The passive acoustic observatories record sound emitted by natural processes in the ocean, underwater noise sources of biological origin, such as marine mammals, crustaceans or fish, plus man-made noise sources. Through analysis of these signals it is possible to discriminate and identify different animal species and to assess the number of animals present within the range of acoustic observation, which can then be linked to ocean productivity or yearly migratory passage for great whales. Sea noise can be visualised on the IMOS Acoustic Data Viewer, small amounts downloaded or large amounts requested from IMOS. Data is currently supplied in its raw format only, although we are considering making available processed detection times of various whales for selected sites.
Instrumentation and Data
The passive acoustic observatories comprise a sea noise logger placed on the ocean floor attached to a mooring which on command, releases floats to the surface. The sea noise loggers were designed and built at Curtin University and are well proven fully calibrated instruments. Each mooring also has ancillary temperature loggers attached with one on the seafloor and one between 30-50 m above the seafloor.
Sea noise data sets can be viewed via the IMOS Acoustic Data Viewer, as time stacked spectrograms (~ 15 days, x-scale) on a logarithmic frequency scale (y-scale, 5 Hz to 3 kHz) with intensity colour coded. By left clicking a location on the spectrogram an image of the nearest sample's spectrogram and its waveform are displayed. The time-stacked spectrograms are useful for easily visualising when major sources are present as the dominant sources have a unique frequency content, so fill certain bands of energy in the spectrograms. For example a section from the Perth Canyon with nearby pygmy blue whale calling is shown on the figure below, with a full pygmy blue whale song type on the left and two days of stacked sea noise on the right.
The National Mooring Network Publication Report. If you have any questions regarding the data, or corrections, or would like to add a publication or presentation that uses IMOS data please contact the IMOS office via email: publication(at)emii.org.au.
Your access to IMOS Acoustic Observatory data discovery and exploration is through the Australian Ocean Data Network (AODN) Portal.
Recommended software packages for processing data are indicated below. If you wish to use either package and it cannot open the IMOS data files please advise us and we will contact the software providers to advise them of the data format. We will provide routines to read the data files if requested. IMOS data has been analysed using Ishmael. Curtin University has a processing package used to easily and quickly assess these data sets (Chorus, which does the same as the web viewer but with more options) and is in the process of releasing this on its website (cmst.curtin.edu.au).