The influence of ship motion on bathymetric sonar performance in FM mode of operation

The application of Frequency Modulated (FM) signals promises the following essential improvement of bathymetric sonar performance: (1) increase of swath width obtained because of the greater amount of energy radiated in the water, (2) better range resolution at long ranges caused by the independence between pulse length and spectral frequency pass-band, (3) possibility of multi-ping operation, and (4) better anti-interference features caused by matched filtering. While these benefits are attractive, there are additional constraints induced by the use of FM signals. The important factors that should be taken into account are ship motions (roll, pitch and yaw), ship speed, its trajectory and heading. All of these factors may worsen the performance so their effect on the system must be mitigated. The paper consists of two parts. In the first part we investigate the selection of FM parameters when motion and movement information is not available to the sonar system. In this case, the implementation of FM signals can be simplified but the benefit of this technology will not be maximum. The second part of the paper is devoted to the problem of efficiently using ship information to compensate for the Doppler Effect. This additional process will improve the system performances.