Internship Report
Investigation of potential modifications of a passive acoustic monitoring system for a wider commercial use.
Irene Voellmy in partnership with Ultra Electronics Ltd. Investigation of potential modifications of a passive acoustic monitoring (PAM) system for a wider commercial use
NERC MRE knowledge exchange internship report
Irene Voellmy
October 2013 NERC MRE internship report Irene Voellmy
Table of contents
Aim of this internship ...... 3
Part I: Applications of PAM systems ...... 3
1. Research requirements ...... 4
2. Regulation and industry requirements ...... 5
3. Requirements reported by PAM users in the questionnaire ...... 6
4. Implications for Passive Acoustic Monitoring (PAM) devices ...... 15
5. Limitations and gaps of autonomous PAM systems ...... 16
6. Potential of Ultra Electronics sonobuouys to meet requirements and to fill gaps ...... 17
Part II: Detection and classification of marine mammals ...... 19
1. Humpback whales in Madagaskar ...... 20
2. Dolphin clicks and whistles North Carolina ...... 22
3. Ambient noise in Blyth ...... 24
4. Conclusions ...... 26
NERC MRE knowledge exchange internship as a tool to use knowledge acquired by academic research for commercial interests ...... 28
Acknowledgements ...... 29
References...... 30
Appendix 1: Sonobuoy description ...... 32
Appendix 2: SurveyMonkey questionnaire ...... 34
Appendix 3: Marine mammal detector settings ...... 41
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Investigation of potential modifications of a passive acoustic monitoring (PAM) system for a wider commercial use
Aim of this internship
The project aimed to explore potential modifications of a military passive sonar system (SSQ 906G Low frequency analysis and recording (LOFAR) Sonobuoy, Ultra Electronics, Greenford, UK) for wider commercial use as a Passive Acoustic Monitoring (PAM) system, including an automated system to detect, classify and localise (DCL) marine mammals by their emitted sounds. Originally, this system had been developed for deployment from an aircraft to detect quiet submarines during WWII by listening to sounds transmitted by the system (Discovery of Sound in the Sea (DOSITS) 2013; see Appendix 1 for Ultra Electronics LOFAR sonobuoy original description).
The objectives should be achieved by exploring today’s requirements and trends in applications of PAM systems (part I of this report) and by exploring detection programs in use to create a user- friendly software package to record and detect marine mammals in real-time to be added to the modified sonobuoys (part II of this report).
Part I: Applications of PAM systems
Research on marine mammals has increasingly used adapted military passive sonar techniques during the last few decades for marine mammal research and abundance monitoring, as acoustic detection of emitted sounds of marine mammals complement limitations of visual surveys, which can only be made at daylight, in favourable weather conditions based on visual observations of marine mammals during the short time they emerge from the water surface (Zimmer 2011). More recently, potential impacts of anthropogenic (man-made) noise emission have been more and more recognised and described (e.g. Nowacek et al. 2007; Popper & Hastings 2009; Barber et al. 2010). Moreover, the significance of acoustic environment characterisation to assess habitat quality has been discovered, as well as the potential to acoustically monitor changes of species composition and ecosystems induced by human activities (e.g. Blumstein et al. 2011). These developments have diversified PAM applications and will further increase and diversify usage of PAM devices. Today, PAM systems are used in research, noise emission monitoring and regulation by academic institutions, NGOs, policy makers and industry.
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To enable informed decisions about most effective modifications of Ultra Electronic sonobuoys for wider commercial use, I assessed most common applications and future trends of using PAM systems by conducting a short and non-exhaustive literature review as well as by attending a meeting on marine mammal detection and classification in St. Andrews, a conference on underwater acoustics in Corfu, and by participating in the IMARES - TNO Workshop on “International Harmonisation of Approaches to Define Underwater Noise Exposure Criteria” in Budapest to investigate current use and future trends in PAM system applications. In addition, Peter Dobbins and I created an internet-based questionnaire to explore current requirements of regulators, researchers, engineers, and companies using or intending to use PAM systems.
1. Research requirements
PAM is used for a variety of academic and non-academic research fields involving bioacousticians, physicists, conservationists, consultancies, regulators, and industry.
Research includes investigation of acoustic behaviour of marine mammals, reptiles, anurans (frogs and toads), fish and invertebrates, as aquatic animals are very difficult to observe directly, but are acoustically detectable using emitted sounds (e.g. Zimmer 2011). Each species emits its own sounds with sound frequencies ranging from 5 Hz to 140 kHz and thus comes with its own technical requirements, such as the ability to record high frequency sounds with minimum sampling frequency rates of 300 kHz and high data processing capacities, respectively. Moreover, most projects will run for extended time periods of several months, requiring high data storage capacities and efficient data processing and analyses. Consequently, many projects on marine mammals involve automated detection and classification programs, most of which also requiring localisation of vocalising animals for group size and population density estimation (Zimmer 2011).
As it is increasingly recognised that man-made sound can negatively impact aquatic organisms, PAM systems are increasingly used for quantification, characterisation and monitoring anthropogenic noise, and projects investigating effects of human acoustic interference (e.g. Blumstein et al. 2011). In addition to previously mentioned requirements, work on human sound emissions demands a high dynamic range not only to capture low level noises from distant ambient noise, but also high level noises emitted by animals or sounds close to the receiver.
Another fast growing research field is the characterisation of acoustic environments to monitor species presence and composition, to determine criteria indicating high quality habitats as well as to
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monitor changes over time, for instance, changes triggered by human interference (e.g. Blumstein et al. 2011).
It is important to note that many species other than marine mammals detect and rely on particle motion to various extents, rather than on the sound pressure aspect of sound (e.g. Salmon 1971; Goodall et al. 1990; Popper & Fay 2011). Since research on taxa other than marine mammals has intensified substantially over the past decade, there is a need for developing PAMs capable of quantifying particle motion in addition to sound pressure. Integration of particle motion measurements will require simultaneous multichannel recordings, as particle motion is directional within the three dimensional space, consisting of movement components in the x-, y-, and z-axis.
2. Regulation and industry requirements
Regulators and industry use PAM devices for three main purposes: first, to monitor anthropogenic sound emission, such as noise emitted during seismic surveys, construction and operation of marine renewable energy converters, or noise emitted by ship and boat traffic (Lucke et al. In Prep.). Second, PAM devices are used to monitor abundance of marine mammal species in a given habitat, in some projects including investigating change of species composition with human activities (Blumstein et al. 2011). Third, PAM systems can serve as a real-time warning tool to alert vessels to the presence of marine mammals, to minimise or divert ship traffic to different routes, for example, further away from breeding grounds (Silber & Bettridge 2006). Alerting PAM systems could also be used for workers to interrupt or minimise seismic surveys, drilling, pile driving and other noise generating activities while marine mammals are present.
Requirements to monitor anthropogenic noise emission generally overlap with requirements of researchers investigating acoustic environments. Regulations on how to quantify and monitor anthropogenic sound emission, however, are still very vague (De Jong et al. 2011; Lucke et al. In Prep.), as not much is known, for example, for how long a specific area has to be acoustically monitored to quantify and characterise naturally occurring ambient noise and noise levels added to the ambient noise by human activities. This issue is currently further addressed by the NERC MRE internship project by Silvana Neves. Moreover, it is not known which parameters of noise emitted are triggering most impairing effects in animals, for instance, whether the onset of noise and its duration, as well as its predictability is determining effects on aquatic organisms rather than sound levels per se. Specific guidelines and regulations vary substantially between countries (Lucke et al. In Prep.). As a result specific requirements will differ between countries on how human activities are
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surveyed, even though several working groups are currently working on harmonisation and standardisation of monitoring protocols (see Ainslie 2011; De Jong et al. 2011; Lucke et al. In Prep. for examples).
However, trends for future requirements became apparent at the IMARES-TNO workshop in Budapest, August 2013: regulators are becoming increasingly aware of the necessity of including sound measurements relevant for non-marine mammals (see above). Thus, integrating measurements of particle motion and recording on multiple channels simultaneously will become increasingly important for regulators and industry. Moreover, sound quantification at different depths, as well as including hydrophones sensitive to different frequency ranges, and sound source localisation will become iimportant to assess sound exposures of aquatic organisms.
With increasing numbers of offshore marine renewable energy devices, the number of projects monitoring sound emission in shallow waters will rise as a consequence. Sound propagation patterns in shallow waters are more complicated and thus more difficult to predict. PAM devices may become increasingly important for empirical verification and refinements of theoretical sound propagation models to improve estimation of the extent marine organisms are exposed to anthropogenic noise emission. Data loggers recording non-acoustic data, such as water temperature and salinity, will be important to improve sound propagation calculations. Recording additional data on water quality, such as turbidity, acidity and other chemical parameters will also allow a more integrative approach taking into account potentially confounding and synergistic effects, for example, potential effects of bad water quality on animal sound production in addition to increased ambient noise levels.
Using PAM systems to monitor marine mammal abundance, as well as using real-time PAM techniques as a warning system to manage human activity, will require similar specifications to marine mammal research, however, additional automated and robust detection and classification algorithms that are easily operable by non-specialists will be desirable.
3. Requirements reported by PAM users in the questionnaire
A web-based questionnaire was composed in SurveyMonkey (www.surveymonkey.com) to investigate further and verify the current state of the art of how PAM systems are used, as well as specific features sonobuoys need to provide. The questionnaire consisted of a total of eight questions addressing PAM user’s institutions and working areas, their areas of interest and
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requirements sonobuoys need to meet (Appendix 2). The questionnaire was distributed through mailing lists (Bioacoustics List (Cornell University), International Bioacoustics Council, Marine Mammals Research and Conservation Discussion (MARMAM), Coral List) and sent by email to specific contacts to reach as many PAM users from as many diverse application fields as possible, including physicists, bioacousticians, regulators, PAM providers, consultancies, military and commercial institutions, etc.
A total of 74 PAM users responded to the questionnaire. The majority and almost half of PAM users answering the questionnaire worked for an academic institution (table 1, fig. 1), while many fewer users are PAM service providers or researchers funded by the government. Six PAM users work in a commercial research organisation, and only 3 users are funded independently (table 1, fig. 1). Two users work for the oil and gas industry, consultancies and NGOs, respectively (table 1, fig. 1). One person is working for the renewable energy section and one person for an aquarium (table 1, fig. 1). Although sonobuoys were originally developed for military purposes (Zimmer 2011), none of the users responding to the questionnaire was working for a military institution. There were also none using PAM devices for whale watching tours, outreach activities or as a regulatory organisation. It is possible that the email contacts and mailing lists we have used did not reach representatives of these sections.
Table 1. Number and percentage of PAM users and their respective organisations and working areas (n = 74).
Organisation/working area Number of PAM users Percentage of PAM users
Academic institution 33 44.6 PAM service provider 13 17.6 Government research organisation 11 14.9 Commercial research organisation 6 8.1 Independent research 3 4.1 Oil and gas industry 2 2.7 Consultancy 2 2.7 NGO 2 2.7 Renewable energy organisation 1 1.4 Aquarium 1 1.4
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Academic institution
PAM service provider
Government research organisation
Commercial research organisation
Independent research
NGO
Consultancy
Oil and gas industry
Aquarium
Renewable energy organisation
0 10 20 30 40 50 % PAM users
Figure 1. PAM users and their institutions or work areas (in percentage; n = 74).
The majority of PAM users operate 2 to 5 devices (29 of 71; 40.8%), while 19 of 71 users (26.8%) operate 10 or more devices, and 10 of 71 users own 6 – 10 PAM devices (14.1%; fig. 2). However, there are also 13 of 71 PAM users working with one PAM device only (18,3%; fig. 2).
1
2-5
6-10
10 +
0 10 20 30 40 50 % PAM users
Figure 2. Number of PAM devices used by PAM users (n = 71).
Most PAM devices were used to collect long term data with collecting periods exceeding a year (20 of 72 PAM users; 27.8%; fig. 3), or 9 months to a year (18 of 72 PAM users; 25.0%; fig. 3). Only 2 PAM users collected acoustic data for less than a week (2.8%; fig. 3).
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less than a week
week to a month
1-3 months
3-6 months
6-9 months
9 months to a year
more than a year
0 5 10 15 20 25 30 % PAM users
Figure 3. Time period PAM users collect data (n = 71).
Most PAM users are involved in projects focusing on marine mammal sounds (59 of 70; 84.3%; fig. 4) and anthropogenic noise (53 of 70; 75.7%; fig. 4). Most PAM projects address multiple topics (57 of 70; 81.4%). This is not surprising, as many of these interests also require investigation of other related areas, such as monitoring and assessing impacts of anthropogenic noise requires monitoring naturally occurring ambient noise, as well as monitoring aquatic organism presence and abundance.
Marine mammal sounds
other aquatic organism sounds
Bird monitoring
Anuran monitoring
Seismic noise
Other natural abiotic noise
Anthropogenic noise
Acoustic environment/soundscape
Sound propagation model evaluation
0 10 20 30 40 50 60 70 80 90
% PAM users Figure 4. PAM user’s areas of interests (n = 70).
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PAM users monitor a wide range of marine mammals (table 5, fig. 5). However, the majority focuses on cetaceans, and fewer monitor pinnipeds, of which the vast majority of projects seem to focus on species of the Northern hemisphere (table 5, fig. 5). Only one PAM device user reported to monitor Dugongs (table 5, fig.5).
Table 5. Species of interest for PAM users (n = 60)
Species of interest Number of users Percentage of users Porpoises 31 51.7 Oceanic Dolphins 35 58.3 River Dolphins 7 11.7 Orcas 24 40.0 Sperm Whales 32 53.3 Beaked Whales 28 46.7 Belugas and Narwhals 14 23.3 other odontocetes 10 16.7 Right and Bowhead Whales 25 41.7 Rorquals 57 95.0 Dugong 1 1.7 Arctic pinnipeds 32 53.3 Antarctic pinnipeds 3 5.0
Porpoises
Oceanic Dolphins
River Dolphins
Orcas
Sperm Whales
Beaked Whales
Belugas and Narwhals
other odontecetes
Right and Bowhead Whales
Rorquals
Dugong
Arctic pinnipeds
Antarctic pinnipeds
0 10 20 30 40 50 60 70 80 90 100 % PAM users
Figure 5. Species of interest for PAM users (n = 60)
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For most PAM device users, it is important that sonobuoys are recoverable and reusable with a rechargeable battery to avoid littering the coast or seabed using one-way PAM devices, as is the case for most sonobuoys developed for military purposes (table 6, fig.6). Most PAM users would like to locate sonobuoys using GPS (table 6, fig.6). One user also suggested an AIS (Automatic Identification System) transmission system on board and another suggested increasing visibility and locatability using an acoustic pinger or a flashing light to increase the chance of retrieving sonobuoys. Three quarters of PAM users answering the questionnaire record sound up to 20kHz, but almost 60% also record up to 150 kHz to include marine mammals emitting ultrasonic sound, such as porpoise or dolphin clicks. The majority of PAM users would also prefer on-board hard disk recording of full bandwith signals for ultrasonic recordings (table 6, fig.6). Less important, but still regarded as preferable by most PAM users, are small lightweight sonobuoys which can be deployed by one person from a small boat (table 6, fig.6). There seems to no clear-cut preference of specific hydrophone depths, as some PAM users record acoustic data near the shoreline, while some use their sonobuoys in the open and deep ocean (table 6, fig.6). The same seems true for directional hydrophones, as most localisations are achieved using PAM arrays, not by directional hydrophones from a single PAM device (table 6, fig.6). Radio telemetry does not seem essential for many PAM users, as not all users need real-time data monitoring, and PAM users recording ultrasound will have to use wireless data transfer facilities (table 6, fig.6). In contrast to supposed future trends to integrate non-acoustic data to allow for a more holistic approach, most users classify data loggers collecting additional non-acoustic data about water quality as not essential. Similarly, even though particle motion quantifications and measurements at different depths using different hydrophones seem to become increasingly important and high numbers of simultaneous radio channels does not seem a widespread requirement (table 6, fig.6). However, most devices used to date are either not collecting real-time data (e.g. devices by Wildlife Acoustics Inc., Concord, MA, USA), or transmit data by wireless internet connections, instead of radio channels (e.g. devices by RTsys, Caudan, France).
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Table 6. Interest of PAM users in specific hardware specifications. “Yes” denotes specifications essential for user’s to meet their requirements, “not essential” denotes specifications helpful for additional or future data collection, but not essential for fulfilling projects, “no” denotes specifications not necessary for users.
Proposed hardware specifications Total Yes (%) Not essential No (%) answers (%) Recoverable, reusable, rechargeable battery 50 78.0 16.0 6.0 HiFi quality signal 10Hz – 20kHz 49 75.5 16.3 8.2 Hydrophone suspension to minimise recording noise 48 70.8 20.8 8.3 GPS/compass positioning 50 68.0 26.0 6.0 On-board full bandwidth backup recording 50 64.0 30.0 6.0 Compressed signal 10kHz – 150kHz 50 58.0 24.0 18.0 Small, lightweight for hand deployment 50 56.0 40.0 4.0 Hydrophone depth selectable 15/30/60 m 48 45.8 33.3 20.8 FM radio telemetry 48 45.8 29.2 25.0 Maximum depth more than 60 m 47 42.6 31.9 25.5 Directional hydrophones 50 42.0 42.0 16.0 Maximum depth more than 300 m 49 40.8 30.6 28.6 Data logger recording temperature, salinity, pH 49 36.7 53.1 10.2 Up to 100 selectable independent transmission channels 49 16.3 46.9 36.7
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Recoverable, reusable, rechargeable battery
HiFi quality signal 10Hz – 20kHz
Hydrophone suspension to minimise recording noise
GPS/compass positioning
On-board full bandwidth backup recording
Compressed signal 10kHz – 150kHz
Small, lightweight for hand deployment
Hydrophone depth selectable 15/30/60 m Yes
FM radio telemetry Not essential No Maximum depth more than 60 m
Directional hydrophones
Maximum depth more than 300 m
Data logger recording temperature, salinity, pH Up to 100 selectable independent transmission channels
0 10 20 30 40 50 60 70 80 %
Figure 6. Interest of PAM users in specific hardware specifications. “Yes” denotes specifications essential for user’s to meet their requirements, “not essential” denotes specifications helpful for additional or future data collection, but not essential for fulfilling projects, “no” denotes specifications not necessary for users.
Over 75% of PAM users would prefer devices with adjustable recording levels to meet the requirements of wide dynamic range to record very quiet ambient sounds, but also much louder sounds, such as noise emitted by pile driving activities or ship traffic. However, only some users indicate they would need an interactive device control to change settings during recording sessions (table 7). Also, the majority of users would like to monitor acoustic data in real-time, but not only rely on recording data via data transfer but also have an on-board hard-disk in addition to ensure back-up data storage (table 7). Some users also commented on the fragility of real-time data transmission using radio signals or a wireless connection, causing data losses. For most applications,
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3D sound source localisation will be required, preferably using a single buoy (table 7). Most users will also need real-time detection and classification of marine mammals for their applications. Some would require an alerting function included when marine mammal sounds are detected, but only some would need these detections displayed (table 7). However, one PAM device user commented that they would prefer open source software rather than getting black boxes of ready-to-use detection programs delivered by the PAM system provider, which they expect to be more difficult to control and adjust in case of suboptimal detection performance.
Some PAM device users pointed out that the main problems to be solved by PAM device software are the decreasing computer efficiency caused by the large quantity of data generated and associated increasing system instabilities. This is especially the case when working with ultrasonic sounds. Moreover, PAM devices come with high costs. PAM users also reported problems to detect low frequency calls using towed arrays or in presence of low frequency anthropogenic noise.
Table 7. Interest of PAM users in specific software and receiver specifications. “Yes” denotes specifications essential for user’s to meet their requirements, “not essential” denotes specifications helpful for additional or future data collection, but not essential for fulfilling projects, “no” denotes specifications not necessary for users.
Specifications for the receiver/software Total Yes Not No (%) answers (%) essential (%) Adjustable recording levels 49 77.6 22.4 0.0 Direct data transfer and back-up on hard disk 50 68.0 30.0 2.0 Localisation in range, bearing and depth 49 65.3 28.6 6.1 Real-time displays of signal waveforms, spectra and 49 59.2 32.7 8.2 spectrograms
In-built detection algorithms of marine mammal 49 59.2 28.6 12.2 vocalisations
In-built marine mammal species identification in addition 49 59.2 30.6 10.2 to detection Bearing localisation with single buoy 49 59.2 30.6 10.2 Programmable alerts for presence of cetaceans 49 53.1 34.7 12.2 Choice of single or multi-channel (up to 8) FM receiver 50 52.0 42.0 6.0 Interactive device control 48 45.8 47.9 6.3 Plan and waterfall displays for detections 49 36.7 51.0 12.2
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Adjustable recording levels
direct data transfer and back-up on hard disk
Localisation in range, bearing and depth
Bearing localisation with single buoy
In-built marine mammal species identification in addition to detection In-built detection algorithms of marine mammal vocalisations Real-time displays of signal waveforms, spectra and spectrograms
Programmable alerts for presence of cetaceans
Choice of single or multi-channel (up to 8) FM receiver Yes
Interactive device control Not essential
No Plan and waterfall displays for detections
0 10 20 30 40 50 60 70 80 %
Figure 7. Interest of PAM users in specific software and receiver specifications. “Yes” denotes specifications essential for user’s to meet their requirements, “not essential” denotes specifications helpful for additional or future data collection, but not essential for fulfilling projects, “no” denotes specifications not necessary for users.
4. Implications for Passive Acoustic Monitoring (PAM) devices
The above examples and the questionnaire illustrate that there is a wide range of potential requirements and purposes PAM devices are used. The questionnaire indicates that the majority of PAM device users currently uses 2 - 5 PAM devices to collect long-term data of a year and longer, to monitor marine mammal and anthropogenic sounds. In general, PAM devices will need to include a high dynamic range, the capability to record data on multiple channels continuously for an extended period of time including high data storage capacities. These tasks should preferably be met in a highly cost effective, data processing and storage-effective way. Moreover, the majority of users
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prefer retrievable devices with rechargeable batteries to meet requirements of long-term data collection and to minimise littering the seabed.
Many users work with computer software detecting and classifying marine mammals to facilitate analysis of long-term data. However, not all users monitoring marine mammals would accept an in- built software device, as some prefer data post-processing to real-time monitoring and open source software to avoid the black-box nature of ready-to-use software with limited control over detection algorithms. This is especially true for research projects. However, some projects will require real- time monitoring, for instance, projects using PAM systems as warning devices to stop drilling/pile driving or to divert ship traffic in presence of marine mammals. This application can be highly demanding, as many marine mammals, such as Humpback whales (Megaptera novaeangliae) and Bottlenose dolphins (Tursiops truncatus) emit highly variable sounds and thus are difficult to detect and classify by detection programs robust enough to be operated by non-bioacousticians.
Almost 78% of PAM users would prefer devices offering adjustable recording levels to increase dynamic range, as not only quiet ambient noise is of interest, but also sounds emitted by human activities. PAM users seem to operate their devices at many different depths, thus, hydrophone depths may best be tailored to specific customer needs.
Research focusing on soundscapes and sounds emitted by animals other than marine mammals is increasing. Thus, the use of sonobuoys will diversify resulting in more diverse applications and requirements leading beyond sound pressure measurements, marine mammal detection, identification and localisation towards multichannel devices integrating different acoustic measurements including particle motion and sound pressure measurements at different depths and sound frequency ranges.
5. Limitations and gaps of autonomous PAM systems
PAM systems, such as sonobuoys, are autonomous recording devices. Thus, power supply and space is inherently limited, restricting processing power and data storage capacity (Zimmer 2011). These limitations become especially crucial when data collection is required for high frequency sample rates for periods of several months to exceeding a year.
In case real-time data processing is necessary, data transfer is only possible when the sending element is located above the water surface. However, this will increase the vulnerability of the
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system, for example, to overrunning ships or by hydrodynamic forces ripping the system apart (Zimmer 2011).
Many stationary autonomous PAM devices do not allow for real-time monitoring of the recordings, and this does not make available system control checks or adjustments of recording levels. In addition, in case of monitoring presence/absence of marine mammal during pile driving or certain ship movements, it is not possible to control human activity according to animal movements.
Some autonomous PAM devices offering real-time data monitoring do not allow for a two-way communication, for example, PAM systems using radio transmission to transfer data. The possibility for a two-way communication would allow for adjusting and controlling recording levels during recordings to increase dynamic ranges, for example to adjust for very quiet ambient noise interrupted by very loud ship passages.
As outlined in section 1, the increasing focus on non-marine mammals will lead to the necessity to integrate particle motion in the future; however, none of the current systems offer this option. This is partly the case because accelerometers have not yet been developed in a more widely available commercial scope, possibly because the need is only becoming more widely recognised by policy makers and regulators.
6. Potential of Ultra Electronics sonobuouys to meet requirements and to fill gaps
The Ultra Electronics sonobuoys are light-weight, and thus easy to transport and deploy. The system is equipped with a surface floater allowing for real-time data transmission and monitoring. As the sonobuoy is designed to drift freely with the water current, and the hydrophone is connected to the sonobuoy by a coiled, low self-noise cable, the system allows for low self-noise recordings of low level ambient noise at low depths. To increase the dynamic range, an additional filter is added to the recording system (pre-whitening) reducing lower frequency sounds while boosting higher frequency signals, as most sound energy in aquatic ambient noise is located in low frequency ranges, due to water currents and anthropogenic noise, such as ship noise.
In addition to the above features, Ultra Electronics sonobuoys have a lot of potential to meet further requirements by research and conservation by relatively simple modifications:
The increasing necessity of long-term ambient noise and anthropogenic noise assessments at growing numbers of locations, the design of retrievable and reusable sonobuoys become
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mandatory. Many researchers monitoring marine mammals switched to reusable solutions to avoid littering the coast with one-way use sonobuoys containing lithium batteries, among other non- biodegradable substances (Danielle Harris, personal communication). In order to facilitate sonobuoy recollection, floaters could be designed to become more visible, as well as equipped with a GPS locator. Information of current positions of the PAM device will become increasingly important as with increasing floating time, the position will be substantially altered from the original deployment site. Increasing floating time on the surface would also increase the probability to become overrun by a ship. More visible floaters, possibly equipped with a flashing light or AIS signals, detectable from approaching vessels, would also help to avoid collisions (Zimmer 2011), although environmental effects of a flashing light need to be assessed thoroughly before integrating it in the system, as light is reported to attract or disrupt the behaviour of many animals, including aquatic organisms (e.g. Doherty 1987; Longcore & Rich 2004).
Retrievability and reusability would also provide the possibility to add a hard disc for back up data storage in cases real-time transmission of data is impossible or interrupted. For extended use, solar panels could be mounted on the floating part of the system to increase power supply, an inert limitation of autonomous PAM systems.
Replacing radio transmission by wireless internet transmission would allow transferring higher data loads, such as recordings of frequency levels higher than 15 kHz, the current limit for radio transmitted signals. This will become necessary if adapting the system to monitoring marine mammals or other animals emitting high frequency sounds. Harbour porpoises, for example, emit sounds up to 140 kHz (Au 1993) and are abundant around the British coast (Northridge et al. 1995; Shirihai 2006), where many marine renewable energy devices are planned. Transfer of high data loads is also necessary when simultaneously transmitting signals of several hydrophones at different depths or spatial locations, etc. Moreover, simultaneous multichannel data transmission will become mandatory with the integration of particle motion measurements.
Wireless data transmission would also allow for a two-way communication, and thus increase controllability of sonobuoy recordings. Dynamic ranges could thus be further increased by additional adjustability of recording levels, etc.
To increase flexibility of sonobuoys, modifying its case would allow inclusion of multiple connectors for the recording system to include hydrophones sensitive to high frequency and hydrophones sensitive to low frequency signals at the same time, as well as hydrophones at different depths, or directional hydrophones. Collection of additional data, such as data loggers recording non-acoustic
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data to allow for a more holistic approach of acoustic monitoring projects (see above), and particle motion in addition to sound pressure measurements will become mandatory with the development of new accelerometers and the increasing interest in non marine mammal species and with it, the integration of three additional, simultaneous recording channels.
Part II: Detection and classification of marine mammals
We tested two well-developed marine mammal detection programs, PAMGUARD v1.12.05 BETA (Gillespie et al. 2009) and Marine Mammal Acoustic Detector (MMAD; trial version 3-2 WAV; Kaon Ltd. , Guildford, UK) using audio files of:
(1) Humpback whale songs (Megaptera novaeangliae) recorded in Madagascar by Federica Pace in July 2011, using a SSQ 906G LOFAR Sonobuoy (Ultra Electronics, Greenford, UK). Acoustic signals were radio transmitted using WiNRADiO G 305 v2.22 (20013 WiNRADiO Communications, RADIXON UK Ltd, Chesterfield, UK) and recorded to a laptop computer (Dell Latitude (Dell Corporation Limited, Bracknell, UK) using Audacity v1.3.13 (1999-2011 Audacity Team; SourceForge.net)
(2) Bottlenose dolphin whistles (Tursiops truncatus) and clicks recorded in Onslow Bay, North Carolina (33°46.081'N, 76°27.598'W) by Lynne Williams Hodge and Andy Read in January 2008 during a project funded by Naval Facilities Engineering Command Atlantic (Williams Hodge 2011). Unfiltered recordings were made using a towed 4-element hydrophone array with 300 m tow cables (Seiche Measurements Ltd, Bradworthy, UK) with a flat frequency response (+/- 3 dB) between 2 and 100 kHz, sensitivity -165 dB re 1 V/µPA), connected to a MOTU Traveler audio interface (Mark of the Unicorn, Cambridge,MA, USA), and a laptop using Ishmael (Mellinger 2001). The hydrophone array was towed 150 m behind the vessel at an approximate speed of 16.7 km/h.
(3) Ambient noise recorded by the author in Blyth in July 2013 (55°11.322'N / 1°27.799'W), in an area for which an offshore wind farm is planned for 2014/2015. Recordings were made using a SSQ 906G LOFAR Sonobuoy (Ultra Electronics, Greenford, UK). Acoustic signals were radio transmitted using WiNRADiO G 305 v2.22 (20013 WiNRADiO Communications, RADIXON UK Ltd, Chesterfield, UK) and recorded to a laptop computer (Toshiba Tecra M11-17V (Toshiba Information Systems UK Limited, Weybridge, UK) using Audacity v2.0.3 (1999-2013 Audacity Team; SourceForge.net). Recordings made by sonobuoys were pre-filtered decreasing low frequency sound levels and enhancing high frequency sound levels to increase dynamic range (see above). Thus, for sound files recorded by sonobuoys (the humpback recordings and the ambient noise recordings from Blyth),
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detection performance of the two detection programs was compared using untreated files and files after restoring original sound levels at the test sites using a inverse filter in Adobe Audition 1.5 (© 1992-2004 Adobe Systems Incorporated).
The development of PAMGUARD by experienced PAM users and marine mammal researchers in the UK and the USA (coordinated by Douglas Gillespie) has been funded by the oil and gas industry since 2004 (www.pamguard.org). PAMGUARD is an open access software. The purpose of the software was to provide a worldwide standard detection, localisation and classification program to improve acoustic monitoring techniques of marine mammals for research, regulation and mitigation procedures. The software is organised in modules which can be combined and further developed for specific needs. For testing the software, I used a moan detector to detect low frequency calls of baleen whales, combined with a sperm whale and dolphin detector to detect dolphin whistles and a click detector to detect clicks (see Appendix 3 for exact parameter settings). All three detectors were run simultaneously for all test files to use it as a universal detection program for baleen whales and odontocetes.
MMAD (Marine Mammal Acoustic Detector) is a commercially available software package developed by KAON (www.kaon.co.uk/mmad.asp) to provide easy to use software for industrial purposes, which does not require specific expertise to operate. The software is developed to raise alarms when marine mammal sounds are detected that human activities can be modified accordingly, for example, to interrupt pile driving when marine mammals are present.
1. Humpback whales in Madagaskar
PAMGUARD
In general, PAMGUARD algorithms detected the majority of humpback calls (over 70% in both files, table 8). Undetected calls were either relatively short, thus shorter than specified in the moan detector (Appendix 3), or they consisted of none or very few harmonic structures, thus sound was not connected as much as specified. The number of missed detections could be minimised by modifying parameter specifications to enable detection of shorter and less harmonic calls, however, false positive detection rates would increase as a consequence, especially in the presence of ship noise with signatures containing harmonic elements. Since all undetected calls were emitted as elements within songs lasting for several minutes, missed calls did not result in a failure to detect humpback presence. False positive detection rates were very low for files containing humpback
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songs (table 8), but could be as high as 4 detections/minute in file 2, a recording lacking humpback calls. False positive detections were recorded by both, the moan and whistle detectors (Appendix 3). There was no difference between original recordings and inverse-filtered audio files.
The click detector recorded a very high number of clicks (up to 2590/minute, table 8), even though the audio files tested did not contain any marine mammal clicks. The click detector mainly identifies sudden occurrence of sound, which can easily resemble random ambient noise, even though a high pass filter was used to exclude click detections outside dolphin click frequency ranges (Appendix 3). Thus, a visual inspection of the spectrogram is mandatory to verify any indicated click detections. There was no qualitative difference in the numbers of click detections between untreated, original recordings and inverse-filtered recordings (table 8).
Table 8. Detection results in PAMGUARD.
Sound files File Total calls Correctly Missed calls False positive Clicks duration detected detections (calls) detected File 1 original 3:17.093 147 128 19 2 7905 (87.1%) (12.9%) (1.4%)
filtered 3:17.093 147 128 19 1 7329 (87.1%) (12.9%) (0.7%)
File 2 original 22:46.84 0 n/A n/A 68 24164 1 filtered 22:46.84 0 n/A n/A 80 24151 1 File 3 original 20:00.00 940 674 266 2 51772 0 (71.7%) (28.3%) (0.2%) filtered 20:00.00 940 674 266 1 51799 0 (71.7%) (28.3%) (0.1%)
MMAD
MMAD classified some of the detected humpback moans as calls of Minke whales. Minke whale call features can resemble humpback calls, especially because of the high variability and diversity of humpback calls. In our case, using less specific species classifications may be preferable, such as “low frequency mysticete/baleen whale calls”. If species identification is necessary in a given project, the program may need to be updated with humpback song samples and other marine mammal sounds recorded at the project sites will be conducted prior to using it as an identification tool.
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Warning lag times could be less than a minute, however, in one test file, lag time duration was longer than two minutes in the original audio file, but a warning message already occurred within the first minutes in the reverse filtered test file. In file 1, in contrast, lag times were lower in the original audio file (table 9). Thus, more files need to be tested to determine whether inverse-filtering the audio files prior to running it through the MMAD detection and classification program would improve or negatively affect results. Similar to PAMGUARD, MMAD also produced false positive detections for file 2, in which no marine mammal songs and clicks occurred (table 9). For audio file 2, more false detections were reported by the program for the inverse filtered file than for the untreated original file (table 9).
Table 9. Detection results in MMAD
Sound files HF Minke Delphinid Delphinid Odontocete unclassified Warning Mysticete whale clicking whistles Sperm / lagtime Bottlenose Whale File 1 original 1 2 1 0 0 0 0:00 filtered 1 2 2 0 0 0 0:21 File 2 original 1 16 14 0 0 0 n/A filtered 1 32 30 0 1 0 n/A File 3 original 1 13 13 0 0 0 2:21 filtered 1 13 14 2 0 0 0:21
2. Dolphin clicks and whistles North Carolina
PAMGUARD
For dolphin whistles, detection rates are similar to the ones for humpback calls. The lowest detection rate was 66.7% (table 10), which was lower than detection rates of humpback calls (71.7%; table 8). In all files, presence of whistling dolphins could be detected, however, some call sequences were completely missed, as dolphins emit whistles in short sequences only. This is unlike song sequences in humpback whales, which can last for up to 30 min (Payne & McVay 1971). All files showed a relatively low signal to noise ratio. Moreover, signals were more distorted than humpback calls, resulting in interrupted signals more difficult to detect. Signals were most likely more distorted not only by the generally high ambient noise levels, and potentially longer recording distances, but
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also by the fact that higher frequencies degrade more quickly with distance than lower frequencies (Au & Hastings 2008). Detection rate could only be improved by shortening the duration; acoustic signals need to be correlated between spectrogram windows, in contrast to moan detector settings (Appendix 3). Consequently, frequency ranges were restricted to 3 kHz to 20 kHz to minimise false positive detections caused by passing ships, which can contain harmonic low frequency elements in their noise signature. In spite of these restrictions in the dolphin whistle detector settings, they still resulted in relatively high numbers of false positive detections in test files recorded in Blyth, which did not contain any marine mammals (see below, table 12).
PAMGUARD click detector algorithms also detected a high rate of Dolphin clicks. However, unlike moan and whistle detections, determining numbers of false positive and missed detections is not as straightforward, as click detections are not indicated in the spectrogram by the program, and log files record detection times according to the time clicks were detected by the computer, which do not correspond to the actual file duration.
Table 10: detection results in PAMGUARD
Sound files File Total calls Correctly Missed False Clicks duration detected calls positive detected detections PeterUSWTR-070923- 3:22.280 105 77 28 0 1743 (73.3%) (26.7%) 115637 (3) PeterUSWTR-070923- 10:00.000 127 108 19 1 7473 (85.0%) (15.0%) (0.8%) 120000 (3) PeterUSWTR-071017- 2:21.168 48 32 16 1 1417 (66.7%) (33.3%) (2.1%) 132000 (2) PeterUSWTR-071112- 10:00.000 206 181 25 2 9636 (87.9%) (12.1%) (1.0%) 113000 (4)
MMAD
In three of four files, dolphin whistles and clicks were correctly detected (table 11). In one file, no dolphin whistles and clicks were detected (table 11). Most likely, signal to noise ratio was too low and the test file too short to allow the program to detect whistles and clicks at a confidence level of
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50%, which is the set threshold for the MMAD program to log it as a detection, as single detections are not reported. Thus, potential single detections could not be verified and evaluated.
Similar to the test files of humpback songs, classification seems a bit vague and misleading, as there were no sperm whales (Physeter macrocephalus) and bottlenose whales (Hyperoodon sp.) present. For these recordings as well, it would be preferable to report “odontocetes detected” instead.
Table 11. Detection results in MMAD
Sound files HF Minke Delphinid Delphinid Odontocete unclassified Warning Mysticete whale whistles clicking Sperm / lagtime Bottlenose Whale PeterUSWTR- 0 0 2 2 0 0 0:00 070923-115637 (3) PeterUSWTR- 0 0 5 4 3 2 0:20 070923-120000 (3) PeterUSWTR- 0 0 0 0 0 0 n/A 071017-132000 (2) PeterUSWTR- 0 0 3 1 2 0 4:18 071112-113000 (4)
3. Ambient noise in Blyth
In test files 1 and 2, recordings have been tested in areas with marine mammals present in most of the files. However, we also intended to test false positive detection rates in recordings of areas and during times in which no vocalising marine mammals have been recorded. Thus, ambient noise files recorded in Blyth were included in our analyses.
PAMGUARD
PAMGUARD algorithms detected relatively high numbers of moans and whistles, and very high numbers of clicks (table 12). Moans were more often detected in the presence of ship noise, as some harmonic elements of the ship noise signatures meet the criteria of correlated spectrogram
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windows as specified by the moan detector. Thus, verifications by trained staff will be mandatory before human activities are shut down or modified in case of using the device as a warning tool for marine mammal presence. In case of using PAM devices for research purposes, parameters can be adjusted to meet specific detection requirements, or additional detectors can be built in to be used for specific audio file sequences. Most false positive detections were clicks. Clicks were most likely detected because of regular occurrence of short mechanical noise of water banging against the research vessel’s hull, noises emitted by invertebrates and/or escaping gas bubbles from the seabed, and other sudden and short noise outbursts of ambient noises. This was still the case after filtering out low frequency noises (Appendix 3), as most of these sounds were broadband, as well. As in audio files recorded in Madagascar, reverse-filtering original recordings resulted in slightly lower, but not qualitatively different detection rates.
Table 12. Detection results in PAMGUARD
Sound files File moan and Sperm wales Total detections Click duration whistle and dolphins (without clicks) detector detector detector 3 July 14:20 original 29:26.073 101 0 101 23049 filtered 29:26.073 97 0 97 23055 3 July 14:46 original 23:55.078 75 2 77 11907 filtered 23:55.078 69 2 71 11905 3 July 15:10 original 22:56.561 42 25 67 9830 filtered 22:56.561 33 26 59 9815 3 July 15:43 original 32:12.447 7 0 7 6247 filtered 32:12.447 5 0 5 6248
3 July 16:10 original 25:47.709 2 29 31 11267 filtered 25:47.709 3 29 32 11268 3 July 16:40 original 22:00.000 0 13 13 5403 filtered 22:00.000 0 13 13 5397
MMAD
MMAD did correctly detect no marine mammal sounds in three of six audio files tested in Blyth (table 13). In the three remaining test files, however, different types of marine mammal sounds were still detected, ranging from moans to clicks. This is especially apparent in the first two test files, corresponding to the first 30 minutes of recordings in Blyth, during which the research vessel
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remained stationary with motors switched off and moved away from the sonobuoy during the following 30 minutes. Thus, ship noise artefacts of waves hitting the ship’s hull, as well as the ship motor driving away from the sonobuoy more closely matched detection parameters than the naturally occurring ambient noise dominating recordings made after the first hour the sonobuoy was deployed from the boat. This pattern is also replicated by PAMGUARD detections declining with time after sonobuoy deployment.
Filtering sonobuoy recordings to get original frequency distributions did not minimise false positive detection substantially in the three files marine mammal sounds were detected (table 13).
Table 13. Detection results in MMAD. Green cells indicate files for which correctly no marine mammal calls were detected.
Sound files Minke detected Delphinid clicking Odontocete Sperm / unclassified and duration Bottlenose Whale 3 July 14:20 original 1 5 2 1
29:26.073 filtered 2 5 5 2 3 July 14:46 original 3 2 0 1 23:55.078 filtered 3 2 0 1 3 July 15:10 original 0 0 0 0 22:56.561 filtered 0 0 0 0 3 July 15:43 original 0 0 0 0 32:12.447 filtered 0 0 0 0 3 July 16:10 original 0 0 0 0 25:47.709 filtered 0 0 0 0 3 July 16:40 original 0 0 3 0 22:00.000 filtered 0 0 2 0
4. Conclusions
In general, both detection programs fulfilled their purpose to detect different types of marine mammal calls, ranging from long, harmonic low frequency moans to higher frequency whistles and short, sudden noise pulses in clicks. In all files, except for one file of a duration of 2:21 minutes by MMAD, the programs correctly detected the presence of marine mammal sounds. Thus, it is important to allow for enough assessment time before human activities in question are executed.
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Missed detections of humpback calls in PAMGUARD mainly concerned shorter calls or less harmonic calls, which were elements embedded in a song sequence. Thus, not detecting the presence of humpback whales by missed detections of shorter and less harmonic calls is unlikely. However, if dolphin whistles are missed, which was the case when distorted and occurring in low signal to noise ratio, dolphin presence will more likely remain undetected, as dolphin whistles are emitted in much shorter sequences with longer silent periods in between sequences (see above). Thus, especially in high levels of ambient noise and if calls are highly distorted, the probability to miss dolphin presence will increase. PAMGUARD detections seemed more sensitive than MMAD, as none of the files containing marine mammal calls were undetected. However, KAON’s MMAD has been developed as a warning tool, informing workers and shipping staff of the presence of marine mammals to adjust human activities. Thus, detections are only reported in log files after reaching a predefined threshold of certainty, which has been set at 50%, and has to reach 70% certainty to elicit a warning signal on the screen. Thus, an assessment time of 2:21 minutes may not have been enough to allow the program to detect sufficient numbers of recurring whistles to elicit a warning. Thus, optimal certainty levels and minimum monitoring time before starting pile driving or drilling have to be assessed prior to use it as a warning or detection system. However, as the program does not record single detections in the log file and does not indicate detections in spectrograms, it is difficult to determine causes for false positive or negative detections and thus evaluate optimal detection settings.
The high number of click detections in PAMGUARD can be reduced by adding a click train identifier and spatial information by using sonobuoy arrays with GPS localisers attached. This additional information allows discrimination between random sudden noises, invertebrate clicks and moving marine mammals. MMAD also detected marine mammal clicks in files which did not contain any, however, algorithms and parameters for click detections are not declared, and thus, it is not clear whether additional temporal or spatial information would increase detection precision. Evaluation of false negative and false positive detection in MMAD is less straightforward to conduct than in PAMGUARD, as the software does not log individual detections and does not indicate detections in spectrograms by colouring detected elements.
In general, the many false negative and false positive detections show that it is difficult to find generally applicable detection parameters to achieve low numbers of both. Thus, trained staff will be needed to supervise at least the initial phase of using detection programs for monitoring marine mammal presence and abundance. For PAMGUARD, it is recommendable that trained staff initially adjusts and optimises detection parameters and possibly add more detectors to optimise detection
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of specific marine mammal vocalisations, such as relatively short or less harmonic humpback moans. For MMAD, it is recommendable that set detection parameters are adjusted by KAON using recordings of the specific sites the program will be used. For both programs, it is important to verify detections by checking the spectrograms before taking action or analysing data.
In general, MMAD comes with an easier to use interface, however, it leaves less flexibility to adjust detection parameters or add specific detectors for specific user needs, as well as it is not possible to assess detection precision as detailed as in PAMGUARD. However, as PAMGUARD is an open source software and no full-time support staff is available, support may not be provided to a level and extent KAON is able to offer. Developers of MMAD are highly flexible and approachable, and the software can be modified to specific user needs. Thus, it will depend on the end user’s needs, budget and expertise whether PAMGUARD or MMAD will be the preferable choice. For applications with Ultra Electronics sonobuoys, a practicable solution may be to offer sonobuoys with the option to integrate MMAD for end users not extensively trained on the use of marine mammal detection programs. Another solution would involve investing more work in the development of an easier to use user interface with detection algorithms and a module-like structure based on PAMGUARD, thus allowing a higher level of user control over parameter settings and algorithms to integrate.
NERC MRE knowledge exchange internship as a tool to use knowledge acquired by academic research for commercial interests
This internship gave me the unique opportunity to get an insight into a section of a commercial organisation specialised in active and passive sonar. It also allowed me to view my research area of effects of anthropogenic noise on aquatic organisms from a different angle and taught me the different stages involved in developing and modifying a device for wider commercial use. The internship also integrated me into the BARC consortium, a group of researchers and physicists of commercial and academic background monitoring anthropogenic noise emission and investigating its effect on marine ecosystems in a more holistic and integrative approach at an area, in which construction and operation of an offshore windfarm is planned for 2014/2015.
The internship revealed that the majority of PAM users, as well as regulators and engineers, still focus on anthropogenic impacts on marine mammals, ignoring effects on other animals, such as fish and invertebrates, even though marine mammals heavily depend on them as their main food source. Clearly, more work is needed to increase awareness and knowledge about impacts of anthropogenic
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noise on other aquatic organisms than marine mammals. This will also be necessary in order to move technical developments forward to integrate particle motion quantifications and other measurements relevant to other organisms and to increase research projects with a more holistic approach.
This internship showed that combining commercial work with research work can be difficult, as careers in academia differ from careers in industry. For instance, proceeding in a research career requires publication of original work in peer-reviewed journals driving the research field forward so that research funding can be secured for specific projects of fixed time-scales of a few months to a few years. Thus, researchers are moving from project to project, while business partners of some companies tend to be employed with fixed contracts, determining the role of the employee within the company rather than goals to be achieved by a specific project. Thus, work focus and timescales can differ substantially between research and business partners potentially leading to conflicts of interests.
Future projects will need to take this aspect into account when linking researchers with business partners, to favour projects enabling researchers to feed their research results into applications of everyday life (for example by using a device under development to generate new data), rather than evaluating potentials of products for wider commercial use. This is especially important in more applied research fields, such as conservation, in which researchers are already facing conflicts of interest between the requirement of high quality research to deliver ground breaking findings and applied research requiring systematic data on different aspects of an already known effect to map species differences, the role of specific environmental contexts, and related topics to increase specific knowledge needed for effective regulation of human activities.
Acknowledgements
I thank especially my internship supervisor Peter Dobbins for giving me the opportunity for this project and his supervision, Steve Goodwin and the management of Ultra electronics for having me, Lynne and Federica for providing marine mammal acoustic recordings, Michael Ainslie, Paul Lepper, Dick Hazelwood, Nathan Merchant, and Joanne Garrett for acoustic discussions. I also thank Per Berggren, Simon Laing, Silvana Neves, Danielle Harris and Doug Gillespie for discussions on marine mammal detection, and Marc Armstrong for letting us have an adapted copy of the MMAD computer program for evaluation.
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References
Ainslie, M. A. 2011. Standard for measurement and monitoring of underwater noise, Part I: physical quantities and their units. TNO Report TNO-DV 2011 C235, 2011. Au, W. W. L. 1993. The sonar of dolphins. New York, Berlin, Heidelberg: Springer. Au, W. W. L. & Hastings, M. C. 2008. Principles of marine bioacoustics. p. 679. New York: Springer. Barber, J. R., Crooks, K. R. & Fristrup, K. M. 2010. The costs of chronic noise exposure for terrestrial organisms. Trends in Ecology & Evolution, 25, 180-189. Blumstein, D. T., Mennill, D. J., Clemins, P., Girod, L., Yao, K., Patricelli, G., Deppe, J. L., Krakauer, A. H., Clark, C., Cortopassi, K. A., Hanser, S. F., McCowan, B., Ali, A. M. & Kirschel, A. N. G. 2011. Acoustic monitoring in terrestrial environments using microphone arrays: applications, technological considerations and prospectus. Journal of Applied Ecology, 48, 758-767. De Jong, C. A. F., Ainslie, M. A. & Blacquière, G. 2011. Standard for measurement and monitoring of underwater noise, Part II: procedures for measuring underwater noise in connection with offshore wind farm licensing. TNO Report TNO-DV 2011 C251. Discovery of Sound in the Sea (DOSITS). 2013. Low Frequency Analysis And Recording (LOFAR) sonobuoy. Available at: http://www.dosits.org/technology/locatingobjectsbylisteningtotheirsounds/lowfrequencyanalysisan dranginglofarsonobuoy/. Last accessed: 25 September 2013. Doherty, P. J. 1987. Light-traps: selective but useful devices for quantifying the distributions and abundances of larval fishes. Bulletin of Marine Science, 41, 423-431. Gillespie, D., Mellinger, D., Gordon, J., McLaren, D., Redmond, P., McHugh, R., Trinder, P., Deng, X. & Thode, A. 2009. PAMGUARD: Semiautomated, open source software for real-time acoustic detection and localization of cetaceans. Journal of the Acoustical Society of America, 125, 2547–2547 Goodall, C., Chapman, C. & Neil, D. 1990. The acoustic response threshold of the Norway lobster, Nephrops norvegicus (L.) in a free sound field. In: Frontiers in crustacean neurobiology (Ed. by K. Wiese, W. D. Krenz, J. Tautz, H. Reichert & B. Mulloney), pp. 106-113. Basel: Birkhäuser. Longcore, T. & Rich, C. 2004. Ecological light pollution. Frontiers in Ecology and the Environment, 2, 191-198. Lucke, K., Winter, E. & Lam, F.-P. In Prep. White-paper on underwater noise regulations. Workshop on international harmonisation of approaches to define underwater noise exposure criteria / Budapest, 17th August 2013. Mellinger, D. K. 2001. Ishmael 1.0 User's Guide. Seattle. Northridge, S. P., Tasker, M. L., Webb, A. & Williams, J. M. 1995. Distribution and relative abundance of harbour porpoises (Phocoena phocoena L.), white-beaked dolphins (Lagenorhynchus
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albirostris Gray), and minke whales (Balaenoptera acutorostrata Lacepède) around the British Isles. ICES Journal of Marine Science: Journal du Conseil, 52, 55-66. Nowacek, D. P., Thorne, L. H., Johnston, D. W. & Tyack, P. L. 2007. Responses of cetaceans to anthropogenic noise. Mammal Review, 37, 81-115. Payne, R. S. & McVay, S. 1971. Songs of Humpback Whales. Science, 173, 585-597. Popper, A. N. & Fay, R. R. 2011. Rethinking sound detection by fishes. Hearing Research, 273, 25-36. Popper, A. N. & Hastings, M. C. 2009. The effects of anthropogenic sources of sound on fishes. Journal of Fish Biology, 75, 455-489. Salmon, M. 1971. Signal characteristics and acoustic detection by the fiddler crabs, Uca rapax and Uca pugilator. Physiological Zoology, 44, 210–224. Shirihai, H. 2006. Whales, dolphins and seals: a field guide to the marine mammals of the world. London: A & C Black Publishers Ltd. Silber, G. K. & Bettridge, S. 2006. United States’ actions to reduce the threat of ship collisions with north Atlantic right whales. Paper IWC/58/CC8 presented at the IWC Scientific Committee, St. Kitts. Williams Hodge, L. E. 2011. Monitoring marine mammals in Onslow Bay, North Carolina, using passive acoustics. PhD thesis, Duke University. Zimmer, W. M. X. 2011. Passive acoustic monitoring of cetaceans. Cambridge: Cambridge University Press.
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Appendix 1: Sonobuoy description
Original description of Ultra Electronics SSQ 906G LOFAR sonobuoys:
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Appendix 2: SurveyMonkey questionnaire
Questionnaire published in SurveyMonkey
PAGE 1
Background Information
Thank you for joining in.
This survey is being conducted as part of an ongoing study to investigate the state of the art in PAM systems and to find out where users consider the gaps in the available capability lie and where further research and development should be aimed to meet their requirements.
In particular we would like to explore the ways in which military sonobuoys might be modified to make them more useable for marine mammal monitoring and ambient noise measurement.
If you are a user of PAM equipment, we should be extremely grateful if you would complete this survey. It shouldn’t take more than a few minutes and the information will be used for statistical purposes only. Your name and contact details will not be associated with the results and will certainly not be passed on to any third parties.
The survey begins here:
Question 1
1. Are you/your organisation
An academic institution?
A government research organisation?
A commercial research organisation?
An oil and gas exploration and production organisation?
A PAM service provider to the oil and gas industry?
A renewable energy organisation?
A PAM service provider to the renewable energy sector?
A regulatory organisation?
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A branch of the military?
An outreach or leisure organisation?
Other (please specify)
Question 2
2. How many PAM systems do you currently operate?
1
2-5
6-10
More than 10
Please give a brief description of these systems
Question 3
3. What, approximately, is the total use of these systems in a period of one year?
Less than a week?
A week to a month?
One to three months?
Three to six months?
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Six to nine months?
Nine months to a year?
More than a year?
PAGE 2
Your Application
With questions 4 and 5 we would like to learn precisely what sounds you want to monitor to assess your requirements for parameters such as bandwidth, sampling rate, and dynamic range.
Question 4
4. Are you interested in (choose all that apply)
Marine mammal vocalisations and clicks?
Non-marine mammal sound production?
Seismic noise?
Other natural abiotic noise?
Anthropogenic noise?
Acoustic environment characterisation?
Sound propagation model evaluation?
Other (please specify)
Question 5
5. If you are monitoring marine mammals, please tick the species of most interest (all that apply)
Porpoises
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Oceanic Dolphins
River Dolphins
Orcas
Sperm Whales
Beaked Whales
Belugas and Narwhals
Right and Bowhead Whales
Rorquals
Gray Whales
Harbour Seals
Grey Seals
California Sea Lions
Steller Sea Lions
Other (please specify)
PAGE 3
Proposed Specification
In questions 6 and 7, we list potential specifications for our proposed PAM buoy and the software package that accompanies it. We would like to know how essential these features will be for your purposes, along with suggestions for other features. All comments and suggestions will be gratefully received.
Question 6
6. Here are potential outline specifications for the hardware in a new sonobuoy PAM system. Please select "yes" if the respective feature will be essential to you, "no", if it is irrelevant to you,
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and "not essential", if it will be helpful for additional or future data collection, but not essential for your project at the moment.
yes no not essential
Small, lightweight, hand deployed by one person from small boat
Recoverable, reusable buoy with rechargeable battery
GPS/compass positioning
Data logger recording temperature, salinity, pH
Directional hydrophones
Hydrophone depth selectable 15/30/60 m
Maximum depth more than 60 m
Maximum depth more than 300 m
Drogue and compliant hydrophone suspension to minimise flow noise and surface motion interference
HiFi quality signal 10Hz – 20kHz
Compressed signal 10kHz – 150kHz
FM radio telemetry – line of sight range 5km or more for boat mounted receiver
Up to 100 selectable independent transmission channels
On-board full bandwidth backup recording
Please comment on these suggestions or list any other hardware features you would consider important
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Question 7
7. Here are potential outline specifications for the receiver/software in a new sonobuoy PAM system. Please select "yes" if the respective feature will be essential to you, "no", if it is irrelevant to you, and "not essential", if it will be helpful for additional or future data collection, but not essential for your project at the moment.
yes no not essential
Choice of single or multi-channel (up to 8) FM receiver
Receiver output transferred directly to computer and recorded on hard disk
Dedicated software package displays signal waveforms and spectra for all channels or waveform, spectrum and spectrogram for single selected channel
In-built detection algorithms of marine mammal vocalisations
In-built species identification algorithms based on clicks, whistles and other vocalisations in addition to detection
Bearing localisation with single buoy
Localisation in range and bearing with three or more buoys and range, bearing and depth with four or more buoys
Plan and waterfall displays for detections
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Programmable alerts for presence of selected species or any cetacean within selected range
Amendable settings during recording sessions/interactive device control
Adjustable recording levels
Please comment on these suggestions or list any other features you would consider important
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Conclusion
Finally, we would like to hear any comments you have on passive acoustic monitoring in general and the equipment currently available. Could you comment in particular on whether there are specific features missing in the system you are currently using you would like to incorporate in your future projects?
Question 8
8. Your comments please
Thank you, that is the end of the survey. If you are happy with your answers, please click the “done” button to submit them.
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Appendix 3: Marine mammal detector settings
PAMGUARD settings:
Spectrogram engine settings underlying detection parameters:
Spectrogram settings Click removal filter settings
Spectral noise filter settings
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Settings for moan detector:
Detection parameter settings Filter and detection threshold settings
Settings for whistle detector
Detection parameter settings Filter and detection threshold settings
Click detector settings:
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Click high pass filter settings:
Click detection parameter settings (left to default settings):
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Spectrogram view
Click detector view:
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Settings for KAON MMAD
Settings were left at default: odontoceteWhistleSensitivity = 1.0 odontoceteClickSensitivity = 1.0 spermClickSensitivity = 1.0 hfMysticeteWhistleSensitivity = 1.0 lfMysticeteWhistleSensitivity = 1.0
alarmThreshold = 70.0 warningThreshold = 50.0 odontoceteDisplayDecimation = 4 hfMysticeteDisplayDecimation = 2 lfMysticeteDisplayDecimation = 1
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