Illustration of the parameterization used for the phase screen modelling. (a) Extract from the swath bathymetry compilation of Keeton (1997) showing the profile (red solid line) to be modelled. The red dotted line shows the area of seabed included in the modelling. (b) Rotated bathymetry grid to be input to the model (red dashed area from a). (c) 3-D representation of the input model, showing the seabed (bold black solid line) and the location of the horizontal screens (thin solid lines). (d) The velocity and density are defined on a regular grid of nodes on each screen where, in this example, the water column P-wave velocity (blue) is 1480 m s⁻¹, while the sub-seabed P-wave velocity (pink) is 3000 m s⁻¹.