Chew Jee Loong
Email Address
tmscjl@nus.edu.sg
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Publication Is synthetic aperture an essential tool for echoic shape recognition in dolphins?(2011) Hoffmann-Kuhnt, M.; Chitre, M.; Wellard, R.; Lee, J.; Abel, G.; Yeo, K.; Chew, J.-L.; ELECTRICAL & COMPUTER ENGINEERING; TROPICAL MARINE SCIENCE INSTITUTEA dolphin had previously been trained to perform a cross-modal matching-to-sample task. In one version of this task the animal had to investigate a sample object that was concealed in a box through its echolocation sense alone, then select the correct match among up to three alternative objects visually in air. Given the frequency range of a dolphin click and the limited number of sensors that the dolphin receives the sonar returns with, the dolphin should have difficulties resolving the details of the object. We suggested earlier that the dolphin might be using synthetic aperture to gain a higher resolution of the stimulus. To test this hypothesis we proposed to restrict the movement of the dolphin by stationing him on a bite-plate that was fixed in front of the box that contained the sample object. We trained the dolphin to station on the bite-plate while performing the cross-modal task (echolocation to vision) while recording the sound field around the dolphin through a 16-hydrophone array that was placed in a variety of positions and configurations between the object and the dolphin stationed on the bite-plate. The acoustic data were recorded at 500 kHz and later analyzed. To our surprise the dolphin was still able to perform the discrimination task. In this paper, we present the analysis of the data collected and show that the dolphin employs techniques such as beam steering and beam shaping while acoustically interrogating the object. This suggests that while the dolphin might still employ a synthetic aperture when possible, he might not need it to resolve the details of the object. We are planning to extend the range of objects to new and unfamiliar objects to explore whether the dolphin is indeed able to resolve details of the object acoustically without the need for synthetic aperture. © 2011 MTS.Publication STARFISH - A small team of autonomous robotic fish(2011-04) Koay, T.B.; Tan, Y.T.; Eng, Y.H.; Gao, R.; Chitre, M.; Chew, J.L.; Chandhavarkar, N.; Khan, R.R.; Taher, T.; Koh, J.; ELECTRICAL & COMPUTER ENGINEERING; TROPICAL MARINE SCIENCE INSTITUTESTARFISH AUVs (Autonomous Underwater Vehicles) are a group of open architecture vehicles with high degree of modularity and well defined mechanical, electrical, and software interfaces. This enables the baseline AUV configuration to be simple and low in cost, while allowing its capabilities to be extended with various specialized modules depending on the need. Various AUVs can easily be configured in different ways to form a team of heterogeneous AUVs tailored to a specific mission. STARFISH AUVs employ a flexible Command and Control (C2) architecture that is capable of adapting to various configurations of AUVs. The vehicle command is loosely based on the C2 hierarchy in submarines, with software agents such as Captain, Executive Officer, Navigator, etc interacting to each other to control the AUV's behaviors. Numerous field trials have been conducted in open waters. Results from some of these trials are presented in this paper to illustrate the capability of deploying a heterogeneous team of cooperative AUVs. Specifically, the mission illustrated shows how a single AUV with high positioning accuracy can be used to reduce the positioning error of one or more AUVs with poorer navigational sensors.