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Passive Acoustic Monitoring

A Passive Acoustic Monitoring (PAM) System is used to passively, detect process and/or record underwater sound using towed or static underwater microphones called hydrophones.

A Passive Acoustic Monitoring (PAM) System is used to passively, detect process and/or record underwater sound using towed or static underwater microphones called hydrophones. Such sounds can include, but are not limited to, the vocalisations of marine mammals, natural ambient noise and man-made (anthropogenic) noise.

Towed Passive Acoustic Monitoring System

Anthropogenic noise from activities such as seismic exploration, pile driving, and rig decommissioning have the potential to be harmful to marine mammals. Industries are therefore often required to put mitigation measures in place when carrying out these activities. Real time acoustic detection of marine mammals using a towed Passive Acoustic Monitoring System (www.towedarray.co.uk) ensures that mitigation guidelines set out by organisations such as the Joint Nature Conservation Committee (JNCC) in the UK and Bureau of Ocean Energy Management (BOEM) in the USA be adhered to at times when Marine Mammal Observers (MMOs, see www.marinemammalobserver.co.uk) are unable to carry out visual watches.

Towed Passive Acoustic Monitoring Systems are used also widely for scientific research on the presence, distribution, seasonal occurrence and behaviour of cetaceans (whales, dolphins and porpoises) around the world.

Components of a Towed Passive Acoustic Monitoring System

A basic towed Passive Acoustic Monitoring System comprises an in-water hydrophone array (one or multiple), depth sensor, deck cable, electronic processing unit, GPS and laptops with detection software such as PAMguard (www.pamguard.org).

When marine mammals emit echolocation (sonar) clicks or other vocalisations, the hydrophone receives these sounds and transmits them through the deck cable to the electronic processing unit. By using different hydrophones and/or sound cards, the Passive Acoustic Monitoring System can be specialised to detect different species of interest for each individual study or survey. High frequency sound cards (17 kHz – 250 kHz) are essential when trying to detect porpoise (Phocoena Phocoena) clicks, as the sound produced is of a higher frequency (ca. 125 kHz). Mid (20 Hz – 20 kHz) and low (1 Hz – 150 Hz) frequency range sound cards are required to detect dolphin whistles or baleen whale vocalisations, respectively.

The signal from the electronic processing unit is fed into a laptop where the Passive Acoustic Monitoring operator (www.pamsystems.co.uk) can view the vocalisations and echolocation clicks on screen. The system is also equipped with headphones, which allows the vocalisations within the human hearing range to be monitored acoustically.

There are a number of software programs available to view the incoming vocal sounds, such as Logger 2000, Whistle, Rainbow Click and Rainbow Click Porpoise; however, the most commonly used program offshore is PAMGUARD (www.pamguard.org). This incorporates elements of all the programs in the form of modules, which can be selected by the Passive Acoustic Monitoring operator to form a configuration specific to their project. This software is the industry standard.

With the use of multiple hydrophone elements, an estimation of distance and location (often with left-right ambiguity) can sometimes be displayed on screen in the form of a radar plot. This is calculated by using the difference in time the sound takes to reach each individual hydrophone element.

Ocean Science Consulting and Towed Passive Acoustic Monitoring Systems

Along with having top of the range equipment available for hire, Ocean Science Consulting Ltd (OSC) can provide fully qualified Passive Acoustic Monitoring operators with the skills, knowledge and certifications required to monitor marine mammals and measure anthropogenic noise offshore. Our extensive background knowledge and experience means we can supply sound scientific advice on the adherence to mitigation guidelines.

Static Passive Acoustic Monitoring System

Static (moored or over-the side) Passive Acoustic Monitoring Systems such as underwater autonomous passive acoustic click detectors (T-PODs www.t-pod.co.uk and C-PODs www.cpodclickdetector.com), are extremely useful when conducting research into the presence of odontocetes (e.g. porpoises and dolphins). Once deployed, they can be left in situ, recording continually for weeks or months at a time, 24 hours a day. This makes them extremely useful when other forms of observation are inadequate, for example at night or during winter months when boat based surveys may be impractical.

Static Passive Acoustic Monitoring Systems are beneficial for species such as harbour porpoise, which are difficult to observe in the wild due to their small size and quiet surface behaviour and beaked whales which spend considerably periods of time at depth.

Within the scientific community T-PODs and C-PODs have been used to conduct research into habitat partitioning between co-existing species and to assess the impact of offshore wind farms on the presence of harbour porpoises. Ocean Science Consulting has used T-PODs and C-PODs around North Sea offshore oil rigs and production platforms to show the importance of these structures as feeding grounds for harbour porpoises. To read more about OSC’s scientific publications, please see www.osc.co.uk.

Components of a Static Passive Acoustic Monitoring System

The T-POD (www.t-podporpoiseclickdetector.co.uk/) and the more recently produced C-POD (www.c-podclickdetector.com) are battery powered Static Passive Acoustic Monitoring Systems that comprise a hydrophone, amplifier, band pass filter and data logger, all enclosed in a waterproof casing that can be attached to a mooring line.

Once deployed, the hydrophone receives the echolocation clicks of odontocetes and logs the time of occurrence, centre frequency, intensity, duration, bandwidth, and frequency trend of the sound onto the memory card. Once the memory card has been retrieved, the data can be uploaded on to a computer and analysed in specialised software known as T-POD.exe or C-POD.exe. This software looks for echolocation click trains and identifies those that match the characteristics of dolphin and porpoise click trains.

Ocean Science Consulting and Static Passive Acoustic Monitoring Systems

One of the key areas of interest for OSC is the previously unknown presence of harbour porpoises around offshore platforms in the North Sea. Ocean Science Consulting has undertaken extensive research using Static Passive Acoustic Monitoring Systems, which puts us in an excellent position to provide expert advice on the utilisation and deployment of C-PODs and T-PODs.

The specialised mooring system used by OSC is so successful that OSC has a 100% recovery rate; OSC has never lost a T-POD or C-POD, even when deployed in a fishing trawling zone for over six months.

Ocean Science Consulting has many different types of Passive Acoustic Monitoring Systems, including T-PODs and C-PODs, available for hire. For more information please refer to our website www.osc.co.uk.

Ocean Science Consulting

Founded in 2004, OSC has been supplying the offshore industry with high quality environmental services that can assist with the initial stages of a project right through to the final report. Services include:

We take great pride in our work and are committed to providing our clients with practical and innovative solutions to their proposals. All our staff members have a minimum of a degree in a marine science (or equivalent), are fully qualified and certified to work offshore, and have round the clock technical and logistical support from land-based experts. For more information about OSC and the services we offer, please refer to our website www.osc.co.uk