Random refraction occurs in turbulence and through a wavy water-air interface. It creates distortion that changes in space, time and with viewpoint. Localizing objects in three dimensions (3D) despite this random distortion is important to some predators and also to submariners avoiding the salient use of periscopes. We take a multiview approach to this task. Refracted distortion statistics induce a probabilistic relation between any pixel location and a line of sight in space. Measurements of an object's random projection from multiple views and times lead to a likelihood function of the object's 3D location. The likelihood leads to estimates of the 3D location and its uncertainty. Furthermore, multiview images acquired simultaneously in a wide stereo baseline have uncorrelated distortions. This helps reduce the acquisition time needed for localization. The method is demonstrated in stereoscopic video sequences, both in a lab and a swimming pool.

Viewing an airborne scene from a submerged camera creates a virtual periscope, avoiding the saliency of a real maritime periscope. Random waves in the water-air interface severely distort the view, by refraction. We show a way to handle this. The distortion can be significantly countered, based on an estimate of the wavy water interface, at the instant of imaging. We obtain the interface estimate per frame, by a submerged sensor that simultaneously images the refracted Sun through an array of submerged pinholes. Our use of a stellar cue for estimation (and then correction) of the refractive field has analogy to ground-based astronomy. In astronomy, a guide star is imaged by a Shack-Hartmann sensor, for an estimate of the random refractive field created by atmospheric turbulence. In astronomy, this principle is used for countering blur, mainly by adaptive optics, while we use it for compensating distortions created by water waves. We introduce this novel concept for enabling a virtual periscope, demonstrate it, and analyze some of its limitations.

Random refraction occurs in turbulence and through a wavy water-air interface. It creates distortion that changes in space, time and with viewpoint. Localizing objects in three dimensions (3D) despite this random distortion is important to some predators and also to submariners avoiding the salient use of periscopes. We take a multiview approach to this task. Refracted distortion statistics induce a probabilistic relation between any pixel location and a line of sight in space. Measurements of an object's random projection from multiple views and times lead to a likelihood function of the object's 3D location. The likelihood leads to estimates of the 3D location and its uncertainty. Furthermore, multiview images acquired simultaneously in a wide stereo baseline have uncorrelated distortions. This helps reduce the acquisition time needed for localization. The method is demonstrated in stereoscopic video sequences, both in a lab and a swimming pool.

Spatio-temporal irradiance variations are created by some structured light setups. They also occur naturally underwater, where they are termed flicker. Underwater, visibility is also affected by water scattering. Methods for overcoming or exploiting flicker or scatter exist, when the imaging geometry is static or quasi-static. This work removes the need for quasi-static scene-object geometry under flickering illumination. A scene is observed from a free moving platform that carries standard frame-rate stereo cameras. The 3D scene structure is illumination invariant. Thus, as a reference for motion estimation, we use projections of stereoscopic range maps, rather than object radiance. Consequently, each object point can be tracked and then filtered in time, yielding deflickered videos. Moreover, since objects are viewed from different distances as the stereo rig moves, scattering effects on the images are modulated. This modulation, the recovered camera poses, 3D structure and de-flickered images yield inversion of scattering and recovery of the water attenuation coefficient. Thus, coupled difficult problems are solved in a single framework. This is demonstrated in underwater field experiments and in a lab.

Temporal irradiance variations are useful for finding dense stereo correspondences. These variations can be created artificially using structured light. They also occur naturally underwater. We introduce a variational optimization formulation for finding a dense stereo correspondence field. It is based on multi-frame optical flow, adapted to stereo. The formulation uses a sequence of stereo frames, and yields dense and robust results. The inherent aperture problem of optical flow is resolved using a temporal sequence of stereo frame-pairs. The results are achieved even without considering epi-polar geometry. The method has the ability to handle dynamic stereo underwater, in harsh conditions of flickering illumination. The method is demonstrated experimentally both outdoors and indoors.

Underwater, natural illumination typically varies strongly temporally and spatially. The reason is that waves on the water surface refract light into the water in a spatiotemporally varying manner. The resulting underwater illumination field is known as underwater caustics or flicker. In past studies, flicker has often been considered to be an undesired effect, which degrades the quality of images. In contrast, in this work, we show that flicker can actually be useful for vision in the underwater domain. Specifically, it solves very simply, accurately, and densely the stereo correspondence problem, irrespective of the object's texture. The temporal radiance variations due to flicker are unique to each object point, thus disambiguating the correspondence, with very simple calculations. This process is further enhanced by compounding the spatial variability in the flicker field. The method is demonstrated by underwater in-situ experiments.