Spiral beacon calibration and experiments for underwater localization

Viegas, Rúben; Zabel, Friedrich; Gomes, João; Silva, António

http://hdl.handle.net/10400.1/26467

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Abstract(s)

Underwater localization and navigation are still challenging tasks due to the underwater acoustic channel characteristics. Spiral sources are underwater transducers that create structured acoustic fields from which the angle to the source can be readily obtained. The angle estimation is obtained from the phase difference between transmitted circular and spiral fields, but for reliable operation the transducers must be properly calibrated. This paper presents a spiral source calibration procedure with the integration of a stepper motor to measure phase and amplitude features of the transmitted circular and spiral fields, at multiple bearing angles. The calibration was performed for two developed prototypes, which in turn determined the most appropriate operating frequency range. For one of the prototypes, its linearity was confirmed at all the tested frequency ranges through homogeneity and additivity tests. In addition to calibration, acoustic localization experiments were carried out with the transmission of circular and spiral fields, with a comparative analysis against footage captured from the top of the test pool. The phase difference of the mobile hydrophone was subtracted to the phase difference of the reference hydrophone to compute the angle between the spiral beacon and the mobile hydrophone. The localization results revealed noteworthy angular errors, hypothesized to be associated with the Doppler effect induced by the movement of the mobile hydrophone. These calibration and localization experiments suggest that spiral sources could be an important enabling technology for safe and reliable localization of underwater vehicles.