Improving spatial resolution of interferometric bathymetry in multibeam echosounders

International audienceMost multibeam echosounders used in seafloor mapping perform 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 to ideally get a bathymetry data sampled at the very resolution of the digitized signal. However, this approach compels the phase difference to be unambiguous. Indeed, when the phase difference is determined through the argument operator, the resulting value is truncated within a 2pi-length interval. To tackle this hitch, this paper presents and compares techniques to remove the phase ambiguity based upon interferometry, cross correlation and high-resolution methods. Figures are illustrated by results obtained on a shipwreck, enhancing the difficulties of each removal technique