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Author

Ryo Hirotsu

Bio: Ryo Hirotsu is an academic researcher from Waseda University. The author has contributed to research in topics: Sperm whale & Whale. The author has an hindex of 2, co-authored 4 publications receiving 32 citations.
Topics: Sperm whale, Whale, White noise, Noise, Population

Papers
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Journal ArticleDOI
TL;DR: The proposed sperm whale click analysis scheme is able to localize the positions of the whales in a group using data received at two arrays deployed near the surface using the three-dimensional underwater trajectories of six sperm whales.
Abstract: In this paper, a sperm whale click analysis scheme is proposed in order to calculate the position of individual sperm whales in a group using data received at two arrays deployed near the surface. The proposed method mainly consists of two parts: short baseline (SBL) with classification and long baseline (LBL) with class matching. In SBL with classification, a click is automatically detected, and its direction of arrival is calculated. The clicks are then classified based on their direction vectors. The class data are then sent together with direction data and matched to the other array’s class data. LBL with class matching is used for localization. The classification algorithm can be used to estimate the number of whales clicking and to list potential candidates for LBL matching. As a result, the proposed method is able to localize the positions of the whales in a group. The performance of the proposed method is evaluated using data recorded off Ogasawara islands with two arrays near the surface. The three-dimensional underwater trajectories of six sperm whales are extracted to demonstrate the capability of the proposed method.

22 citations

Proceedings ArticleDOI
01 May 2006
TL;DR: In this paper, an AUV was used as an observation platform of sperm whales in order to estimate the position of a specific sperm whale by listening to their clicks and detecting its direction.
Abstract: Sperm whales are known to dive to a depth of over two thousand meters and it is also known that they emit loud impulsive broadband sounds called "clicks" during their diving. But little is known about sperm whales' behavior because they dive more than one thousand meters. So authors propose to use the autonomous underwater vehicle (AUV) as an observation platform of sperm whales. Our final goal is to develop and construct the system so that AUV can estimate the position of sperm whales by a passive technique listening to their clicks, and can track a specific sperm whale. The tasks of the AUV are to recognize sperm whales individually and track them in real time by listening to sperm whale's clicks with 4-hydrophone array and detecting its direction. In September 2005, we carried out an experiment to test this AUV-based observation system off Ogasawara Islands using AUV AE2000 in the depth of 1000 meters. During the experiments over eight days, we had ten dives and succeeded in recording of the click sound by both the AUV and the mother vessel. But it was difficult to calculate the direction of a whale in real-time on the AUV because the sound level of clicks was low and the sound noise generated by AUV itself was high. According to the off-line analysis, we found out that clicks can be detected by the AUV while all actuators on the AUV were stopped.

9 citations

Proceedings ArticleDOI
01 Dec 2008
TL;DR: In this article, a passive acoustic system consisting of an AUV (Autonomou Underwater Vehicle) with a hydrophone array and two arrays attached to a support ship was used to observe the underwater behavior of sperm whales.
Abstract: In order to observe the underwater behavior of sperm whales, the authors previously introduced a passive acoustic system that consists of an AUV (Autonomou Underwater Vehicle) with a hydrophone array and two arrays attached to a support ship. The three arrays receive sperm whale clilicks and determine the direction to the sound source by a SBL (Short Baseline) system. Based on triangulation with a pair of arrays, it is possible to calculate the location of the sound source in real-time. Sperm whales usually dive in groups, and so each array captures thousands of clicks from multiple whales. It is, therefore, necessary to identify the corresponding clicks of each individual captured by the three arrays. However, the acoustic communication band between the AUV and the support ship is limited, so it is impossible to correlate the clicks received by each array in real-time. In order to triangulate with a limited communication band, the authors introduce a click classification scheme at each array considering the individual sound source. The class data is sent together with direction data to the AUV and an array on the support ship. Thus the AUV and the operator in the support ship can estimate the positon of the whale by a LBL (Long Baseline) system. In this paper, the proposed classification algorithm is applied to data recorded off Ogasawara in 2003. The clicks can be classified reasonably by the proposed method. The three-dimensional underwater trajectories of six sperm whales are obtained by using the classes obtained by the proposed method.

2 citations

Proceedings ArticleDOI
01 Jan 2006
TL;DR: The result shows that proposed method can extract IPI in good conformity with those by convention method under the condition of low lever noise.
Abstract: Inter-pulse interval (IPI) of the click projected from a sperm whale (phyeter macrocephalse) is expected to represent its size. IPI can be regarded as a distinguishing feature between individual sperm whales. Correlation analysis is used to measure IPI from recorded data. We analyzed data recorded off Ogasawara from 2003 to 2005 based on the correlation analysis. Although the results show its applicability for identification of individuals in data of 2003, it does not provide reasonable results for data recorded in 2004 and 2005, which include more noise comparing to those of 2003 when the noise in support vessel is not negligible. In this paper, we propose a new analysis method of sperm whale click based on MUSIC (multiple signal classification) algorithm in order to calculate IPI. MUSIC algorithm is the high-resolution frequency estimation method using orthogonality of signal and noise subspaces. It is said that it has high capacity for white noise. By estimating IPI from clicks data by proposed method and comparing to them to those by convention method, we examine applicability of MUSIC algorithm to classify individuals of sperm whale of analysis of data recorded in 2003. The result shows that proposed method can extract IPI in good conformity with those by convention method under the condition of low lever noise.

1 citations


Cited by
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Journal ArticleDOI
TL;DR: A four-hydrophone small-aperture array was coupled to an autonomous acoustic recorder and used for long-term tracking of high-frequency odontocete sounds, providing swimming and diving behavioral information for free-ranging animals using a single instrument.
Abstract: To track highly directional echolocation clicks from odontocetes, passive hydrophone arrays with small apertures can be used to receive the same high frequency click on each sensor. A four-hydrophone small-aperture array was coupled to an autonomous acoustic recorder and used for long-term tracking of high-frequency odontocete sounds. The instrument was deployed in the spring of 2009 offshore of southern California in a known beaked whale and dolphin habitat at about 1000 m depth. The array was configured as a tetrahedron with approximately 0.5 m sensor spacing. Time difference of arrival measurements between the six sensor-pairs were used to estimate three-dimensional bearings to sources. Both near-seafloor beaked whales and near-sea surface dolphins were tracked. The tracks observed using this technique provide swimming and diving behavioral information for free-ranging animals using a single instrument. Furthermore, animal detection ranges were derived, allowing for estimation of detection probability functions.

42 citations

Journal ArticleDOI
TL;DR: In this paper, the authors presented the design and proof of concept of a streamlined, low-cost, and smooth-hulled underwater vehicle, miniature animal safe underwater vehicle (MASUV-1), utilizing an entirely enclosed propulsion and steering system.
Abstract: In this paper, we present the design and proof of concept of a streamlined, low-cost, and smooth-hulled underwater vehicle, miniature animal safe underwater vehicle (MASUV-1), utilizing an entirely enclosed propulsion and steering system. This allows for safely operating MASUV-1 in the vicinity of marine mammals, and thus, facilitates animal behavior research as well as coping with traditional engineering and scientific missions in marine mammal populated environments. The vehicle utilizes an ad hoc designed multidirectional thrust-vectoring system for steering, based on multiple servo motors and pushrods. Tests of the vehicle in a stillwater environment show high maneuverability at speeds comparable with similar torpedo-type class underwater vehicles.

41 citations

Journal ArticleDOI
TL;DR: In this paper, a literature review of marine mammal sounds made by marine mammals in Australian waters is presented, which includes recordings from Australia of Omura's whales (Balaenoptera omurai), dwarf sperm whales (Kogia sima), common dolphins (Delphinus delphis), short-finned pilot whales (Globicephala macrorhynchus), long- finned pilot whale (G. melas), Fraser’s dolphins (Lagenodelphis hosei), false killer whales (Pseudorca crass
Abstract: The study of marine soundscapes is a growing field of research. Recording hardware is becoming more accessible; there are a number of off-the-shelf autonomous recorders that can be deployed for months at a time; software analysis tools exist as shareware; raw or preprocessed recordings are freely and publicly available. However, what is missing are catalogues of commonly recorded sounds. Sounds related to geophysical events (e.g. earthquakes) and weather (e.g. wind and precipitation), to human activities (e.g. ships) and to marine animals (e.g. crustaceans, fish and marine mammals) commonly occur. Marine mammals are distributed throughout Australia’s oceans and significantly contribute to the underwater soundscape. However, due to a lack of concurrent visual and passive acoustic observations, it is often not known which species produces which sounds. To aid in the analysis of Australian and Antarctic marine soundscape recordings, a literature review of the sounds made by marine mammals was undertaken. Frequency, duration and source level measurements are summarised and tabulated. In addition to the literature review, new marine mammal data are presented and include recordings from Australia of Omura’s whales (Balaenoptera omurai), dwarf sperm whales (Kogia sima), common dolphins (Delphinus delphis), short-finned pilot whales (Globicephala macrorhynchus), long-finned pilot whales (G. melas), Fraser’s dolphins (Lagenodelphis hosei), false killer whales (Pseudorca crassidens), striped dolphins (Stenella coeruleoalba) and spinner dolphins (S. longirostris), as well as the whistles and burst-pulse sounds of Australian pygmy killer whales (Feresa attenuata). To date, this is the most comprehensive acoustic summary for marine mammal species in Australian waters.

41 citations

Journal ArticleDOI
TL;DR: In this paper, the authors identify and describe operationally-feasible methods to alter adjust the way in which industry ROVs are operated to enhance the scientific value of data that they collect, without significantly impacting scheduling or adding to deployment costs.
Abstract: Remotely-operated vehicles (ROVs) are used extensively by the offshore oil and gas and renewables industries for inspection, maintenance, and repair of their infrastructure. With thousands of subsea structures monitored across the world’s oceans from the shallows to depths greater than 1000 m, there is a great and underutilised opportunity for their scientific use. Through slight modifications of ROV operations, and by augmenting industry workclass ROVs with a range of scientific equipment, industry can fuel scientific discoveries, contribute to an understanding of the impact of artificial structures in our oceans, and collect biotic and abiotic data to support our understanding of how oceans and marine life are changing. Here, we identify and describe operationally-feasible methods to alter adjust the way in which industry ROVs are operated to enhance the scientific value of data that they collect, without significantly impacting scheduling or adding to deployment costs. These include: rapid marine life survey protocols, imaging improvements, the addition of a range of scientific sensors, and collection of biological samples. By partnering with qualified and experienced research scientists, industry can improve the quality of their ROV-derived data, allowing the data to be analysed robustly. Small changes by industry now could provide substantial benefits to scientific research in the long-term and improve the quality of scientific data in existence once the structures require decommissioning. Such changes also have the potential to enhance industry’s environmental stewardship by improving their environmental management and facilitating more informed engagement with a range of external stakeholders, including regulators and the public.

39 citations

Journal ArticleDOI
TL;DR: Localization and tracking of dolphins over long periods has the potential to provide insight into their ecology, behavior, and potential response to stimuli.
Abstract: Dolphins are known to produce nearly omnidirectional whistles that can propagate several kilometers, allowing these sounds to be localized and tracked using acoustic arrays. During the fall of 2007, a km-scale array of four autonomous acoustic recorders was deployed offshore of southern California in a known dolphin habitat at ∼800 m depth. Concurrently with the one-month recording, a fixed-point marine mammal visual survey was conducted from a moored research platform in the center of the array, providing daytime species and behavior visual confirmation. The recordings showed three main types of dolphin acoustic activity during distinct times: primarily whistling during daytime, whistling and clicking during early night, and primarily clicking during late night. Tracks from periods of daytime whistling typically were tightly grouped and traveled at a moderate rate. In one example with visual observations, traveling common dolphins (Delphinus sp.) were tracked for about 10 km with an average speed of ∼2.5 m s−1 (9 km h−1). Early night recordings had whistle localizations with wider spatial distribution and slower travel speed than daytime recordings, presumably associated with foraging behavior. Localization and tracking of dolphins over long periods has the potential to provide insight into their ecology, behavior, and potential response to stimuli.

28 citations