Change detection using Synthetic Aperture Sonar: Preliminary results from the Larvik trial

Abstract

In April of 2011, FFI led a sea trial near Larvik, Norway on FFIs research vessel the H.U. Sverdrup II with participation by representatives from Canada, United States, and France. One objective of the sea trial was to acquire a data set suitable for examining incoherent and coherent change detection and automated target recognition (ATR) algorithms applied to Synthetic Aperture Sonar (SAS) imagery. The end goal is to produce an automated tool for detecting recently placed objects on the seafloor. To test these algorithms two areas were chosen, one with a comparatively benign seafloor and one with a boulder strewn complex seafloor. Each area was surveyed before and after deployment of objects. The survey time intervals varied from two days to eight days. In this paper we present the trial and show examples of SAS images and change detection of the images.

Measurements of high-frequency acoustic scattering from glacially eroded rock outcrops

“…The change in sound speed of the lower 10 m of the water column was a maximum of 3 m/s, and therefore refraction effects on the local grazing angle can be ignored. Further details on the experiment can be found in Midtgaard et al (2011).…”

“…These outcrops contain two contrasting roughness characteristics that allow model-data comparisons to be made under different conditions. Acoustic backscattering data at 100 kHz were collected off the coast of Sandefjord, Norway by the Norwegian Defence Research Establishment (FFI) aboard the HU Sverdrup II using the HISAS 1030 synthetic aperture sonar (SAS) system from a HUGIN autonomous vehicle (Midtgaard et al, 2011;Fossum et al, 2008). This sonar has not been calibrated in terms of its receiver sensitivity s r or source strength s 0 , which are required for scattering strength estimates.…”

Image registration of simulated synthetic aperture sonar images using SIFT

“…For automatic change detection, Midtgaard et al [14] preprocess the image using anisotropic diffusion, find SURF feature correspondences, and compute an affine transformation. G-Michael et al [6] use SIFT for initial coarse registration, using the correspondences to estimate a 2D image shift (no rotation or scaling).…”

Synthetic Aperture Sonar Technology Review

“…A critical success factor for repeat pass processing is accurate data acquisition and control, which again imposes strict requirements on vehicle control and navigation accuracy. Another critical success factor is data-driven coregistration of the SAS images in repeated passes (Midtgaard et al, 2011;Saebø et al, 2011;Sternlicht et al, 2012).…”