Fig 1.
The boundaries of the Portofino MPA and the position of the three different zones with restricted acces are reported on the map. The round areas centered on the two acoustic units represent the monitoring area of the PAM system.
Fig 2.
Plot of the signal-to-noise ratio level as a function of the source-to-receiver distance for different sea-state conditions.
The maximum detection range of the system, for a selected sea-state, is obtained by crossing the 5 dB detection threshold (dashed line) with the corresponding signal-to-noise level curve (solid line).
Fig 3.
Scheme of the acoustic unit.
Fig 4.
Scheme of the data flow.
Fig 5.
The online panel.
Fig 6.
Time series (top) and spectrogram (bottom) of multiple bottlenose dolphin whistles recorded next to the Tuscany coast in May 2012.
Fig 7.
Steps of the whistle detection algorithm.
Top: binary spectrogram resulting from click suppression. Middle: first derivative of the binary spectrogram. Bottom: boolean whistle detection function.
Fig 8.
Frequencies of cetacean moans and whistles.
The red band corresponds to the portion of the spectrum involved in the detection algorithm. Reprinted from [48] under a CCBY license, with permission from The Oceanography Society, original copyright 2007.
Fig 9.
Correlation plot (frequency slope vs time duration) of 2574 detections.
Whistles (black square), mooring cable (red triangle), small boats (green triangle). The origin of each signal was found by visual inspection of the corresponding spectrogram.
Fig 10.
Panels extracted from the TDOA calculation routines.
Top: spectrograms of a dolphin whistle at the four hydrophones. Bottom: corresponding cross-correlation plots of the six hydrophone pairs combinations. This whistle was recorded by the PAM system on October, 15th, 2013 at 02:43 a.m. (UTC).
Fig 11.
Diagram of the sound wavefront running over i-th hydrophone in the simple case of compass ψ = 0 and ψ0 = 0.
When the wavefront reaches the sensor, it belongs to that plane. The azimuth (φW) and elevation (ϑW) angles of the incident acoustic wave are also shown in the diagrams at the bottom.
Fig 12.
Scheme of the acoustic source position with respect to the hydrophone array.
The azimuth (α) and elevation angles (β) are represented in the top view (left) and side view (right) of the scheme, respectively.
Fig 13.
Scheme of boat tracking algorithm.
(A)cross-correlogram (cross-correlation as a function of time) of each hydrophone pair. (B)probability functions of target direction associated to each hydrophone pair. (C)resulting probability function of target direction. (D)polar graph of the target direction in the world coordinate system.
Table 1.
Summary of the PAM system working efficiency.
Fig 14.
Dolphin tracking event recorded by the PAM system on December, 13th 2013.
Panels from 1 to 9 show the dolphin pod direction calculated by the tracking algorithm as a function of time.
Fig 15.
Dolphin pod localization event recorded by the PAM system on June, 13th 2013.
Top: position of the dolphin pod calculated by applying triangulation to the directions (straight dashed lines) of the target to each acoustic unit. The curve dashed line represents the locus of points of equal TDOA at the acoustic units. Bottom left (right): spectrogram of the specific whistle recorded by Punta Carega (Casa Sindaco) unit for the calculation.
Fig 16.
Boat tracking event recorded on March, 23rd 2015.
The panel shows a 5 km route of a passenger vessel moving in the study area. The red circles correspond to the position of the boat every 1 second, as reconstructed by the PAM system. The boat-shaped placemarks correspond to the AIS-recorded position of the boat. The good correspondence confirms the efficiency of the boat tracking algorithm.
Fig 17.
Snapshot of the alarm generation web portal.
Each dolphin detection event is visualized on the map by highlighting the corresponding sector. This information is available to the local Coast Guard operators that are responsible for the alarm generation.