(Color online) Experimental environment and acoustic measurement geometries on April 23, 2007. Contours lines are the thickness of the upper sediment layer reconstructed from the seismic survey. The color bar illustrates the water depth distribution. The solid line indicates the track of the NRV Leonardo (run L#2) for passive measurement. The short dashed line is the corresponding course of the drifting rigid hulled inflatable boat (RHIB), which deployed the ocean-acoustic array (OAA). Active acoustic measurements were performed in the same area, the source of which was deployed from NRV Leonardo (cross); the OAA was also deployed from RHIB, which drifted slowly toward to the source (long dashed line). The start and end points of each course are indicated by a square and a dot, respectively.
(Color online) Water column SSP taken by the NRV Leonardo at the start point of the run L#2 of MREA/BP'07 sea trial, 23 Apr 2007.
(Color online) Spectrogram of the acoustic pressure field recorded on the hydrophone with an average depth of 19.6 m during passive run L#2 of MREA/BP07 sea trial. The horizontal line indicates the closet point of approach time.
(Color online) Part of acoustic pressure spectrogram of Fig. 3 after mapping into frequency-range plane by re-sampling along the time axis.
(Color online) The predicted sound field interference structures for the (a) SB model, (b) one SFB model and, (c) the SF model.
(Color online) Correlation coefficients of the interference structure of the SFB models with approximated models (solid line for the SB model and dashed line for the SF model) for the frequency bands of (a) 50–1000 Hz, (b) 50–400 Hz, (c) 400–750 Hz, (d) 750–1000 Hz.
(Color online) The calculated line-like structure of Fig. 4 by the multi-scale line filter.
(Color online) The calculated line-like structure of the predicted interference structure for the reference sediment with a thickness ( ) and sound speed ( ) of 0.5 m and 1460 m/s, respectively. Four low-frequency striation segments are selected to study the average effect of environmental perturbations on striation shift.
(Color online) The for L1 in Fig. 8 with respect to (a) for different , m for the top curve and 8 m for the bottom curve with an increment of 0.5 m and (b) for different , 1520 m/s for the top curve and m/s for the bottom curve, with a decrement of 10 m/s.
(Color online) The calculated line-like structures of ship noise spectrogram (top of each sub-figure) and corresponding simulated interference structures with the reference sediment (bottom of each sub-figure) for receivers 1, 2, 3, and 4 with, respectively, depths of (a) 34.0 m, (b) 29.2 m, (c) 24.4 m, and (d) 19.6 m. The lower-frequency boxed striations for both data and corresponding reference sediment are used for calculation for each receiver (the longer dashed lines in the data correspond to that of reference sediment). The higher-frequency boxed striations are used for refinement.
(Color online) Preliminary estimations of and given by Eq. (13) for different receivers. Each filled quarter circle represents the solutions by different receivers: Top-left for receiver 1, 34.0 m, T-R: R2, 29.2 m, B-L: R3, 24.4 m, B-R: R4, 19.6 m.
(Color online) The radon transform results for the selected frequency-range box in Fig. 11 for receivers 1, 2, 3, and 4 with depths of (a) 34.0 m, (b) 29.2 m, (c) 24.4 m, and (d) 19.6 m, respectively.
(Color online) The calculated correlation coefficients for the receiver with depths of (a) 34.0 m, (b) 29.2 m, (c) 24.4 m, (d) 19.6 m, and (e) the average of their normalized correlation coefficients. The highest value for each figure is indexed by a cross.
(Color online) The calculated correlation coefficients for the receiver 1 with different range errors of (a) −20 m, (b) −10 m, (c) +10 m, and (d) +20 m for the selected frequency-range regions with respect to that of Fig. 14(a) .
Geoacoustic parameters of different environment models. The core based model (SFB) is featured by a soft layer, a fast layer and a bottom layer. There is no fast layer for the SB model and the SF model treats the fast layer as a sub-bottom.
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