Top-down view of a bistatic active sonar network. The bistatic range is defined as . The axis is used as a reference for the source and target azimuth angle in the next section.
Single path invariant for the configuration shown in Fig. 1. (a) Time–frequency dependency for the leg; (b) time–frequency dependency for the leg; (c) (solid line) and (dotted line) as a function of time.
Simulation of a bistatic spectrogram for the configuration shown in Fig. 1: (a) Bistatic spectrogram for the full path source–target–receiver. The corresponding single leg spectrograms are shown in Fig. 2; (b) as a function of time. The scattering strength was computed using Eq. (27) from Ingenito (Ref. 8).
(a) Map showing the SWAC experiment (Ref. 10). Three different targets are highlighted: An oil rig moored tanker (○), Wreck 1 (◇), and Wreck 2 (▵). T1 (solid line), T2 (dash-dot line), and T3 (dashed line) are the corresponding GPS tracks followed by the towed sonar; (b) observed sound speed profile for the SWAC experiment. The three measurements correspond to the days 25 October 1994 at 13:53 Greenwich Mean Time (GMT) (dashed line), 26 October 1994 at 12:01 GMT (solid line), and 26 October 1994 at 18:34 GMT (dotted line). Water depth is .
(a) Output of the matched filter for the first ping in (b); (b) example of the windowed match-filtered output for a track of 174 pings , associated with the moored tanker target in Fig. 4(a).
The system response corresponds to the ocean channel as given by Eq. (6), and includes the two-way wave propagation and the target scattering effects. The impulse response of the receiver is .
(a) Spectrogram for a moored tanker (Target N.3, track N.56 from NUWC database). The data were collected on 26 October 1994 at 9:48 GMT; (b) superimposed guidelines highlight the main striations; and (c) GPS measurement of range as a function of time.
Spectrogram simulations for the moored tanker track shown in Fig. 7. Two different scattering matrices were considered: (a) No intermode coupling and (b) Lambertian model.
(a) Bistatic spectrogram corresponding to the tracking of the Wreck 1 (Target N.9, track N.3 from NUWC database). The data were collected on 26 October 1994 at 20:03 GMT; (b) a monotonically decreasing range as a function of time results in striations with the same orientation; and (c) simulated spectrogram using a Lambertian scattering matrix and the sound speed profile in Fig. 4(b) (dotted line).
(a) Bistatic spectrogram corresponding to the tracking of Wreck 2 (Target N.8, track N.23 from NUWC database). The data were collected on 26 October 1994 at 14:12 GMT; (b) the range was estimated by the sonar system instead of GPS; and (c) simulated bistatic spectrogram using a Lambertian scattering matrix and the sound speed profile in Fig. 4(b) (dashed line).
(a) Straight striation in the spectrogram of Fig. 9, detected with the Radon transform and (b) Radon domain corresponding to the picture shown in Fig. 11(a).
Simulation of the spectrogram in Fig. 7 for a midfrequency of with two different bandwidths: 120 and . In both cases, Lambertian scattering matrix was used.
Geoacoustic parameters for the Malta Plateau used to compute simulated spectrograms with KRAKEN (Ref. 9) normal modes.
Main experimental parameters for the Malta Plateau experiment.
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