Motion-Compensated Acoustic Positioning in Very Shallow Waters Using Spread-Spectrum Signaling and a Tetrahedral Ultrashort Baseline Array
Ultrashort baseline acoustic positioning systems (APSs) are well suited for unmanned underwater vehicle operations because of their small space requirement and ease of deployment. This type of positioning system estimates the relative phases between signals measured by an array of transducers, each a half wavelength from the others. The accuracy of these relative-phase estimates is limited by several factors. Reverberation may cause major signal distortion in the acoustic signals received by the array and limit the accuracy of time-delay estimation during position estimation. Another limiting factor is the ambient noise present in shallow and deep waters generated by waves, rain, boat traffic, and biological life. A motion-compensated ultrashort baseline APS operable in shallow water and port environment has been implemented at Florida Atlantic University. Multitones signal modulation and log-likelihood maximization enable this APS to operate in highly reverberant environments. The motion compensation system estimates the array position and orientation by merging inertial and differential GPS measurements using Kalman filtering techniques. Experiments show 0.67 and 2.67 degrees of error for the array tilt and heading estimates and 0.74 m for the array position estimate at a range of 23 m.
Document Type: Research Article
Publication date: September 1, 2010
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