Doppler effect on bathymetry using frequency modulated multibeam echo sounders

The latest generation of bathymetric multibeam echo sounders uses FM modulated signal with pulse compression in order to explore deeper seafloor while keeping a high resolution. Practically, the expected performances are not reached, and the first explanation made is this is due to the Doppler from the antenna motion which affects the FM signals processed with matched filtering. This paper describes and quantifies the impact of the Doppler effect on the bathymetry using FM and compares it with the narrow-band-signal case. Indeed, it is shown that Doppler impacts the FM signals after post-processing on two aspects: first a time shift due to the mismatch of the received dopplerised signal with the matched filter, second an error on the angular localisation.