Refractive geometry for underwater domes

Underwater cameras are typically placed behind glass windows to protect them from the water. Spherical glass, a dome port, is well suited for high water pressures at great depth, allows large field of view, and avoids refraction if pinhole camera positioned exactly sphere's center. Adjusting real lens perfectly center challenging task, both in terms how actually guide centering process (e.g. visual servoing) measure alignment quality, but also, mechanically perform alignment. Consequently, such systems prone being decentered by some offset, leading patterns sphere that invalidate model. We show overall system becomes an axial camera, even thick domes as used deep sea exploration provide non-iterative way compute without requiring knowledge exact air, or properties. also analyze refractive geometry sphere, looking effects forward- vs. backward decentering, iso-refraction curves obtain 6th-degree polynomial equation forward projection 3D points thin domes. then propose pure underwater calibration procedure estimate decentering multiple images. This can either be during adjustment mechanical position lens, considered photogrammetric applications.