Brief description The Portland Passive Acoustic Observatory consists of two to four moorings fitted with hydrophones set on the seabed at ~170 m depth that record noise in the ocean. This system can be used to monitor whale and fish migrations, seismic activity and other natural and man-made noise sources. If four moorings are set they are configured with a mooring at each apex of an approximate equilateral triangle of 5 km side with the fourth mooring in the triangle centre. Temperature loggers are set on each mooring at the seabed.
Each logger records at a sampling rate of 6 kHz for between 3-8 min of every 15 min. If four loggers are set a 22 kHz recording is also made once a day to allow accurate synchronisation of the instrument clocks. This is required for locating the source of a sound based on its time of arrival at each hydrophone in the array. A 7 kHz pinger set on the central mooring pings for 35 minutes at a 20 s interval once per day to overlap the 22 kHz sample.
Raw data from each logger is in the form of mixed binary/text files comprised of:
1) text header and footer containing recording start and end date/time, quality control and sampling configuration; and
2) sea noise data of 16 bit unsigned integer, binary values (IEEE, little endian).
Instruments are calibrated for system gain with white noise of known level input with the hydrophone in series, before and after deployments. System calibrations are made over 2 Hz to the Nyquist frequency. The instrument clock drift is checked against GPS transmitted UTC time before and after deployment.
The raw data can be obtained on portable disk from IMOS eMarine Information Infrastructure (eMII).
The Centre for Marine Science and Technology (CMST) at Curtin University has developed Matlab software to process and analyse these data.
This observatory was decommissioned early in 2018.
Australia’s Integrated Marine Observing System (IMOS) is enabled by the National Collaborative Research Infrastructure Strategy (NCRIS). It is operated by a consortium of institutions as an unincorporated joint venture, with the University of Tasmania as Lead Agent.