IMOS - ANMN Passive Acoustic Observatory at Perth Canyon, WA (PAPCA)

Brief description

The Perth Canyon Passive Acoustic Observatory consists of two to four moorings fitted with hydrophones set on the seabed at 400-490 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 in October 2017.

Lineage

Maintenance and Update Frequency: continual

Statement: 1. Five day stacked power spectra
In order to visualise the sea noise data it has been displayed as colour images with time as the x-axis, log-frequency as the y-axis and colour as the intensity, in calibrated spectral level units with the scale given by the colour bar. The colour scale bounds are fixed to standardise the plots and optimise the colour dynamic range. Values below the lower bound or above the upper bound are set to the respective colour at the boundary.
These plots were made by taking the averaged power spectra across each sample at three frequency resolutions and stacking a combination of these averaged spectra in five day blocks on the colour plot. The figures are displayed with a logarithmic frequency scale from 10 Hz to 2800 Hz (the upper calibrated limit of the recording system). The system was calibrated down to 1 Hz.
Various noise sources are apparent on the plots, such as pygmy blue whales (horizontal banding between 18-75 Hz with distant animals always contributing over January to April in the Perth Canyon, and periods of nearby animals easily evident), vessels (vertical banding of a few hours across 10 Hz to a few hundred Hz or up to a kHz) evening fish choruses (just after dusk for a few hours with most energy > 1 kHz) or wind noise with most energy from 100 Hz up to a few kHz and which comes and goes at half day to many day time scales.

2. Counts of pygmy blue whales
The Perth Canyon data sets have pygmy blue whales which appear mostly over January to May each year. We have an in-house algorithm which counts the numbers of individual calling pygmy blue whales in each sample. The data is then averaged over a 24 hour period to account for known day-night differences in calling behaviour, and plotted as the 24 hour mean count of individual pygmy blue whales with 95% error bars shown. The sampling period is shown by the red line at the bottom and days with zero whale counts are not highlighted on the figure. The data is presented as output by the algorithm and has not been cross checked for accuracy.

Notes

Credit
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.