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Scattering from extended targets in range-dependent fluctuating ocean-waveguides with clutter from theory and experiments
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10.1121/1.4726073
/content/asa/journal/jasa/132/2/10.1121/1.4726073
http://aip.metastore.ingenta.com/content/asa/journal/jasa/132/2/10.1121/1.4726073

Figures

Image of FIG. 1.
FIG. 1.

(A) Location of the NJ2001 and the NJ2003 experiments off the coast of New Jersey. Black dashed circle shows 60-km diameter areal imaging coverage in 40 s. (B) and (C) Geometry of the experiments showing the location of the moored source, the targets, and two receiver tracks in each experiment from which measured target-scattered received levels are used for comparisons with models. The zoom area is shown as a black box in (A). The grayscale shows the relatively flat bathymetry in the region.

Image of FIG. 2.
FIG. 2.

(A) Location of the GOM2006 experiment in the Gulf of Maine. Bathymetric contours are marked with grey lines. Black dashed circle shows 100-km areal imaging coverage in 75 s. (B) Geometry of the experiment showing the location of the moored source, the targets, and the receiver track from which measured target-scattered received levels are used for comparisons with models. The zoom area is shown as a black box in the left figure. The grayscale shows the highly variable bathymetry in the region.

Image of FIG. 3.
FIG. 3.

Discrete, consistent and strong acoustic returns from man-made targets were recorded during (A) NJ2001, (B) NJ2003, and (C) GOM2006. Examples of Ocean Acoustic Waveguide Remote Sensing (OAWRS) sound pressure-level (SPL) image, zoomed around the region of targets, normalized to 0 dB source-level, obtained on (A) May 1, 2001 at 10:58:15 GMT (Ref. 2), (B) May 9, 2003 at 21:19:55 GMT, and (C) October 2, 2006 at 23:10:00 GMT. A linear frequency modulated (LFM) 1-s long pulse with center frequency 415 Hz and bandwidth of 50 Hz was used to form the images. Black lines mark the 80 -m isobath in (A) and (B) and the 200 -m isobath in (C).

Image of FIG. 4.
FIG. 4.

Examples of typical matched-filter output of man-made target-scattered data recorded during NJ2003. (A)—(C) Transmitted linear frequency modulated (LFM) signal envelope; normalized matched-filter (MF) output of the LFM waveform; and signal spectrum. (D)—(F) Example of envelope of received target-scattered signal before matched filtering recorded on May 9, 2003 at 18:28:15 GMT; the MF output [computed using Eq. (10)] showing sharp, well localized target-return plotted as a function of two-way travel time; and frequency spectrum of the received signal in (D). (G)—(I) Example of envelope of received target-scattered signal before matched-filtering recorded on May 9, 2003 at 18:31:35 GMT (3 min later than D), the MF output [computed using Eq. (10)] showing weak, dispersed, less well-localized target-return plotted as a function of two-way travel time and frequency spectrum of the received signal in (G). Dispersed target returns were observed in roughly 25% of all target returns in NJ2003.

Image of FIG. 5.
FIG. 5.

Sonar Equation-derived targets strengths (TS) of man-made targets vs fish [ vs , Eq. (1)]. Black dashed circles are used to denote mean TS of man-made targets and gray triangles are used to denote TS for fish. (A) vs measured on May 9, 2003, during NJ2003. Vertical bars are the standard deviations of the target strength estimates. A total of 85 transmissions from Track 201 were used for estimating at 415 Hz. A total of 90 transmissions from track 202 were used for estimating at 925 and 1325 Hz. To estimate , data from both May 9 and May 14 were used as described in Ref. 7. (B) tgt vs measured on Oct. 2, 2006, during GOM2006. A total of 20 transmissions from Track 571 were used for estimating at each frequency shown. To estimate , data from Oct 2. was used as described in Ref. 9.

Image of FIG. 6.
FIG. 6.

Geometry (not to scale) showing target-centered cylindrical coordinate system used in the Vertically Extended Cylindrical Target Waveguide Scattering (VETWS) model. The cylinder has length L and radius a. The non-iso sound speed structure over the depth of the man-made extended target, measured during NJ2001, NJ2003 and GOM2006 (gray lines) and their means (black lines) are shown to the right.

Image of FIG. 7.
FIG. 7.

Comparison of man-made target-scattered levels modeled using the VETWS, Ingenito, and Sonar Equation models relative to the mean scattered level measured during (A) Track 14 of NJ2001 and (B) Track 17 of NJ2001. The center frequency of the source is 415 Hz. Black triangles show the measured target-scattered levels for 19 transmissions made during Track 14 and 20 transmissions made during Track 17, relative to the mean measured level. The standard deviations (SD) of the data for both tracks are 2.5 dB and are marked with solid black vertical lines. The SD of the simulated scattered levels using different models are computed based on Eqs. (15) and (16), and are (1) VETWS: 1.3 dB (Track 14) and 0.93 dB (Track 17); (2) Ingenito model: 2.26 dB (Track 14) and 0.6 dB (Track 17), and (3) Sonar Equation model: 1 dB (Track 14) and 0.7 dB (Track 17).

Image of FIG. 8.
FIG. 8.

Comparison of man-made target-scattered levels modeled using the VETWS, Ingenito, and Sonar Equation models relative to the mean scattered level measured during (A) Track 201 and (B) Track 202 of NJ2003. The center frequencies of the source are 415 Hz in Track 201 and 950 Hz in Track 202. Black triangles show the measured target-scattered levels for 89 transmissions made during Track 201 and 90 transmissions during Track 202, normalized to the mean measured scattered level. The SDs of the measurements and the simulated scattered levels using different models are marked with vertical lines and are (1) Data: 3.8 dB (Track 201) and 2.3 dB (Track 202), (2) VETWS: 1 dB (Track 201) and 1.3 dB (Track 202), (3) Ingenito model: 1.2 dB (Track 201) and 3.5 dB (Track 202), and (4) Sonar Equation model: 0.7 dB (Track 201) and 0.5 dB (Track 202).

Image of FIG. 9.
FIG. 9.

Comparison of man-made target-scattered levels modeled using the VETWS, Ingenito, and Sonar Equation models relative to the mean scattered level measured during Track 571 of GOM2006 for different source center frequencies (A) 415 Hz, (B) 735 Hz, (C) 950 Hz, and (D) 1125 Hz. Black triangles show the measured target-scattered levels for 10 transmissions when the targets were clearly visible (SNR > 10 dB) during Track 571, normalized to the mean measured scattered level. Fewer transmissions were made per track per frequency during GOM2006 than in NJ2001 and NJ2003. The SDs of the measurements and the simulated scattered levels using different models are marked with vertical lines. For the different frequencies in (A)—(D), the SDs are, respectively, (1) Data: 2.7, 2.7, 3.9, and 5.9 dB; (2) VETWS: 1.2, 0.9, 2, and 1.4 dB; (3) Ingenito model: 2.5, 1.6, 3, and 5.8 dB; and (4) Sonar Equation model: 1.2, 1.1, 0.8, and 0.4 dB.

Image of FIG. 10.
FIG. 10.

Square of the base-band envelope of the matched filtered scattered returns from man-made, air-filled cylindrical targets simulated using the VETWS model for different oceanographic conditions in the New Jersey environment. The different dominant acoustic modes are marked in gray. The modes combine either constructively or destructively to form the total scattered return, which is marked in black. (A) Example of sharp, well-localized return from target with most of the scattered energy concentrated in the first two modes. (B) Example of dispersed return from target with scattered energy distributed across more modes than in (A). The same source-receiver-target geometry of (A) was used but with a different sound speed profile.

Image of FIG. 11.
FIG. 11.

Effect of target tilt on received pressure levels. Simulations of target-scattered levels, computed using a modified VETWS model described in Sec. VI as a function of target-tilt angle for two different frequencies used during NJ2003. A monostatic source-receiver configuration as described in Sec. VI is used. The target is assumed to tilt in the plane formed by the vertical through the target center and the source location.

Tables

Generic image for table
TABLE I.

Parameters used for modeling target scattering.

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/content/asa/journal/jasa/132/2/10.1121/1.4726073
2012-08-08
2014-04-19
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Scattering from extended targets in range-dependent fluctuating ocean-waveguides with clutter from theory and experiments
http://aip.metastore.ingenta.com/content/asa/journal/jasa/132/2/10.1121/1.4726073
10.1121/1.4726073
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