Experiments on a sonar with a synthetic aperture array moving on a rail

The application of synthetic aperture for sonars is hindered by the major difference between the celerity of acoustic waves for sonars and the celerity of electromagnetic waves for radars. This difference entails a greater sensitivity of signal processing to phase instabilities due to the inhomogeous medium or due to the unsteadiness of the sonar carrier. Nevertheless, the constant progress achieved in computing power, in the precision of inertial stations and in signal processing, should lead to sonars with synthetic aperture arrays in a near future. In that respect the first experiments conducted by GESMA are encouraging. The characteristics of the synthetic aperture are described, as well as the problems related to its application to the sonar field. The infrastructure of measurements, set up for the acquisition of data from a sonar with a synthetic aperture array, the motion of which is perfectly known, is described. The experimental results and a number of images obtained with real targets from the measurements are shown