Implementation of adaptive and synthetic-aperture processing schemes in integrated active-passive sonar systems

Progress in the implementation of state-of-the-art signal processing schemes in sonar systems is limited mainly by the moderate advance made in sonar computing architectures and the lack of operational evaluation of the advanced processing schemes. Until recently, matrix-based processing techniques, such as adaptive and synthetic-aperture processing, could not be efficiently implemented in the current type of sonar systems, even though it is widely believed that they have advantages that can address the requirements associated with the difficult operational problems that next-generation sonars will have to solve. Interestingly, adaptive and synthetic-aperture techniques may be viewed by other disciplines as conventional schemes. For the sonar technology discipline, however, they are considered as advanced schemes because of the very limited progress that has been made in their implementation in sonar systems. This paper is intended to address issues of implementation of advanced processing schemes in sonar systems and also to serve as a brief overview to the principles and applications of advanced sonar signal processing. The main development reported in this paper deals with the definition of a generic beam-forming structure that allows the implementation of nonconventional signal-processing techniques in integrated active-passive sonar systems. These schemes are adaptive and synthetic-aperture beam formers that have been shown experimentally to provide improvements in array gain for signals embedded in partially correlated noise fields. Using target tracking and localization results as performance criteria, the impact and merits of these techniques are contrasted with those obtained using the conventional beam former.