This dataset contains acoustic recordings from Directional Frequency Analysis and Recording (DIFAR) sonobuoys that were deployed from 19 January – 5 March 2019 during the ENRICH (Euphausiids and Nutrient Recycling in Cetacean Hotspots) voyage. 295 sonobuoys were deployed yielding 828 hours of acoustic recordings.

Passive acoustic research during ENRICH took the form of both broad-scale structured surveys and fine-scale adaptive surveys depending on the operational mode of the ship. Regardless of the mode of operation, listening stations were conducted by deploying SSQ955 sonobuoys (commonly called HIDAR sonobuoys) in Directional and Frequency Analysis and Recording (DIFAR) mode to monitor for and measure bearings to vocalising whales while the ship was underway (Miller et al. 2015). During transit, listening stations were conducted every 30 nmi in water depths greater than 200 m when Beaufort sea state was less than 7. During marine science stations, sonobuoys were deployed approximately 2-4 nmi prior to stopping in order to attempt to monitor them for the full six-eight hour duration of their operational life or the duration of the station. The sampling regime was chosen for compatibility with previous surveys, and to balance spatial resolution with the finite number of sonobuoys available for this study.

During portions of the voyage dedicated to passive acoustic tracking, multiple sonobuoys were deployed concurrently to precisely locate Antarctic blue whales (Miller et al. 2015, 2016). Bearings from single sonobuoys, pairs, or triplets were also followed in order to track, locate, and sight blue whales to obtain visual observations of group size, behavior, and photographic identifications. Tracking was conducted during 10 days spread throughout the voyage: 30 Jan, and 2, 5, 9, 13, 17, 19, 22-24 Feb 2019 for a total of 124.1 hours. When conducting activities with whales, sonobuoys were deployed adaptively, often in pairs or triplets with 6-9 nmi spacing. When possible during acoustic tracking, the acousticians also continued to monitor other groups of whales that were judged to be nearby (e.g. within a 20-30 nmi radius of the array), as well as more distant animals. Triplets of sonobuoys were also occasionally deployed during small-scale active acoustic surveys even if there was no opportunity to approach whales.

Instrumentation, software, and data collection

At each listening station, a sonobuoy was deployed with the hydrophone set to a depth near 140 m. Sonobuoys transmitted underwater acoustic signals from the hydrophone and directional sensors back to the ship via a VHF radio transmitter. Radio signals from the sonobuoy were received using an omnidirectional VHF antenna (PCTel Inc. MFB1443; 3 dB gain tuned to 144 MHz centre frequency) and a Yagi antenna (Broadband Propagation Pty Ltd, Sydney Australia) mounted on the aft handrail of the flying bridge. The antennas were each connected to a WiNRADiO G39WSBe sonobuoy receiver via low-loss LMR400 coaxial cable.

The radio reception range on the Yagi antenna was similar to previous Antarctic voyages, and was adequate for monitoring and localisation typically out to a range of 10-12 nmi, provided that the direction to the sonobuoy was close (i.e. within around 30o) to the main axis of the antenna. The radio reception on the omnidirectional antenna typically provided 5-10 nmi of omnidirectional reception from sonobuoys. At transit speed (8-11 knots), the Yagi antenna provided about 75 minutes of acoustic recording time per sonobuoy. Using both antennas together were able obtain radio reception for up to six hours (i.e. the maximum life of a 955 sonobuoy) when sonobuoys were deployed within 5 nmi of a marine science station.

Received signals were digitised via the instrument inputs of a Fireface UFX sound board (RME Fireface; RME Inc.). Digitised signals were recorded on a personal computer as 48 kHz 24-bit WAV audio files using the software program PAMGuard (Gillespie et al. 2008). Data from both the Yagi and Omnidirectional antennas were recorded simultaneously as WAV audio channels 0 (left) and 1 (right) and 2. Each recorded WAV file therefore contains a substantial amount of duplication since both antennas and receivers were usually receiving the same signals from the same sonobuoy.

Directional calibration

The magnetic compass in each sonobuoy was not calibrated/validated upon deployment because the ship did not generate enough noise.

Intensity calibration

Intensity calibration and values followed those described in Rankin et al (2019).

Sonobuoy deployment metadata

The PAMGuard DIFAR Module (Miller et al. 2016) was used to record the sonobuoy deployment metadata such as location, sonobuoy deployment number, and audio channel in the HydrophoneStreamers table of the PAMGuard database (In2019_V01.sqlite3). A written sonobuoy deployment log (SonobuoyLog.pdf) was also kept during the voyage, and this includes additional notes and additional information not included in the PAMGuard Database such as sonobuoy type, and sonobuoy end-time.

Real-time monitoring and analysis:

Aural and visual monitoring of audio and spectrograms from each sonobuoy was conducted using PAMGuard for at least 5 minutes after deployment only to validate that the sonobuoy was working correctly.

Additional information about sonobuoys is contained in the file: Sonobuoy data collection during the TEMPO voyage - 2021-01-15.pdf

References

Greene, C.R.J. et al., 2004. Directional frequency and recording ( DIFAR ) sensors in seafloor recorders to locate calling bowhead whales during their fall migration. Journal of the Acoustical Society of America, 116(2), pp.799–813.

Miller, B.S. et al., 2016. Software for real-time localization of baleen whale calls using directional sonobuoys: A case study on Antarctic blue whales. The Journal of the Acoustical Society of America, 139(3), p.EL83-EL89. Available at: http://scitation.aip.org/content/asa/journal/jasa/139/3/10.1121/1.4943627.

Miller, B.S. et al., 2015. Validating the reliability of passive acoustic localisation: a novel method for encountering rare and remote Antarctic blue whales. Endangered Species Research, 26(3), pp.257–269. Available at: http://www.int-res.com/abstracts/esr/v26/n3/p257-269/.

Rankin, S., Miller, B., Crance, J., Sakai, T., and Keating, J. L. (2019). “Sonobuoy Acoustic Data Collection during Cetacean Surveys,” NOAA Tech. Memo. NMFS, SWFSC614, 1–36.