Resonance classification of swimbladder-bearing fish using broadband acoustics: 1-6 khz

Transcription

1 Resonance classification of swimbladder-bearing fish using broadband acoustics: 1-6 khz Tim Stanton The team: WHOI Dezhang Chu Josh Eaton Brian Guest Cindy Sellers Tim Stanton NOAA/NEFSC Mike Jech Francene Stroman NRL Joe Fialkowski Roger Gauss Ed Kunz Richard Menis NPS Ben Jones Independent Aija Irene Briga A.C. Hill

2 Interpreting acoustic data in terms of meaningful biological quantities Echogram Echo Voltage Scattering models Length, type, Numerical density, Spatial/temporal distribution

3 Resonance classification using broadband acoustics Swimbladder Resonance One Fish Broadband Scattering dominated by swimbladder, which resonates at low frequencies Narrowband Depth Resonance depends on: Fish size and depth Mixed assemblage

4 Types of acoustic signals: Narrowband gated sine wave Broadband Impulse Linear frequency modulation chirp!! time frequency

5 Pulse Compression Processing Method: Cross correlate broadband echo with replica (similar to matched filter processing) Result: Short signal, duration = (bandwidth) -1 Improved resolution and SNR through processing

6 Advantages of broadband signal over narrowband signal 1. Broad spectrum provides more information (for classification of marine organisms) Through signal processing, one can achieve: 2. Higher range resolution 3. Higher signal-to-noise ratio

7 Ocean experiment two mid-frequency systems ~3 kts Horizontal-looking ( khz (NRL) HLA mode < ~ 10 km) Broadband signals time frequency Down-looking ( < ~ 200 m) khz (WHOI)

8 Area of study

9 WHOI down-looking, modified-echosounder system 4-Channel System 1-6 khz 4-20 khz khz khz Calibration: at sea Standard target (sphere) Eliminated sphere resonances Stanton/Chu JASA (2008)

10 Pelagic trawl FR/V Delaware II Atlantic herring

11 Net samples all combined 2008 Atlantic herring Red fish Number of fish Silver hake Butterfish Pearlsides Red hake Length (cm) Squid

12 Traditional system (120 khz narrowband) New system (lower frequency, broadband) Improved resolution: Broad bandwidth, matched filter processing and flying low Reduced ambiguity: Lower frequency naturally selects only swimbladder-bearing fish Stanton/Chu/Jech/Irish ICES JMS (2010)

13 Traditional system (120 khz narrowband) New system (lower frequency, broadband) Improved resolution: Broad bandwidth, matched filter processing and flying low Reduced ambiguity: Lower frequency naturally selects only swimbladder-bearing fish Stanton/Chu/Jech/Irish ICES JMS (2010)

14 Resonance Classification Resonance (3.7 khz) Atlantic Herring Dense Patch (0.3 m -3 ) Sparse Patch (0.05 m -3 ) Observations: Strong echo (upper) and weak echo (lower) have same resonance freq. Reduced ambiguities: Difference in echo strength is due to difference in density of fish, not size of fish or its orientation distribution Stanton/Chu/Jech/Irish ICES JMS (2010)

15 Mixed assemblages of fish Silver Hake Herring 25 cm Herring 25 cm Mix of fish 2-5 cm Stanton/Sellers/Jech CJFAS (2012)

16 Resonance classification of mixed assemblages Aggregation J Aggregation E Depth (m) Lower resonance Lower resonance Larger fish Higher resonance Higher resonance Smaller fish Distance (km) Distance (km) Stanton/Sellers/Jech CJFAS (2012)

17 NRL horizontal-looking long-range system RECEIVER SOURCE HLA and VLA configurations 32 elements cut for 5 khz Vertical Line Array (VLA) cut for 3 khz Frequency: khz 10 transducers Towable at up to 4 kts 2 sensor suites (depth, tilt, etc.) ~Omni azimuthally Source level (SL) best: ~3.5-9 khz Waveforms and Down-range resolutions khz LFM: khz LFM: khz LFM: 0.77 m 0.17 m 0.10 m

18 50 50 Predictions sourc receiver e Data Fish ensonified in 1 st two annuli m/s non-herring: 30 m above seafloor km herring: m 65 Fish ensonified in deep shadow zone? Or shallow refracted path? Fish ensonified in third annulus 18

19 Observed Echo Spectra Observed Spectra (db) 48 Set A redfish N echoes = redfish herring Set B N echoes = Modeled VSS (db) Observed Spectra (db) 48 redfish herring Set C -32 N echoes = frequency (khz) 40 redfish herring Set D -32 N echoes = frequency (khz) Modeled VSS (db) Jones (2012) and Jones et al. (in manuscript) 19

20 Summary Range resolution: Improved through broadband processing Signal-to-noise ratio: Improved through broadband processing Ambiguities: Reduced through resonance/spectral classification, use of low frequencies Multiple size classes: Can spectrally resolve different sizes of fish with broadband sound that cannot be spatially resolved Long-range sonar: Can classify fish through their resonances, discriminate from seafloor and sea surface echoes

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22 Backup

23 Papers on resonance classification and broadband calibration Stanton, T.K. and D. Chu (2008), Calibration of broadband active systems using a single standard spherical target, J. Acoust. Soc. Am., 124, Stanton, T.K., D. Chu, J.M. Jech, and J.D. Irish (2010), New broadband methods for resonance classification and high-resolution imagery of fish with swimbladders using a modified commercial broadband echosounder, ICES J. Mar. Sci., 67: Stanton, T.K., C. Sellers, and J.M. Jech (2012), Resonance classification of mixed assemblages of fish with swimbladders using a broadband echosounder at 1-6 khz. Can. J. Fish. Aq. Sci., 69: Jones, B.A., T.K. Stanton, J.A. Colosi, R.C. Gauss, J.M. Fialkowski, and J.M. Jech (in manuscript), Broadband classification and statistics of long-range mid-frequency sonar measurements of aggregations of fish, to be submitted to J. Acoust. Soc. Am. (based on Jones 2012 thesis)

24 Calibration of broadband active acoustic systems using a single standard spherical target Stanton and Chu (2008), JASA

25 Standard target calibration System response transducer calibration sphere Approach: Normalize measured target response with predicted response Issue: Resonances in scattering response of target can cause error

26 Source of resonances (shell or solid) Interference in total echo: f FI f (front + c (circumferential interface) waves) + internal waves New approach: use signal processing to isolate f FI completely eliminates resonances

27 Scattering Amplitude (normalized) Partial Wave Analysis Frequency (khz) ka Standard method: full wave New method: partial wave Impulse Response Analyze echo from front interface only Time (µs)

28 Largest Calibration Sphere air-filled shell water-filled shell

29 At Sea Experiment

30 Results Full wave: contains resonances Partial wave: no resonances Based on partial wave

31 Target strength, Sonar equation (resolved targets):

32 Volume scattering strength, Sonar equation (resolved/unresolved targets in volume V):

33 Net samples Night, upper water column 2008 Atlantic herring Red fish Number of fish Silver hake Butterfish Pearlsides Red hake Length (cm) Squid

34 Net samples night, lower water column 2008 Atlantic herring Red fish Number of fish Silver hake Butterfish Pearlsides Red hake Squid Length (cm)

35 Net samples day, upper water column Atlantic herring 2008 Red fish Number of fish Silver hake Butterfish Pearlsides Red hake Length (cm) Squid

36 Net samples day, lower water column Atlantic herring 2008 Red fish Number of fish Silver hake Butterfish Pearlsides Red hake Length (cm) Squid