On the modern high seas, raising your submarine's periscope at the wrong time is just as bad as raising a flag with a target on it. But thanks to a new optical suite developed by Israel's Technion Institute of Technology, tomorrow's subs will only ever have to break waves when in port.
The prototype technology, known as Stella Maris ("Stellar Marine Refractive Imaging Sensor" and an ancient navigational term for Polaris, the North Star) is essentially a "virtual periscope". It was unveiled at the IEEE International Conference on Computational Photography earlier this month in Santa Clara, CA by the Israeli team, led by Associate Professor Yoav Y. Schechner, of the Technion Department of Electrical Engineering.
Whereas conventional periscopes simply shove a long optical tube up through the waves, the Stella Maris instead employs a pinhole array, glass diffuser, and mirror set to generate images for the system's digital camera. Light shines through the pinholes and strikes the diffuser, which generates an image for the camera. This image is distorted by both the motion of the surface waves as well as the radical difference in refractive indexes between the water and air. To correct that distortion, the pinhole array also acts as a real-time surface level measure, gauging the height of waves as they pass over and feeding that information into an on-board computer which digitally corrects the image in real time. So instead of seeing the image on the left, you see the image on the right.
"Stella Maris is a novel approach to a virtual periscope as it passively measures water and waves by imaging the refracted sun." Schechner explained at the presentation, "When the water surface is wavy, sun-rays refract according to the waves and project onto the solar image plane. With the pinhole array, we obtain an array of tiny solar images on the diffuser."