Modeling Impulsive Sources in the Context of ESME

Transcription

1 Modeling Impulsive Sources in the Context of ESME James H. Miller and Gopu R. Potty University of Rhode Island Department of Ocean Engineering Narragansett, RI phone: (401) fax: (401) Award Number: N LONG-TERM GOALS Our long-term objective is to support the ESME program by; 1. Maintaining and updating the database of sediment and bottom properties including sediment compressional wave speed, shear wave speed, attenuation and density. 2. Developing simple source models to predict the acoustic field at short ranges due to impulsive sources (explosive sources, air guns etc.). 3. Participating in the review of different versions of the ESME software. OBJECTIVES Our objectives: To update the sediment geoacoustic models for the U.S coastal waters. Progress has been made in the last years in regard and we would like to continue this effort and make the model more useful to ESME and the acoustic community in general. Develop a simple MATLAB code to model the acoustic field at short ranges due to explosive sources. We have already implemented explosive source models in the ESME module. APPROACH We have been part of the ESME initiative since its beginning and we have developed sediment models for the U.S East Coast and other test regions. These models were based on published data (gravity/piston/vibro cores, seismic surveys, deep cores, grab samples and inversions) and sediment databases. The sediment databases (USGS sediment texture database and NGDC grain size and sediment texture databases) provided sediment physical property information with very good spatial coverage. These sediment property data provided inputs to a geoacoustic model (Biot-Stoll or Buckingham model) in order to estimate geoacoustic parameters (compressional wave speed, shear wave speed, attenuation etc.). The geoacoustic parameters thus obtained were tuned to a specific location using an approach developed based on matching the predictions with available good quality 1

2 data. Our continuing objective is to augment the current version of sediment model with new measurements and inversions as and when they become available. Another goal was to develop a simple MATLAB code to model the acoustic field at short ranges due to explosive sources. Acoustic field thus produced can be then input to a PE code as starting field for long range propagation modeling. Matlab codes to calculate the source parameters were developed as part of this effort and were successfully incorporated in the ESME model. Our current interest in this area is to modify the explosive source model so that it can be applied to different scenarios (surface explosions, explosions on land near water etc.). WORK COMPLETED As part of the ESME program we have developed sediment geoacoustic models for different locations. These models are now part of the ESME module. These models were based on published data (gravity/piston/vibro cores, seismic surveys, deep cores, grab samples and inversions) and sediment databases. The sediment databases (USGS sediment texture database and NGDC grain size and sediment texture databases) provided sediment physical property information with very good spatial coverage. These sediment property data provided inputs to a geoacoustic model (Biot-Stoll or Buckingham model) in order to estimate geoacoustic parameters (compressional wave speed, shear wave speed, attenuation etc.). The geoacoustic parameters thus obtained were tuned to a specific location using an approach developed based on matching the predictions with available good quality data. Figure 1. Sediment inversion using Combustive Sound Source (CSS). The estimated compressional wave profile is shown on the left along with acoustic signal from CSS (top panel on the right) and the dispersion based short-time Fourier transform (bottom panel on the right). The continuous lines on the time-frequency diagram are the modal arrival times calculated for the estimated compressional wave speed. 2

3 The Matlab codes to calculate the source parameters for explosive waveforms are now part of the ESME model. We have used an approach in which the shockwave peak pressure and two bubble pulses is computed using various empirical relations. The source spectrum can be used in combination with the existing propagation models in ESME to compute the field at any location. The energy levels computed using the ESME Matlab code compares well with the published values for a.82 kg charge at 99.6 m (Chapman1). RESULTS The sediment model developed for the ESME program will be updated with new data in the form of direct measurements (sediment cores) and inversions based on acoustic data. New data include measurements taken during the SW-06 experiments. Direct measurements and inversions using acoustic data is expected out this experiment. We have made some inversions using data from the Combustive Sound Sources (CSS) which were deployed by ARL- UT group. Data from these CSS collected on the WHOI HLA/VLA were used to invert for the compressional wave speeds of the sediments. The inversions were carried out using our modal dispersion based long range sediment tomography technique2. Figure 2 shows the CSS data, the modal arrivals and the compressional wave speeds calculated using the modal arrivals. Preston Wilson (ARL-UT), James Lynch and Arthur Newhall (WHOI) were collaborators in this study. Figure 2. Acoustic signals collected near the mouth of the Eagle River in the Knik Arm of Cook Inlet, Alaska. The explosion that produced this signal was in land adjacent to the river. The ESME explosive source model can calculate the source levels for explosives detonated within the water-column. We are planning to augment the capabilities of the model by looking at scenarios where explosive charges detonate at the water surface or near the water in ground (transfer of explosive shock wave from ground to water). 3

4 Figure 3. Comparison of acoustic sound levels at distances 28.2, 30.3 and 34.7 km from source to receiver. The three plots on the right show the spectrograms at these ranges. The sound pressure level plot has been demodulated and low-pass fltered in relation to the 93 Hz source signal. Notice the 93 Hz band present in the spectrogram at 28.2 km, which disappears at 30.3 km and reappears at 34.7 km. The top panel on the left show the acoustic signal at 93 Hz at these three ranges showing fluctuations of the order of 5 to 6 db. Bottom panel on the left shows 3D KRAKEN results of acoustic modal rays reflecting of a shelf break front and non-linear internal wave packet. The source is at (5km, 0) Recently we took measurements in water and collected acoustic data from explosive charges detonated on land near water3. These field measurements were conducted near the mouth of the Eagle River in the Knik Arm of Cook Inlet which is the habitat for a distinct population of beluga whales. Figure 2 shows an example of the data collected during this study. The upper panel in that figure shows the time series of the acoustic signal transferred through ground while the lower panel shows the spectrogram. These data could be used to calibrate the models for predicting transfer of acoustic energy into water from shockwaves originating in ground. There are some empirical models available4 to model the propagation of shock waves through the ground into the water and thereafter and the data collected will be useful in calibrating any such model. This modeling work is ongoing. Horizontal Lloyd s mirror was one of the effects considered by Lynch et al5. which could have some effect on the ESME acoustic exposure model. A potential 6 db increase in maximum ensonification 4

5 level, along with deep nulls, is certainly a nonnegligible perturbation to the acoustic field. We are now analyzing the data from the SW-06 experiment to further explore this effect. Signals were recorded on the WHOI-VLA/HLA from a ship-towed J15 source, using a simple CW tone at 93 Hz and a source depth of approximately 50 meters. The J-15 was towed for a distance of 60 km parallel to the shelf break front, which was located at the 110 m isobath that day, based on scanfsh measurements. Figure 2 shows some preliminary results showing the fluctuations in received acoustic levels of the order of 5 to 6 db. Modeling also predicts possibility for fluctuations of these magnitudes. Modeling the 3-D propagation effect was done using the horizontal ray-vertical modes approach (3-D version of Kraken). Figure 2 shows the acoustic field received at the WHOI Shark HLA-VLA at three ranges 28.2 km, 30.3 km and 34.7 km. We can see a 5 to 6 db increase in the levels between 34.3 km and 30.3 km. Future work planned We plan to be involved in the ESME team by modifying and updating the sediment database and source models and attending any future meetings or workshops. IMPACT/APPLICATIONS Our effort is intended to provide the best possible estimates of sediment data needed for the propagation modeling component of the ESME initiative. This will enable the propagation modelers to use best guesses when direct estimates of the sediment data is not readily available. TRANSITIONS We expect that this sediment model, when complete, will be useful to the acoustic community as a whole as an important database of sediment property information. RELATED PROJECTS We are currently analyzing the data collected during the SW-06 experiment to understand the effects of 3-D acoustic propagation and for sediment inversions. REFERENCES 1. Chapman, N. R., Measurement of the waveform parameters of shallow explosive charges, J. Acoust. Soc. Am., 78(2), Potty, G., Miller, J.H., Lynch, J.F., and Smith, K.B. (2000). Tomographic mapping of sediments in shallow water," J. Acoust. Soc. Am., 108(3), P. M. Scheifele, S. Tremblay, J. H. Miller and G. R. Potty, Acoustic measurements in the Eagle Bay, Alaska- Preliminary Report, Report submitted to U.S Army Cold Regions Research and Engineering Laboratory (CREL), (2007). 4. P. D. Smith and J. G. Hetherington, Blast and Ballistic Loading of Strictures, Butterworth, New York,

6 5. James F. Lynch, John A. Colosi, Glen G. Gawarkiewicz, Timothy F. Duda, Allan Pierce, Mohsen Badiey, Boris Katsnelson, James H. Miller, William Siegmann, Ching-Sang Chiu and Arthur Newhall, Consideration of fine scale coastal oceanography and 3-D acoustics effects for the ESME sound exposure model, Oceanic Engineering, IEEE Journal of, Volume 31, Issue 1, 33 48, (2006) REFEREED PUBLICATIONS 1. Potty, G and Miller, J. H., Dispersion of broadband acoustic normal modes in the context of long range sediment tomography,, in Acoustic Inversion Methods and Experiments for assessment of Shallow Water Environment, Chapman, Caiti, Hermand. eds., Springer, 57-72, (2006). 2. Knobles D. P., Yudichak, T. W., Koch R. A., Cable P. G., Miller J. H., Potty, G. R., Inferences on seabed acoustics in the East China Sea from distributed acoustic measurements, IEEE J. Oceanic. Eng., 31(1), , Zoi- Heleni Michalopoulou, Miller, J. H., and Potty, G. R., Matched field inversion in the East China Sea with Tabu search, OCEANS -2006, 1-4, (2006). 1. Rajan, Potty, Miller, Lynch, Becker and Frisk, Modal inverse techniques for inferring geoacoustic properties in shallow water, in Geoacoustic inversion in Underwater Acoustics, Alex Tolstoy ed., Research Signpost, (submitted in 2007). 2. G. Langer, Phase and travel time variations of acoustic normal modes in shallow water, Masters Thesis, University of Rhode Island, (2007). 3. K. A. Moore, Evaluation of an autonomous underwater vehicle for acoustic surveys, Investigation of 3-D propagation effects at the New Jersey shelf break front and acoustic backscatter in controlled water wave fields, Masters Thesis, University of Rhode Island, (2007). OTHER PUBLICATIONS 1. Gopu Potty, James H. Miller, Ying-Tsong Lin and James F. Lynch, Efficient use of a priori data in sediment inversions through the use of null space, J. Acoust. Soc. Am. 120, 3355 (2006). 2. Kristy A. Moore, James H. Miller, Gopu R. Potty, Georges A. Dossot, Scott M. Glenn, and James F. Lynch, Measurements of 3-D propagation effects at a shelfbreak front, J. Acoust. Soc. Am. 120, 3222 (2006). 3. Steven E. Crocker, James H. Miller, Gopu R. Potty, Georges A. Dossot, and James F. Lynch, Propagation of impulsive broadband signals in a coastal ocean setting during the 1996 Shelfbreak Primer experiment, J. Acoust. Soc. Am. 120, 3221 (2006). 4. Steven E. Crocker, James H. Miller, Gopu R. Potty, and James F. Lynch, Nonlinear optimization for beamforming a geometrically deficient vertical line array: Application to sediment tomography, J. Acoust. Soc. Am. 120, 3063 (2006). 5. J. L. Miksis-Olds and J. H. Miller, Transmission loss in manatee habitats, J. Acoust. Soc. Am. 120, 2320 (2006). 6. Georges A. Dossot, James H. Miller, Gopu R. Potty, Kristy A. Moore, Jason D. Holmes, James F. Lynch, Acoustic measurements in shallow water using an ocean glider, J. Acoust. Soc. Am., 121(5), Pt.2, p3108, (2007). 6

7 7. Gopu R. Potty, James H. Miller, Colin Lazauski, Preston Wilson, James F. Lynch, and Arthur Newhall, Geoacoustic inversion using combustive sound source signals, J. Acoust. Soc. Am., 121(5), Pt.2, p3055, (2007). 8. Kristy A. Moore, James H. Miller, Gopu R. Potty, James Lynch and Arthur Newhall, Investigation of 3D propagation effects at the New Jersey shelf break front, J. Acoust. Soc. Am., 121(5), Pt.2, p3126, (2007). 9. Gregor Langer, James H. Miller, Gopu R. Potty, James F. Lynch, Observation of phase and travel time variations of normal modes during tropical storms Ernesto and Florence, J. Acoust. Soc. Am., 121(5), Pt.2, p3054, (2007). 10. Ivan Zorych, Zoi-Heleni Michalopoulou, James H. Miller, and Gopu R. Potty, Particle filtering for dispersion curve estimation from spectrograms of acoustic signals, J. Acoust. Soc. Am., 121(5), Pt.2, p3171, (2007). (invited). 11. J. H. Miller and J. F. Lynch, The effect of a rough sea surface on acoustic normal modes, J. Acoust. Soc. Am. 121, 3039 (2007) (invited) 12. J. L. Miksis-Olds, P. L. Donaghay, J. H. Miller, P. L. Tyack, and J. A. Nystuen, Noise level correlates with manatee use of foraging habitats, J. Acoust. Soc. Am. 121, 3011 (2007). 13. Herman Medwin, colleagues, and James H. Miller, Reviewer, Sounds in the Sea: From Ocean Acoustics to Acoustical Oceanography, J. Acoust. Soc. Am. 121, 1265 (2007). 14. P. H. Dahl, J. H. Miller, D. H. Cato, and R. Andrew, Underwater ambient noise, Acoustics Today, Vol. 3(1), (2007). 15. James D. Nickila, Kevin B. Smith and Gopu R. Potty, Environmental Influences on the Frequency Dependence of Effective Bottom Attenuation, ICTCA'07, Crete, Greece, (2007) 16. I. Zorych, Z.E. Michalopoulou, J.H. Miller, G.R. Potty, Particle and PHD filters for dispersion curve estimation in underwater acoustics, ICTCA'07, Crete, Greece, (2007) 17. J. H. Miller, J. A. Nystuen, and D. L. Bradley, Ocean Noise Budgets, Presented at the international conference on The Effect of Noise on Aquatic Life, Nyborg, Denmark, (2007). 18. S. K. Tremblay, T. S. Anderson, E. C. Pettit, P. M. Scheifele, J. H. Miller, and G. R. Potty, Ocean Acoustic Effects of Explosions on Land: Evaluation of Cook Inlet Beluga Whale Habitability, Acoust. Soc. Am. Meeting, New Orleans, 2007 (to be presented) 19. G. Dossot, J. H. Miller, G. R. Potty, E. Sullivan, J. D. Holms, J. F. Lynch and S. Glenn, An investigation of the capabilities of a short hydrophone array towed by an ocean glider, Acoust. Soc. Am. Meeting, New Orleans, 2007 (to be presented) 20. G. R. Potty and J. H. Miller, Inversion of compressional wave attenuation of shallow ocean sediments and their frequency dependence, SYMPOL-07, Cochin University of Science and Technology, December, 2007 (to be presented) 21. S. D. Rajan, J. H. Miller and G. R. Potty, Range dependent inversions using multiple broadband sources at the East China Sea, SYMPOL-07, Cochin University of Science and Technology, December, 2007 (to be presented) HONORS/ AWARDS/ PRIZES James Miller was elected as Chair of the Acoustical Oceanography Technical Committee of the Acoustical Society of America George Dossot won the student paper award for the paper presented at the Salt Lake City, ASA Meeting. The paper was titled Acoustic measurements in shallow water using an ocean glider. 7