Effect of the internal tide on mid- frequency transmission loss in - - PowerPoint PPT Presentation

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Effect of the internal tide on mid- frequency transmission loss in - - PowerPoint PPT Presentation

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Effect of the internal tide on mid- frequency transmission loss in the Shallow Water 2006 Experiment Jie Yang, Daniel Rouseff, Dajun Tang, and Frank S. Henyey (submitted to IEEE JOE SW06 special collections) Work supported by Office of Naval

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Effect of the internal tide on mid- frequency transmission loss in the Shallow Water 2006 Experiment

Jie Yang, Daniel Rouseff, Dajun Tang, and Frank S. Henyey

(submitted to IEEE JOE SW06 special collections)

Work supported by Office of Naval Research

Applied Physics Laboratory, University of Washington May 18 - 22, 2009 157th Meeting ASA, Portland, Oregon

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Goal

Model mean TL at mid frequencies under slowly time varying conditions due to the internal tide.

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Outline

  • Ocean data/modeling using multiple

mooring data for mid-frequency acoustic modeling.

  • Two acoustic data sets and corresponding

broadband PE simulation results:

  • 1. fixed range (550 m) data
  • 2. towed source data (max 8.1 km)
  • Summary and implications.
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4

Geometry for acoustic measurements and oceanographic moorings

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Sound speed recorded from mooring 54 for 18-19 August

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Acoustic data I: 550 m fixed range intensity, receiver depth 25 m, 1.5 – 6 kHz

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Group 1: direct + surface + direct Bottom bounc e Bottom

  • surface

Surfac e- bottom

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Group 1: direct + surface + direct Bottom bounc e Bottom

  • surface

Surfac e- bottom Phase 1: 3 arrivals in group 1 well separated, arrival time relatively stable

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Group 1: direct + surface + direct Bottom bounc e Bottom

  • surface

Surfac e- bottom Phase 2: group 1 getting more compact; earliest arrival time shifts toward bottom bounce. Phase 1: 3 arrivals in group 1 well separated, arrival time relatively stable

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Group 1: direct + surface + direct Bottom bounc e Bottom

  • surface

Surfac e- bottom Phase 3: group 1 widens as thermocline being depressed before the nonlinear internal wave

NLIW Rouseff et al., JASA-EL

Phase 1: 3 arrivals in group 1 well separated, arrival time relatively stable Phase 2: group 1 getting more compact; earliest arrival time shifts toward bottom bounce.

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Simulation strategy

  • Goal: develop a range-independent

acoustic model to simulate observed arrival structure.

  • Approach: broadband Parabolic Equation

simulation.

  • Example: Fourier synthesis of PE runs in

1.5 - 6 kHz with pulse length 400 ms using a CTD profile from the KNORR.

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Acoustic data versus broadband PE simulation

(CTD input, receiver depth 25 m, 1.5 – 6 kHz)

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Acoustic data versus broadband PE simulations (cont’d)

White: mooring data; magenta: CTD. (Receiver depth 25 m, 1.5 – 6 kHz)

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15 16 17 18 19 20 21 22 23

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2 4 6 Time (hour) Intensity (dB) Raw data Low-pass filtered data PE simulation

Data/model comparison of acoustic intensity of the first arrival group

Receiver depth 25 m, 1.5 – 6 kHz

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SLIDE 15

15 16 17 18 19 20 21 22 23

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2 4 6 Time (hour) Intensity (dB) Raw data Low-pass filtered data PE simulation

Intensity increases between 16 to 19 hours 20-21 hour, poor agreement when the wave passes Overall of 5 dB intensity change before/after the wave

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Geometry for acoustic measurements and oceanographic moorings

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Acoustic data II: towed source data at receiver depth 25 m, 1.5 – 6 kHz

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500 1000 1500 2000 2500 3000 10 20 30 40 50 60 70 80 Depth (m) Range (m)

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  • 10

10 20 0.5 1 1.5 2 2.5 3 Reduced time (ms) Range (km) Launch angle upward Launch angle downward

500 1000 1500 2000 2500 3000 10 20 30 40 50 60 70 80 Depth (m) Range (m)

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SLIDE 19
  • 20
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10 20 0.5 1 1.5 2 2.5 3 Reduced time (ms) Range (km) Launch angle upward Launch angle downward

500 1000 1500 2000 2500 3000 10 20 30 40 50 60 70 80 Range (m) Depth (m) 500 1000 1500 2000 2500 3000 10 20 30 40 50 60 70 80 Range (m) Depth (m)

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Reduced transmission loss at receiver depth 25 m with 1 kHz bandwidth

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Modeling strategy

roadband PE simulations se Mooring 54 for SSPs. reak 8.5 h data into 27 20-min windows. verage SSP over the window. esult: range-independent, slowly varying

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1490 1500 1510 1520 1530 1500 1510 1520 1530 1500 1510 1520 1530 1500 1510 1520 1530 1500 1510 1520 1530 10 20 30 40 50 60 70 80 Sound speed (m/s) Depth (m)

Mean SSP 1 00:30 0.1 km Mean SSP 7 02:30 1.8 km Mean SSP 13 04:30 3.8 km Mean SSP 19 06:30 5.7 km Mean SSP 25 08:30 7.5 km

Progress of sound speed profiles using Mooring 54 over 8 h period

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Data/model comparison of reduced transmission loss

receiver depth 25 m, 2.5 kHz ± 1 kHz bandwidth

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Summary Acoustic Data and Modeling

Acoustical effects of the rising thermocline:

  • 1. 550 m data: changing arrival pattern and 5 dB change in

acoustic intensity.

  • 2. Towed source data: 2 dB change in acoustic intensity.

Broadband PE together with range- independent / slow time-varying ocean model captures gross characteristics of TL.

  • 1. At 550 m, good model/data agreement for both intensity and

arrival pattern.

  • 2. For towed source, overall good agreement.
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Implications

  • Acoustical effects of the rising thermocline are

significant, observable, and predictable.

  • Nearby mooring data improve acoustic modeling.
  • The observed acoustic variations due to the internal

tide impacts geoacoustic inversion.