A Motion Compensated (MC) Ultra Short Baseline (USBL) Acoustic Positioning
System (APS) operable in shallow water and port environment has been implemented at
Florida Atlantic University. Multi-tones signal modulation and log-likelihood
maximization enable this APS to operate in volumes of water of less than 10 cubic
meters. Standard deviations of the acoustic source elevation and azimuth estimates were
computed to be 3 degrees in an 8 cubic meters test tank, and reduce to 0.9 degree in a 2
meters deep marina. The motion compensating system estimates the array position and
orientation while merging noisy measurements from a Magnetic, Angular Rate, and
Gravity (MARG) sensor and a Differential Global Positioning System (DGPS) using
Kalman filters. Experiments show 0.67 and 2.67 degrees of error for the array tilt and
heading estimates, and 0.74 meter for the array position estimate.