Epipolar geometry of opti-acoustic stereo imaging

Optical and acoustic cameras are suitable imaging systems to inspect underwater structures, both in regular maintenance and security operations. Despite high resolution, optical systems have limited visibility range when deployed in turbid waters. In contrast, the new generation of high-frequency (MHz) acoustic cameras can provide images with enhanced target details in highly turbid waters, though their range is reduced by one to two orders of magnitude compared to traditional low-/midfrequency (10´s-100´s kHz) sonar systems. It is conceivable that an effective inspection strategy is the deployment of both optical and acoustic cameras on a submersible platform, to enable target imaging in a range of turbidity conditions. Under this scenario and where visibility allows, registration of the images from both cameras -arranged in binocular stereo configuration - provides valuable scene information that cannot be readily recovered from each sensor alone. In deriving the mathematical equations for 3D scene reconstruction, we address the epipolar constraint and stereo triangulation for these two imaging modalities with different projection geometries. We further show that opti-acoustic stereo imaging can lend advantages over traditional binocular vision with optical cameras.