Virtual periscope is a system that allows submerged submarines to observe the surface above them without having to come to a shallower depth, as is required by traditional periscopes.
The system that was tested in 2005, actually described in a patent as "Virtual Periscope", aboard USS Chicago (SSN-721) employed a small camera mounted on the sail of the submarine uses the surface of the ocean as a lens, collecting light from above the surface and refracting it below. High-speed signal processing software assembles an image of what is on the surface. The system's resolution did not allow at the time ship identification, only indicating that something is on the surface. Objects 30 meters (100 feet) tall could be seen at about a distance of 1,600 meters (one mile). Sufficient light was available when a camera was positioned shallower than 30 to 60 meters (100 to 200 feet).
Stella maris
In 2014 Technion – Israel Institute of Technology researchers modeled a variant of virtual periscope on the image-processing technology used in astronomical observations to ameliorate the blur inherent in viewing stars through the atmosphere.
The technology behind Stella maris was disclosed to the public in a presentation at the IEEE International Conference on Computational Photography, held May 2–4, 2014 in Santa Clara, California. Associate Professor Yoav Y. Schechner of the Technion Department of Electrical Engineering explained the connection: