2023_programme: Resampling of bathymetric data for SAS processing

• Session: 15. Towards Automatic Target Recognition. Detection, Classification and Modelling
  Organiser(s): Johannes Groen, Yan Pailhas, Roy Edgar Hansen, Jessica Topple and Narada Warakagoda
• Lecture: Resampling of bathymetric data for SAS processing [invited]
  Paper ID: 1922
  Author(s): Bonnett Blair, Schmaljohann Holger, Fickenscher Thomas
  Presenter: Bonnett Blair
  Abstract: Generating SAS images involves delaying and coherently summing the echoes recorded by the elements of the receiving array over multiple pings onto the desired rendering points. This requires accurate knowledge of the two-way travel time taken by the signal to travel from the transmitter to a particular point and the echo to return to each physical receiving element at each ping within the synthetic aperture. The bathymetry of the scene has a significant impact on the two-way travel time which cannot be ignored. Inaccuracies in the assumed bathymetry, e.g., an incorrect height, lead to errors in the estimated travel time and cause defocusing of the image. If prior information of the bathymetry is available, it can be used to improve the estimate of the travel time. Typically it is desired to form the image on a grid with a regular sample spacing. However, the bathymetric data may not be regularly sampled. For example, our processing chain generates a pair of sidescan images using broadside beamforming with vertically separated receiver arrays to estimate the bathymetry via interferometry. Due to the non-ideal motion of the vehicle, the broadside beams are neither parallel to each other nor equally spaced. This effect is particularly pronounced when used with a circular geometry: bathymetric estimates will be dense in the centre of the circle and sparse near its circumference. There may also be gaps in the estimates due to shadows, area of low coherence, crabbing etc. Data captured externally (e.g., from an echo sounder, or on a prior mission) may be in a different coordinate system to the current mission. In this paper, we compare two methods for resampling the bathymetric measurements to an imaging grid, namely linear barycentric interpolation and IDW interpolation.
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• Corresponding author: Dr Blair Bonnett
  Affiliation: Helmut-Schmidt-Universität
  Country: Germany
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