minas Passage. This project is part of “The Pathway Program” – a joint initiative between the Offshore Energy Research Association of Nova Scotia (OERA) and the Fundy Ocean Research Center for Energy (FORCE) to establish a suite of environmental monitoring technologies that provide regulatory certainty for tidal energy development in Nova Scotia.
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John K. Horne University of Washington
Open Hydro
Echosounder Review for Fish Monitoring Around Tidal Turbines Listening in the Noise
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Typical Acoustic Targets Mid-water Layers
Bottom aggregations Demersal, Single Targets
Mid-water, Single Targets
Echo Counting
Echo Integration
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Photo credit: L. McGarry
Using Sound as a Sensor:
How to detect swimbladdered fish in bubbly, turbulent water?
WOW THAT IS SOME SERIOUS RIP
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What is an Echo? An acoustic impedance mismatch resulting in a reflection
Acoustic Impedance (Z) Z = density x sound speed = ρ c
g = ρ2/ρ1 h = c2/c1
density contrast sound speed contrast
11
1
1
11
22
11
22
1122
1122
+−
=+
−=
+−
=ghgh
cccc
ccccR
ρρρρ
ρρρρAnything with a density different than
water will reflect sound
Comparing Impedance at an Interface
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Echo Amplitudes f(Frequency)
Holliday and Pieper 1980
Rayleigh Resonance Geometric or Specular
Lavery et al. 2002
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Bubble TS: Model Estimate
Courtesy of T. Ryan
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Courtesy of T. Ryan
TS of 0.06 mm bubble (width of human hair) at 120 kHz ≈-64 dB
If 254 bubbles ensonified then backscatter ≈ -40 dB
Bubble Ensemble
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Fish Target Strengths Walleye pollock (Gadus chalcogrammus)
Length (mm)100 200 300 400 500 600
Targ
et S
treng
th (d
B)
-50
-45
-40
-35
-30
-25
TS=20log(L)-66
38 kHz n= 48 fish
120 kHz
comparison of backscatter to statistical model
Backscatter Model Visualization
Horne 2003
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Needed Sensor Characteristics General Calibratable: accuracy and precision of measurements Constant source level and TVG: accuracy and precision of measurements Known beam pattern: accuracy and precision of measurements Digital output: data processing and analysis
MRE Maximize SNR: CHIRP signal + matched filter for target detection Physical footprint and packaging: ‘fit’ in deployment platform Power and communications: ‘fit’ with deployment strategy and sample design
Data Processing compatible with commercial processing software for bulk processing (Echoview, LSSS, SonarX)
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What Determines Echo Amplitude?
Simplified Sonar Equation
Echo Amplitude = Source Level + Target Echo + Beam Compensation – Transmission Loss
EL = SL + TS + 2Di(φ,θ) - (40log(r) + 2αr) Source Level
Target Strength
Beam Directivity
Spreading Absorption Echo Level
How to Increase Echo Amplitude (relative to noise)? 1. Increase source level (amplifies everything) 2. Reduce distance to targets (strategic deployments) 3. Increase signal-to-noise ratio (increase signal (see 1), reduce noise, change
pulse type) 4. Match transmit frequency to target resonance peak (lower transmit
frequency but operational and regulatory constraints) 5. Process data to remove noise (ambient noise filter, mask unwanted targets)
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Transmit Pulse Types Narrowband
Broadband Frequency Modulated (FM) Linear up-sweep (CHIRP)
Continuous Wave (CW)
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Broadband Matched Filtering
Transmit Pulse
Time –dependent Frequency
Receive Echo Delay
Receive Echo Amplitude
Ehrenberg & Torkelson 2000
Stanton 2010
SNR increase ~ 15 dB over CW pulse (depends on pulse bandwidth)
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Commercial, Scientific Echosounders Tier I: calibrated, internationally vetted, digital output
Simrad EK80 HTI Model 244 BioSonics DTX Extreme
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Commercial, Scientific Echosounders Tier II: calibratable, consistent TVG, international vetting underway
ASL AZFP Nortek Signature 100
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Commercial, Scientific Echosounders Tier III: not internationally vetted
Furuno FQ80 Imagenix 853 Kaijo/Sonic KFC-3000