The Development of a Low-Cost Hydrophone for Passive Acoustic Monitoring of Dolphin’s Vocalizations
Abstract
:1. Introduction
2. Materials and Methods
2.1. Hardware Architecture
2.1.1. The Hydrophone
2.1.2. The Preamplifier
2.2. Experimental Validation
2.2.1. Recording of Artificial Acoustic Signals
- A homemade signal source device consisting of a piezo disk mounted inside a floating metallic can (diameter 7 cm and height 4 cm) and powered by a Tektronix CFG253 signal generator. This device generates cyclically variable 20-Vpp sine waveform signals with a frequency in the interval between 0 and 100 kHz (ramp signal). The cycle duration is 1.7 s;
- An acoustic deterrent device or “pinger” (DDD, manufactured by S.T.M. Products, Italy) with remote wired activation, emitting sounds within the frequency range of 5 to 500 kHz with an emission power of 165 dB (1 µPa @ 1 m) and operating at a depth of 70 cm. The device produces multiple sweeping signals and a 30-s cycle of multitone impulses (Figure 4). The multitone impulses were analyzed in the experimental activities.
- The first piezo disk is orthogonal to the direction of the emission; the other disk is on the opposite side of the device—position 0°;
- Both piezo disks are parallel to the direction of the emission—position 90°;
- The second piezo disk is orthogonal to the direction of the emission and the other disk is on the opposite side of the device—position 180°;
- The sound emission strikes the bottom part of the hydrophone orthogonally–horizontal (H).
2.2.2. Recording Dolphin Vocalizations
2.3. Data Analysis
2.3.1. Artificial Acoustic Signals
- For ramp signals, the Fourier Transform (FFT, size = 1024) was computed in 7-ms windows in order to provide the power spectral density (PSD). A 7-ms window was chosen because the frequency is considered stable in this interval. The CoPiDi hydrophone’s performance was evaluated by comparing its PSD to that of the reference. Wave files were processed using GNU Octave software;
- For multitone signals, 30 s of the recorded signal were processed in order to extract a series of single multitone segments of variable length as follows: the signal was scanned to identify the samples where the signal amplitude is ≈0 dB (no signal) in the whole frequency range (0–96 kHz). These no-signal areas were then used to split the whole signal in the multitone segments. Each segment is composed of consecutive signal-area samples (signal amplitude > 0) included between two successive no-signal areas. The Fourier transform (FFT, size = 1024) and PSD were then computed in each single segment. PSD values exceeding the empirically identified threshold of 3.50 × 10−3 dB/Hz (used to filter out noise) were compared between the proposed and reference hydrophones. The GNU Octave software was used for this processing.
2.3.2. Dolphin Vocalizations
Click Identification
Identification of Whistles and Burst Pulse Signals
2.4. Preamplifier Validation
3. Results
3.1. Artificial Acoustic Signals
3.2. Dolphin Vocalizations
4. Discussion
5. Conclusions
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Trial | Source | Orientation | Preamplifier |
---|---|---|---|
1 | Ramp signal | 0° | Triton |
2 | Ramp signal | 90° | Triton |
3 | Ramp signal | 180° | Triton |
4 | Ramp signal | H | Triton |
5 | Ramp signal | 0° | Homemade |
6 | Ramp signal | 90° | Homemade |
7 | Ramp signal | 180° | Homemade |
8 | Ramp signal | H | Homemade |
9 | Multitone signal | 0° | Triton |
10 | Multitone signal | 90° | Triton |
11 | Multitone signal | 180° | Triton |
12 | Multitone signal | H | Triton |
13 | Multitone signal | 0° | Homemade |
14 | Multitone signal | 90° | Homemade |
15 | Multitone signal | 180° | Homemade |
16 | Multitone signal | H | Homemade |
17 | Environmental noise | 0° | Triton |
18 | Environmental noise | 0° | Homemade |
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De Marco, R.; Di Nardo, F.; Lucchetti, A.; Virgili, M.; Petetta, A.; Li Veli, D.; Screpanti, L.; Bartolucci, V.; Scaradozzi, D. The Development of a Low-Cost Hydrophone for Passive Acoustic Monitoring of Dolphin’s Vocalizations. Remote Sens. 2023, 15, 1946. https://doi.org/10.3390/rs15071946
De Marco R, Di Nardo F, Lucchetti A, Virgili M, Petetta A, Li Veli D, Screpanti L, Bartolucci V, Scaradozzi D. The Development of a Low-Cost Hydrophone for Passive Acoustic Monitoring of Dolphin’s Vocalizations. Remote Sensing. 2023; 15(7):1946. https://doi.org/10.3390/rs15071946
Chicago/Turabian StyleDe Marco, Rocco, Francesco Di Nardo, Alessandro Lucchetti, Massimo Virgili, Andrea Petetta, Daniel Li Veli, Laura Screpanti, Veronica Bartolucci, and David Scaradozzi. 2023. "The Development of a Low-Cost Hydrophone for Passive Acoustic Monitoring of Dolphin’s Vocalizations" Remote Sensing 15, no. 7: 1946. https://doi.org/10.3390/rs15071946
APA StyleDe Marco, R., Di Nardo, F., Lucchetti, A., Virgili, M., Petetta, A., Li Veli, D., Screpanti, L., Bartolucci, V., & Scaradozzi, D. (2023). The Development of a Low-Cost Hydrophone for Passive Acoustic Monitoring of Dolphin’s Vocalizations. Remote Sensing, 15(7), 1946. https://doi.org/10.3390/rs15071946