Finally - Underwater GPS

[MrTShirt]

For your Christmas tree, a technique for navigation underwater to an accuracy of 61 km.

Prof. Viktor Gruev, Univ of Illinois developed a camera that mimics the eye of the mantis shrimp and uses polarization patterns that correlate with the sun's position.  Add time and you have earth coordinates.

Ref:  Photonics & Imaging Technology, Nov. 2018, p16.