Demonstration of spiral wave front sonar for active localization.

Spiral wave front sonar is a non-imaging, active sonar technique for remote target localization. It operates by transmitting a reference signal and a spiral signal whose phase varies by 2π over the transducer's azimuthal plane. Range is given by time-of-flight, and azimuthal aspect by computing the phase difference between reference and spiral echoes across a range of frequencies on a single receive channel. In addition, the spectral response of the target is available for classification algorithms. Two prototype spiral sonar systems (spiral transducer array, hydrophone receiver, amplifiers, and data acquisition) are tested in a series of laboratory experiments where fixed targets are tracked as the systems are rotated through 360°. The first prototype system uses an array designed for navigation and communications applications. This system demonstrates aspect errors less than 20° where shadowing of the receive hydrophone is not present. Experiments with a second system, utilizing transducers designed for higher frequency, active sonar applications, are performed in a bistatic scattering configuration. These experiments yielded errors less than 10° after calibration.