The Effect of Internal Wave-Related Features on Synthetic Aperture Sonar

Author
Hansen, Roy Edgar
Lyons, Anthony P.
Sæbø, Torstein Olsmo
Callow, Hayden John
Cook, Daniel A.
Date Issued
2015
Permalink
http://hdl.handle.net/20.500.12242/730
https://publications.ffi.no/123456789/730
DOI
10.1109/JOE.2014.2340351
Collection
Articles
Description
Hansen, Roy Edgar; Lyons, Anthony P.; Sæbø, Torstein Olsmo; Callow, Hayden John; Cook, Daniel A.. The Effect of Internal Wave-Related Features on Synthetic Aperture Sonar. IEEE Journal of Oceanic Engineering 2015 ;Volum 40.(3) s. 621-631
1264117.pdf
Size: 5M
Abstract
In October 2012, the Centre for Maritime Research and Experimentation (CMRE, La Spezia, Italy) conducted trials from the NATO research vessel (RV) Alliance, off Elba Island, Italy. During this trial, data were collected by the Norwegian Defence Research Establishment (FFI, Kjeller, Norway) using a HUGIN autonomous underwater vehicle (AUV) with interferometric synthetic aperture sonar (SAS) in repeated passes. Large linear structures (tens of meters by several meters) observed in both the SAS images and SAS bathymetry during the initial pass were absent in data taken on a repeated pass the following day. We suggest that these phenomena were not true seafloor features, but were caused by features in the water column, known as boluses, which can form after breaking internal wave events. The changes observed in acoustical intensity and phase appear to be caused by the interaction of the acoustical field with the lower average sound-speed structure of the bolus, constructing features in both SAS imagery and SAS bathymetry that looked like seabed topography. In this paper, we present examples and give an interpretation of the results based on an acoustical ray model. We discuss different techniques for recognizing these phenomena: repeat pass imaging and interferometry, multilook and multiaperture processing, and moving target analysis.
View Meta Data