Improved real-time adaptive multi-sonar controller

Abstract

In this thesis an adaptive automatic controller which precisely synchronizes the pinging sequence of multiple sonar devices is described. The acquisition and fusion of multiple datasets from the same seabed region has been proved to afford a better data analysis and interpretation, while their combined analysis provides complimentary information that helps resolving ambiguities upon the studied data. Moreover, the concurrent collection of datasets reduces the survey time and cost. The interest of this study is the design, development and validation of a system which allows the simultaneous operation of multiple high-frequency sonars. It employs previously acquired bathymetric data (multiple depth measurements) to generate geo-referenced Digital Terrain Model

data-subsets on the fly. These are subsequently used to accurately predict the transmission- reception timing of the payload sensor acoustic pulses by finding the intersection of the outer part

of their beams with the previously explored terrain. The distance from the devices to their corresponding intersections are translated into travel time values. Using these times, the controller synchronizes the trigger of the instruments in a non-interfering fashion. In addition, it reduces the errors in the calculations normally associated with sensor misalignments and platforms movements. The controller is transparent and modular (object-oriented), thus enabling ease of integration with the existing systems and facilitating test, upgrade and/or change of different system modules independently. Tests and simulations were carried out to evaluate the scheduler system performance. In most cases, the algorithm can handle the maximum theoretically achievable ping rate imposed by the device beam geometries. However, if the computational time exceeds a threshold, the ping rate is reduced accordingly. As a consequence of this ping rate reduction the platform speed must be reduced to maintain required survey resolution.