Lake tests in summer 2021 (CCRI Year 1)
Summary: Multiple field experiments will be conducted in summer 2021 to collect mobile underwater acoustic measurements. In these experiments, one or two autonomous underwater vehicles (AUVs) will be deployed in a 20-m lake. Acoustic modems installed on the AUVs will be used to transmit user-provided waveforms. An eight-element hydrophone array will be deployed off a boat to record acoustic transmissions from the mobile nodes. The acoustic measurements will be distributed to the users and shared with the CISE communities.
Location: Lake of Tuscaloosa, Tuscaloosa, Alabama. The experimental site has a water depth of about 20 m; see Figure 1 for the site, about 1 km by 1 km in size.
Main instruments for field tests include (a) Mid-size AUV, EcoMapper (two EcoMappers in July 2021). (b) A software-defined acoustic modem from Subnero on the AUV. (c) Eight wideband digital hydrophones. (d) Handheld CTD.
Experimental setup
- One or two mobile nodes, the EcoMapper AUV, are available. Software-defined acoustic modems are installed on the EcoMapper AUVs.
- An 8-element digital hydrophone array is hung from a boat to perform acoustic recordings.
- AUV missions: The EcoMapper AUVs will travel in rectangular tracks with different vehicle depths. Each AUV mission lasts about one hour.
- Acoustic modems on the AUVs are the transmitters, while the 8-element hydrophone array is the receiver.
Transmitter and receiver characteristics
| Transmitter (single transducer for each AUV) | |
| Center frequency | 24 kHz |
| Bandwidth range | 20 to 32 kHz |
| Sampling frequency | 192 kHz |
| Source level (max) | 185 dB rel 1 µPa |
| Transmit voltage response flatness | +/- 4 dB |
| Transducer duty cycle | 50% at full source level; 100% at the 10 dB-reduced level |
| Receiver (eight hydrophones) | |
| Bandwidth | 2 Hz to 200 kHz |
| Sampling frequency | 128, 256, or 512 kHz |
| Hydrophone sensitivity | -176 dBV re µP at 20-30 kHz |
| Sensitivity variation in 20-30 kHz or across the elements | +/- 2 dB |
| Waveform format | .wav |
| Synchronization offsets among array elements | < 5 ms |
Transmission waveform format
We ask you to provide .wav files (single channel) with a sampling rate of 192 kHz. The waveform should be normalized to the range of [-1, 1]. An absolute amplitude of one corresponds to the transmission of the maximum source level, 185 dB. The maximum duration of the waveform is 10 seconds per file. You may send in multiple 10-s files. We also ask you to provide source transmission files and programs (that produce the waveforms).
Distribution of experimental measurements
The following data will be shared to the users and community. We ask the users to acknowledge the source of the data, the NSF CCRI project, “mu-Net: Infrastructure to Advance Mobile Underwater Wireless Networking Research,” CNS#2016726 and #2016582. We welcome the users to work with us to provide the processed data to the user community for research and education.
- Experimental plan and notes
- Environmental measurements: Site water depth survey and water temperature
- Acoustic source information and transmitted waveform
- Acoustic recordings from the 8-element array
We welcome suggestions and comments. Please contact us, team@aquatictech.org, should any questions or suggestions arise.