Rapid developments in the search for means to provide detailed seabed mapping has led to the introduction of the Bathymetric Side Scan Profiling Sonar (BSSPS) System, which uses a two-transducer interferometer to map seabed features. Error in the resolved relative phase of the BSSPS system has crippled its application for resolving very detailed seabed features. This present work is concerned with the study, analysis and evaluation of the sources contributing to the system relative-phase error. Most of the sources of noise contributing to the relative-phase error can be prevented or reduced by good instrumentation and careful design, except the glint and the newly introduced source of noise, sliding ladder (SL). These sources were found to be unavoidable and cannot be eliminated, being part of the backscattered signal. Glint is only influenced by the angle of incidence, y, transducer separation, d, and pulse duration t. Sliding ladder noise is influenced by the grazing angle, e, (angle of reception relative to the boresight), pulse duration, t, and transducer separation, d. Reducing t has the effect of slightly reducing the relative-phase error due to glint, but greatly increasing it due to SL. Alternatively, reducing d has the effect of reducing the error due to both glint and SL, but it degrades the system resolving power. The choice of d and t is decided by the type of application and required resolution. This work also develops the design and implementation of the inverse tan method used to separate the relative-phase and envelope of the two received signals. The inverse tan method for resolving the relative phase (complex signal processor) is found to be simple, easy to implement, and accurate. In order to study the contribution and effect of the individual sources of noise on the relative-phase error, the BSSPS system was simulated. The designed computer model proved to be flexible, reliable and very useful. It was extensively used to test theoretical analysis as well as to achieve individual and collective glint and SL effects. Also the system was employed to test the influence of some of the system parameters on the sources of noise. Using the BSSPS simulated system we were able to provide some valuable guidelines for the sonar design and application concerning resolution, optimum mapped distance and an approach to reduce the relative-phase error (averaging). Applications of the present findings are not restricted to sonar systems, but would be just as useful to similar radar applications.
|Date of Award||1983|