Abstract
Synthetic aperture sonar (SAS) interferometry is a powerful tool for
generating high resolution bathymetric maps. The basic principle of
interferometry is to relate the time-delay between echoes received by two displaced
sensors to a height. Cross-correlation and
phase-differencing are techniques used in SAS interferometry for
estimating time-delay, which both require the preceding processing steps
to be phase preserving.
Ground plane imaging is used to facilitate interferometry by reducing
geometrical distortions and
registering the sonar images.
This introduces a frequency shift to the images, which again reduces
the quality of the height estimate.
We propose a
deterministic and a statistical approach to compensate for this shift.
Both the deterministic and the statistic correction perform well on
both simulated test cases and on real data collected by the SENSOTEK
interferometric SAS during HUGIN trials. We also propose
the cross ambiguity function (CAF) as an alternative to
cross-correlation for estimating time-delay. The CAF method is better
suited for handling areas limited by geometric
distortions (or baseline decorrelation). CAF shows better performance
than cross-correlation, both on ground plane images from areas with
incorrect initial height, and on images of complex objects. This is
validated both on simulated test cases and on real data from SENSOTEK.