Optics Near the Snell Angle in a Water-to-Air Change of Medium

Abstract

Underwater imaging of the air environment is described with particular attention given to the optical problems of nearhorizon viewing. These include severe chromatic aberration from transmission through the seawater wedge, the horizon distortion effect, and anisoplanatism resultingfrom the change of refractive aberrations in different areas of view. Various optical designs or schemes are presented that correct or relieve thefirst two optical problems. Strategies to minimize or attempt to view through the varying refraction ofthe surface are also suggested, and one is investigated.

STELLA MARIS: Stellar marine refractive imaging sensor

“…Distortions can be reduced significantly using this physics-based method, but uncertainties pointed theoretically leave residual distortions. Nevertheless, images corrected by our process can later be handled by statistical un-distortion post-processes [26,29,47,48,50], such as lucky imaging [8,9,44], stochastic triangulation [2], and motion detection [1]. Rather than facing the full-blown distortions in raw images, such video post-processing methods may handle more easily images whose distortions are residual.…”

“…Images taken this way suffer severe refractive distortions, even if the water-air interface (WAI) is flat [2,35]. For distant objects, distortions attributed to flat-water can be countered by optical and computational methods [44]. Random waves of the WAI greatly exacerbate the distortions.…”

Triangulation in Random Refractive Distortions

“…Lucky imaging [14,15,46,55] require a large number of frames, out which a best-representative frame is selected per patch. Less temporal frames are needed if a spatiotemporal distortion model [34,35,51] is fitted to the image data, or given an undistorted template image [52].…”

Detecting Motion through Dynamic Refraction

“…Distortions in oblique view through a flat WAI were thoroughly analyzed [10], [20], [36], [47]. Suiter et al [43] introduce optical elements to the camera, to correct for flat WAI distortion. Our conclusion is that if a flat WAI is the only distortion source, then this distortion can be compensated for using stereo [10].…”