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

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.

[1]  D. Jackson,et al.  High-Frequency Seafloor Acoustics , 2006 .

[2]  Armin W. Doerry,et al.  A SAR imaging model for large-scale atmospheric inhomogeneities , 2004, SPIE Defense + Commercial Sensing.

[3]  Hao Ling,et al.  Time-Frequency Transforms for Radar Imaging and Signal Analysis , 2002 .

[4]  R. Hanssen.  Radar Interferometry: Data Interpretation and Error Analysis , 2001 .

[5]  R.E. Hansen,et al.  High fidelity synthetic aperture sonar products for target analysis , 2008, OCEANS 2008.

[6]  Shen Chiu,et al.  A comparison of displaced phase centre antenna and along-track interferometry techniques for RADARSAT-2 ground moving target indication , 2005 .

[7]  Fuk K. Li,et al.  Synthetic aperture radar interferometry , 2000, Proceedings of the IEEE.

[8]  M.P. Hayes,et al.  Synthetic Aperture Sonar: A Review of Current Status , 2009, IEEE Journal of Oceanic Engineering.

[9]  Daniel C. Brown,et al.  The Impact of the Temporal Variability of Seafloor Roughness on Synthetic Aperture Sonar Repeat–Pass Interferometry , 2013, IEEE Journal of Oceanic Engineering.

[10]  M. Preiss,et al.  Coherent Change Detection: Theoretical Description and Experimental Results , 2006 .

[11]  F. Dickey,et al.  Degrading effects of the lower atmosphere on long-range airborne synthetic aperture radar imaging , 2007 .

[12]  C. D. Loggins,et al.  Measurement of the temporal phase stability of the medium , 1982 .

[13]  Charles Edward Muehe,et al.  Displaced-Phase-Center Antenna Technique , 2000 .

[14]  Michael P. Hayes,et al.  Measurements of acoustic phase stability in Loch Linnhe, Scotland , 1989 .

[15]  M. Soumekh.  Fourier Array Imaging , 1994 .

[16]  Kevin L. Williams,et al.  Effects of internal waves and turbulence on a horizontal aperture sonar , 1997 .

[17]  L. Brekhovskikh,et al.  Sound Propagation in the Random Ocean , 1982 .

[18]  Armin W. Doerry,et al.  Possible effects of clear-air refractive-index perturbations on SAR images , 2005, SPIE Defense + Commercial Sensing.

[19]  R. Beyer,et al.  Fundamentals of ocean acoustics , 1982 .

[20]  Charles V. Jakowatz,et al.  Spotlight-Mode Synthetic Aperture Radar: A Signal Processing Approach , 1996 .

[21]  Torstein Olsmo Sæbø,et al.  Wideband Interferometry in Synthetic Aperture Sonar , 2012, IEEE Transactions on Geoscience and Remote Sensing.

[22]  Torstein Olsmo Sæbø,et al.  Challenges in Seafloor Imaging and Mapping With Synthetic Aperture Sonar , 2010, IEEE Transactions on Geoscience and Remote Sensing.

[23]  K. Helfrich.  Internal solitary wave breaking and run-up on a uniform slope , 1992, Journal of Fluid Mechanics.

[24]  Isabelle Quidu,et al.  Change detection using Synthetic Aperture Sonar: Preliminary results from the Larvik trial , 2011, OCEANS'11 MTS/IEEE KONA.

[25]  Oliver B. Fringer,et al.  On the formation and propagation of nonlinear internal boluses across a shelf break , 2007, Journal of Fluid Mechanics.

[26]  D. L. Wilkinson,et al.  Run-up of internal waves on a gentle slope in a two-layered system , 1988, Journal of Fluid Mechanics.

[27]  D.A. Cook,et al.  Broadbeam multi-aspect synthetic aperture sonar , 2001, MTS/IEEE Oceans 2001. An Ocean Odyssey. Conference Proceedings (IEEE Cat. No.01CH37295).

[28]  R. Hansen.  Introduction to Synthetic Aperture Sonar , 2011 .

[29]  Riccardo Lanari,et al.  Synthetic Aperture Radar Processing , 1999 .

[30]  David M. Lane,et al.  Multiresolution 3-D Reconstruction From Side-Scan Sonar Images , 2007, IEEE Transactions on Image Processing.

[31]  Torstein Olsmo Sæbø,et al.  Seafloor depth estimation by means of interferometric synthetic aperture sonar , 2010 .

[32]  Dan E. Kelley,et al.  Evolution of a shoaling internal solitary wavetrain , 2007 .

[33]  J.E. Fernandez,et al.  Multi-aspect synthetic aperture sonar , 2000, OCEANS 2000 MTS/IEEE Conference and Exhibition. Conference Proceedings (Cat. No.00CH37158).

[34]  Kazuo Ouchi,et al.  On the multilook images of moving targets by synthetic aperture radars , 1985 .

[35]  A. Bellettini,et al.  Theoretical accuracy of synthetic aperture sonar micronavigation using a displaced phase-center antenna , 2002 .

[36]  Robert I. Odom,et al.  An Introduction to Underwater Acoustics: Principles and Applications , 2003 .

[37]  A. Currie,et al.  Synthetic aperture radar (SAR) images of moving targets , 1987 .

[38]  D. Massonnet,et al.  Imaging with Synthetic Aperture Radar , 2008 .

[39]  R. Keith Raney,et al.  Synthetic Aperture Imaging Radar and Moving Targets , 1971, IEEE Transactions on Aerospace and Electronic Systems.