Tetsuo Fukuchi

Approaching whales by autonomous Underwater vehicle

There are few studies on the ecology of whales in underwater except for small whales (Baird, R., 1996, Otani, S., 1998). It is hoped that through the use of Autonomous Underwater Vehicles (AUVs) new knowledge about whales can be gained. The whale makes sounds, and especially the humpback whale (Megaptera novaeangliae) makes a specific sound called a song. We started our project to develop the technology for AUVs to follow and observe humpback whales by analyzing their songs and locating them underwater. A small size passive SONAR was designed, fabricated, and fitted on the AUV AQUA EXPLORER 2000. An observation experiment was conducted in March 2001 off the Kerama Islands, Okinawa. Prior to our studies, there were no examples of AUV observations on whales anywhere in the world. This experimental observation was conducted as a joint project of the Underwater Technology Research Center at the Institute of Industrial Science in the University of Tokyo, KDDI Co. Research Institute, and the Okinawa EXPO Aquarium. The AUV succeeded in detecting a humpback whale underwater and approaching it within 50m in this experiment.

Beam pattern estimation of clicks of a free-ranging Ganges river dolphin

The first recordings of bio-sonar clicks of free-ranging Ganges river dolphin (Platanista gangetica) were made in Budhabalanga river in Orissa, India. The system used for recording is a 3.2 meter long array composed of three hydrophones forming an equispaced linear SBL array and another two hydrophones in conjunction with the central hydrophone forming a small SSBL triangular array in a plane perpendicular to the array axis. The array structure was deployed both in horizontal and vertical configurations. The clicks of the dolphin received on each hydrophone were sampled at a rate of 500 kHz per channel. From the sampled clicks data, the sonar transmit beam pattern of the dolphin in both horizontal and vertical plane was estimated using difference of ASL (apparent source level of the click signal) and the absolute angles of the dolphins location between the central hydrophone and the other two peripheral hydrophones for the on-axis clicks. To estimate more accurate beam pattern, conditions for selection of on-axis clicks were well-considered, and thus we propose a new criteria for determining on-axis clicks. In this method, we assume that the dolphins beam pointing direction is towards the central hydrophone and its beam pattern is symmetrical. However, actual measurement of ASL from three hydrophones shows that values at the peripheral hydrophones are not always same. This suggests that the dolphins beam is not pointing exactly towards the central hydrophone so that the central hydrophones ASL is not the real peak value of the beam. We propose a refinement in the beam pattern estimation method using interpolation and curve fitting to obtain an improved estimate of the Ganges river dolphins beam pattern. By analyzing all available clicks, we have estimated the dolphins beam pattern in both horizontal and vertical plane. The 3-dB beamwidth is found to be approximately 10 degrees in horizontal plane and 14 degrees in vertical plane. In this paper, we propose the new beam pattern estimation method using interpolation and curve fitting.

Techniques for segregation and classification of several vocalizing sperm whales for AUV-based localization applications

Sperm whales are amongst the most vocally active cetaceans. A fuller knowledge of these whales and their clicking behavior can be obtained by creating a picture of the relative locations of sperm whales in a region of interest and also by tracking them individually in three dimensions. This paper reports a major step in this direction by the development of automatic techniques for segregation of several clicking individuals and to generate a de-interleaved time series of their individual vocalizations. We discuss methods to extract the clicks from hydrophone data and for individual classification based on various click parameters: time-delay between (hydrophones, inter-pulse-interval within a click, correlation with a reference, and the peak frequency. We present results of our techniques for automatic segregation and classification of several sperm whales using data collected from a 2-hydrophone array. These results demonstrate their suitability for a compact real-time implementation on AUVs.

Estimates of bio‐sonar characteristics of a free‐ranging Ganges river dolphin

This paper reports the first known studies of the bio‐sonar characteristics of an isolated free‐ranging Ganges river dolphin, Platanista gangetica. The animal preferred to roam in a deeper tract of the otherwise shallow river. The click sounds of the dolphin were recorded over a period of 2 days on a 3.2‐meter‐long high‐frequency hydrophone array composed of three hydrophones forming an equispaced linear array and another two hydrophones in conjunction with the central hydrophone forming an SSBL triangular array in a plane perpendicular to the array axis. The array was deployed both in horizontal and vertical configurations. The array structure provided 3‐D measurements of the source location through measurement of the interelement time delay. Bio‐sonar characteristics such as click duration, bandwidth, and interclick intervals in click trains have been reported. Measurements of dolphin track and the relative click levels on the array hydrophones have been used to obtain a preliminary characterization of ...

Passive tracking of multiple diving sperm whales using single hydrophones at two mobile locations

A simple method using only two hydrophones, each loosely deployed from separate mobile platforms, has been developed to simultaneously track several vocalizing sperm whales. The separation distance of several hundred meters between the hydrophones implies that a particular whale could present vastly different beam orientations towards them, thus precluding use of any specific relationship between the click signal levels at the two locations for the purpose of whale localization. This method utilizes time‐of‐arrival of the direct clicks and their surface reflections and matches them at the two hydrophone locations. Whales are segregated on the basis of the set of observed time delays. Click parameters such as interpulse interval and average click frequency are proposed to be used as secondary data for the purpose of track refinement. Depth profile of the whales is obtained independent of the separation distance between the two hydrophones. However, knowledge of the separation distance between the hydrophon...

A Passive Sonar System for Searching Acoustic Beacons in Deep Sea

Authors developed a passive sonar system for searching rocket boosters with acoustic beacons, which will be launched by JAXA with H2A rocket, detached from the rocket, and sink under deep sea. The system consists of an underwater unit that can be operated at 6500 m deep and an onboard unit with signal processing and display functions. The underwater unit is mounted on ROV which is towed by a mother ship at 500~1000 m above the bottom. The system provides detection and a localization functions. The detection is realized by using two linear, multi-element, hydrophone arrays receiving acoustic pulses radiated from acoustic beacons from both sides, multi- beam formers, and waterfall displays. The localization is realized by using a 4-element planar hydrophone array and an SSBL acoustic positioning signal processing. The acoustic signals received by the hydrophone arrays are digitized and transmitted to the onboard unit via an optical fiber cable. The onboard unit consists of two PCs, which execute signal processing and display functions.