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Advanced Acoustical Modeling Tools for ESME

Advanced Acoustical Modeling Tools for ESME. Martin Siderius and Michael Porter Science Applications Int. Corp. 10260 Campus Point Dr., San Diego, CA sideriust@saic.com michael.b.porter@saic.com. Acoustic Modeling Goals.

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Advanced Acoustical Modeling Tools for ESME

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  1. Advanced Acoustical Modeling Tools for ESME Martin Siderius and Michael Porter Science Applications Int. Corp. 10260 Campus Point Dr., San Diego, CA sideriust@saic.com michael.b.porter@saic.com

  2. Acoustic Modeling Goals • Through modeling, try to duplicate sounds heard by marine mammals (e.g. SONAR, shipping) • Develop both high fidelity and very efficient simulation tools

  3. Difficult task for any single propagation code Approach is to use PE, Rays and Normal Modes Acoustic Modeling Goals • Accurate field predictions in 3 dimensions • Computational efficiency (i.e. fast run times) • Propagation ranges up to 200 km • R-D bathymetry/SSP/seabed with depths 0-5000 m • Frequency band 0-10 kHz (or higher) • Moving receiver platform • Arbitrary waveforms (broadband time-series) • Directional sources

  4. Model Comparisons Accuracy Rays NM and PE Computation Time Rays NM and PE Frequency Frequency

  5. Motivation

  6. Fast Coupled NM Method • Range dependent environment is treated as series of range independent sectors • Each sector has a set of normal modes • Modes are projected between sectors allowing for transfer of energy between modes (matrix multiply) • Algorithm marches through sectors • Speeds up in flat bathymetry areas • Pre-calculation of modes allows for gains in run-time (important for 3D calculation) • Very fast at lower frequencies and shallow water

  7. Mid Atlantic Bight: Example

  8. 5 dB more loss 5 dB less loss Mammal Risk Mitigation Map SD = 50 m SL = 230 dB Freq = 400 Hz Lat = 49.0oN Long = 61.0oW

  9. Shipping Simulator • Using the fast coupled normal-mode routine shipping noise can be simulated • This approach can rapidly produce snapshots of acoustic data (quasi-static approximation) • Self noise can also be simulated (i.e. on a towed array) • Together with a wind noise model this can predict the background ambient noise level

  10. Example: Simulated BTR • Input environment, array geometry (e.g. towed array hydrophone positions) and specify ship tracks (SL, ranges, bearings, time)

  11. Example: BTR from SWELLEX96

  12. Computing Time-Series Data for Moving Receiver • How is the impulse response interpolated between grid points? • How are these responses “stitched” together?

  13. 1. Interpolating the Impulse Response • In most cases the broad band impulse response cannot be simply interpolated • For example, take responses from 2 points at slightly different ranges:

  14. 2. “Stitching” the Responses Together • Even if the impulse response is calculated on a fine grid, there can be glitches in the time-series data (due to discrete grid points) • For example, take the received time-series data at points 1 m apart:

  15. Solution: Interpolate in Arrival Space • The arrival amplitudes and delays can be computed on a very course grid and since these are well behaved, they can be interpolated for positions in between. • Using the “exact” arrival amplitudes and delays at each point, the convolution with the source function is always smooth.

  16. Endpoint #2 Interpolated Endpoint #1 Advantage: very fast and broadband Ray/Beam Arrival Interpolation

  17. Test Case: Determine Long Time Series Over RD Track • Source frequency is 3500 Hz • Source depth is 7 m • Environment taken from ESME test case • Receiver depth is 7-100 m • Receiver is moving at 5 knots

  18. TL

  19. Received Time-Series

  20. Received Time-Series

  21. Received Time-Series (with Source Functions)

  22. Computing TL Variance • Fast Coupled Mode approach allows for: • TL computations in 3D (rapid enough to compute for several environments) • Changing source/receiver geometry • Ray arrivals interpolation allows for Monte-Carlo simulations of TL over thousands of bottom types to arrive at TL variance

  23. Endpoint #2 Interpolated Endpoint #1 Advantage: very fast and broadband Ray/Beam Arrival Interpolation

  24. Does it work? TL example • 100-m shallow water test case: • Source depth 40-m • Receiver depth 40-m • Downward refracting sound speed profile • 350 Hz • 3 parameters with uncertainty: • Sediment sound speed 1525-1625 m/s • Sediment attenuation 0.2-0.7 dB/l • Water depth 99-101 m

  25. Does it work? TL example • Interpolated (red) is about 100X faster than calculated (black)

  26. TL Variance

  27. TL Variance

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