Pauline Vincent’s thesis work

Pauline Vincent’s thesis, funded by Kongsberg and co-supervised by Telecom-Bretagne, is directed at improving bathymetric performance achieved by multibeam echosounders using frequency-modulated signals. The first stage of research led to the conclusion that the observed deterioration in accuracy could not be explained by the Doppler effect alone. In 2012, Pauline Vincent worked on a more fruitful line of interpretation relating to the temporal structure of echoes obtained in FM mode. The basic idea is that the temporal wake of an echo signal generates a specific noise level in interferometer detection, related to the angular decorrelation of echoes. After conventional ‘pulse compression’ filtering, the temporal structure of FM signal echoes reveals secondary lobe interference, the presence of which offers an excellent explanation of the deterioration in bathymetric accuracy. This observation has been verified with experimental signals supplied by Kongsberg, digitally simulated signals, and with a theoretical model. The proposed solution involves modulating the FM signal envelope on transmission, a process which results in a significant decrease in the level of unwanted secondary lobes.