Underwater acoustic spiral source: pool tests and calibration

Underwater acoustic spiral sources are able to generate spiral acoustic fields where the phase depends on the bearing angle. It allows to estimate the bearing angle relatively to a receiver by subtracting the phases of a spiral and a circular wavefront, and can be used to estimate bearing angles with a single hydrophone/projector pair, e.g., for unmanned underwater vehicles localization. The developed spiral source comprises four monopoles/quadrants and it will be shown that the spiral source behavior is linear, which means that the generated acoustic signals are the sum of the four acoustic signals from each separate monopole, for any amplitude value. This work presents two calibration methods for spiral acoustic sources and the linearity evaluation for the used spiral source. Unlike the calibrations performed on signal reception, the two proposed calibration methods adjust the phase of the emitted signals to form the acoustic spiral field. The first calibration method rectifies the phase of one quadrant based on the contribution of the four quadrants. This method was tested and presented a performance lower than the performance of the calibration on the receiving side. After evaluating the linearity, a new calibration approach is suggested. This new approach uses the signals from separate quadrants instead of the contribution of the four quadrants. This method needs to be tested experimentally to check its validity.