Improving spatial resolution of interferometric bathymetry in multibeam echosounders

Most multibeam echosounders used in seafloor mapping use the interferometry method for bathymetry measurement, based on the zero‐crossing of the phase difference between two sub‐arrays. In this approach, only one sounding is computed per formed beam, and the spatial resolution is linked to the beam footprint extent. Using the whole content of the phase difference signal vs time makes it possible ideally to get a bathymetry data sampled at the very resolution of the digitised signal. A trade‐off is however to be found between this resolution improvement and the increase in the measurement noise. The performances of interferometric bathymetry are presented, together with the constraints of the resolution‐accuracy trade‐off, and a presentation of a high‐resolution algorithm for interferometric bathymetry applicable to multibeam systems. This is illustrated by results obtained on a wreck, showing the remarkable improvement achievable in resolution over a real target. The potentialities for this method are promising, since it allows to process, in the same beam, targets on the seafloor and inside the water column; simplifications in multibeam sounders array structure and processing are also to consider.