NDLI: Signal processing applied to the dolphin-based sonar system

Content Provider	IEEE Xplore Digital Library
Author	Houser, D. Martin, S. Phillips, M. Bauer, E. Herrin, T. Moore, P.
Copyright Year	2003
Description	Author affiliation: BIOMIMETICA, La Mesa, CA, USA (Houser, D.)
Abstract	The bottlenose dolphin has evolved a unique system of biosonar, or echolocation, that allows it to exploit a visually limited littoral niche. The effectiveness of dolphin echolocation at finding and identifying submerged objects is unsurpassed by man-made hardware systems built for similar tasks. It has become a model system from which to draw hardware and signal processing design concepts and is the basis for the development of biomimetic mine-hunting systems of the shallow water (SW) and very shallow water (VSW) zones. The Dolphin Based Sonar (DBS) system is a proof-of-concept sonar system designed for operations in the SW/VSW environments that incorporates characteristics of dolphin sonar transmission and structural elements of dolphin auditory anatomy. Specifically, the system is designed to reproduce dolphin signal types and source levels and to match the animal's transmission and reception beam patterns, directivity indices, receive sensitivity, and auditory filtering capabilities. The DBS, built as part of a cooperative agreement with SPAWARSYSCEN - San Diego (SSC-SD) and Applied Research Laboratories, University of Texas (ARL-UT), consists of a topside unit (dry-end computer) and wet-end unit (sonar head and connections). The wet-end unit, constructed by ARL-UT, is integrated around the Analog Devices SP 21061 SHARC processor architecture. Both the projector and receiver array were made from 1-3 piezocomposite transducer material. The projector has a 12 degree beam width at 110 kHz with sidelobes on the order of /spl sim/17 dB. It is capable of delivering echolocation click-like synthetic waveforms and FM chirps and sweeps with source levels up to 206 dB re: 1 /spl mu/Pa@120 kHz. Signals can be transmitted at a frequency range of 30 to 120 kHz and with an 80 kHz 10-dB bandwidth. Correlation coefficients between "real" and "synthetic" wideband and low-frequency unimodal echolocation clicks were 0.95 on the maximum response axis (MRA). The receiver employs two directional hydrophones with beam widths of 20-degrees at 80 kHz. The matched receivers are separated /spl sim/12.5 cm, the approximate distance between the ears of the bottlenose dolphin. The projector and receivers are attached to a pan-and-tilt unit that permits +/- 170 degrees of pan and +/- 170 degrees of tilt. The DBS has been tested on the placement of known targets across a bay silt and mud bottom (categorized as a B2 type bottom) as well as on the detection of a human diver in the water column. Testing was done from a fixed-position on a stationary piling and from a variable-position, the latter providing multi-aspect data via movement along a 100 m trolley system (long-line). Fixed piling testing included the placement of 4 proud mine-shapes and 3 non-mine bottom objects (NOMBOS). Long-line testing included the placement of 8 proud mine-shapes, 4 PVC markers, and naturally accumulated man-made clutter. A matched filter detector was used for initial detection of targets in acoustic returns and has been combined with a spectral detector to reduce the false alarm rate. Cross-correlation beam forming (CCBF) and the Chirp Corporation's adaptive beam former (ABF) were evaluated to assess beam-forming processing of the two receivers. A "snippet" algorithm was developed for isolation of regions of interest existing within a Cartesian coordinate map created from successive sonar returns. Visualization of the map was increased to a 5 cm resolution and further refined via additional energy thresholding by application of a Cartesian binary mask. The mask was created by replacing Cartesian cell values with a 1 or 0, depending upon a minimum number of returns per total number of scans, and multiplying the binary mask by the original Cartesian map. Approximately 40 target features have been identified for potential use in target classification. Classification testing is currently limited to using 8-10 of the most useful features identified to date. Results to date
Sponsorship	Dept. of the Navy Sci. and Technol. Coalition for Enhanced Marine Resources Orincon Ceros Harbour Offshore Inc
Starting Page	297
Ending Page	303
File Size	541278
Page Count	7
File Format	PDF
ISBN	0933957300
DOI	10.1109/OCEANS.2003.178572
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2003-09-22
Publisher Place	USA
Access Restriction	Subscribed
Rights Holder	MTS
Subject Keyword	Signal processing Sonar applications Dolphins Acoustic beams Satellite broadcasting Acoustic signal detection Biomedical signal processing Hardware Signal design Matched filters
Content Type	Text
Resource Type	Article

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