Long-term underwater acoustic recordings 2013-2019
A long-term spectral average (LTSA) was generated for each site-year to provide a synoptic overview of the quality of each deployment. The resolution of the LTSA was 1 hour in duration and 0.73 Hz (12,000/16384). In addition to the LTSA, one hour of audio from each month was inspected to ensure that...
| Summary: | A long-term spectral average (LTSA) was generated for each site-year to provide a synoptic overview of the quality of each deployment. The resolution of the LTSA was 1 hour in duration and 0.73 Hz (12,000/16384). In addition to the LTSA, one hour of audio from each month was inspected to ensure that there were no gross issues with the recordings. The MAR deployed along the Casey resupply for the 2015 calendar year (Casey2015) was destroyed by the ship during retrieval and no data are available for that year. The MAR deployed along the Casey resupply route for the 2016 calendar year (Casey2016) stopped recording on 2016-07-16, which was earlier than forecast based on expected battery life and storage capacity. This dataset contains long-term underwater acoustic recordings made under Australian Antarctic Science Projects 4101 and 4102, and the International Whaling Commission’s Southern Ocean Research Partnership (IWC-SORP) Southern Ocean Hydrophone Network (SOHN). Calibrated measurements of sound pressure were made at several sites across several years using custom moored acoustic recorders (MARs) designed and manufactured by the Science Technical Support group of the Australian Antarctic Division. These moored acoustic recorders were designed to operate for year-long, deep-water, Antarctic deployments. Each moored acoustic recorder included a factory calibrated HTI 90-U hydrophone and workshop-calibrated frontend electronics (hydrophone preamplifier, bandpass filter, and analog-digital converter), and used solid state digital storage (SDHC) to reduce power consumption and mechanical self-noise (e.g. from hard-drives with motors and rotating disks). Electronics were placed in a glass instrumentation sphere rated to a depth of 6000 m, and the sphere was attached to a short mooring with nylon straps to decouple recorder and hydrophone from sea-bed. The hydrophone was mounted above the glass sphere with elastic connections to the mooring frame to reduce mechanical self-noise from movement of the hydrophone. The target noise floor of each recorder was below that expected for a quiet ocean at sea state zero. The analog-digital converter, based on an AD7683B chip, provides 100 dB of spurious free dynamic range, but a total signal-to-noise and distortion of 86 dB which yields 14 effective bits of dynamic range at a 1 kHz input frequency. The data for each recording site comprise a folder of 16-bit WAV audio files recorded at a nominal sample rate of 12 kHz. The names of each WAV file correspond to a deployment code followed by the start time (in UTC) of the file as determined by the microprocessor’s real-time clock e.g. 201_2013-12-25_13-00-00.wav would correspond to a wav file with deployment code 201 that starts at 1 pm on December 25th 2013 (UTC). Recording locations were chosen to correspond to sites used during AAS Project 2683. These sites were along the resupply routes for Australia’s Antarctic stations, and typically there was only one opportunity to recover and redeploy MARs each year. This multi-year initiative within the Australian Marine Mammal Centre aims to implement a focused acoustic research program that will examine Southern Ocean marine mammal population dynamics through the use of technologically advanced acoustic monitoring techniques. In order to achieve the aims of this study an international collaboration has been developed leading to a multi-faceted research program. Long-term autonomous sea-floor recording devices will be utilised to conduct year-round acoustic surveys in targeted locations. These data will be used to assess distribution, movement, vocalisation density, seasonality, and behaviour of cetaceans in Southern Ocean waters. These results can then be integrated with concurrently collected data on oceanographic and biological variables from vessel based surveys and remote satellite sensing leading to a larger understanding of the role of marine mammals in the Southern Ocean ecosystem. The Southern Ocean Research Partnership (SORP) is an international research program initiated within the International Whaling Commission (IWC) in 2009 to promote collaborative cetacean research, develop novel research techniques, and conduct non-lethal research on whales in the Southern Ocean (SORP, 2009). One of the original research projects of the SORP is the Blue and Fin Whale Acoustic Trends Project, which aims to implement a long term passive acoustic research program to examine trends in Antarctic blue (Balaenoptera musculus intermedia) and fin whale (B. physalus) abundance, distribution, and seasonal presence in the Southern Ocean through the use of a network of passive acoustic recorders: the Southern Ocean Hydrophone Network (SOHN). Networks of widely spaced passive acoustic recorders can provide insights in spatio-temporal patterns of the presence and properties of whale calls as well as the potential to monitor trends in Antarctic blue and fin whale abundance. The SOHN will consist of a network of autonomous underwater acoustic recording stations surrounding the Antarctic continent with each site remaining active throughout the duration of the project. In addition to circumpolar coverage, high priority will be given towards achieving simultaneous temporal coverage, especially in the early years of the project. While logistical constraints may prevent uniform distribution of SOHN recording sites around the continent, the Acoustic Trends Working group (ATW) aims to have at least one recording site in each of the six IWC management areas (i.e., one per 60° longitudinal wedge). International collaboration and coordination are imperative to achieve the project goals due to the high cost of Antarctic research as well as the broad spatial and temporal scales over which the SOHN will span. Furthermore, standardisation of data is paramount for accurate and efficient analysis and interpretation of SOHN data. These data represent Australia’s contribution to the IWC-SORP/SOOS Acoustic Trends Project and Southern Ocean Hydrophone Network. |
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