Abstract:
In practical applications with bathymetric sidescan sonars, the multipath reflections and
other directional interferences are the key limiting factors for a better performance. This
thesis proposes a new scheme to deal with the interferences using a multiple-row bathymetric sidescan sonar. Instead of smoothing the measurements over some time or angle
intervals, which was previously widely investigated, we resolve the multipath interferences from the direct signal. Two approaches on signal direction-of-arrival DOA and
amplitude estimation are developed, the correlated signal direction estimate CSDE for
three-row systems and the ESPRIT-based method. These approaches are compared using
different sonar data models, including a stochastic model from the statistical analysis on
bottom scattering and a coherent model from the analysis on interference field; the simulations show the ESPRIT-based approach is quite robust at the angular separation of 100
between two sources and at the signal-to-noise ratio above 10dB except for highly coherent or temporally correlated signals, for which CSDE works very well. The computer simulation results and the discussions on practical algorithm implementation indicate the
proposed scheme can be applied to a real multiple-row bathymetric sidescan sonar. With
the capability to simultaneously resolve two or more directional signals, the new sonar
model should work better for a wider variety of practical situations in shallow water with
out significant increase of the system cost.
