Thanks Don S.
Sunday, June 08, 2014
The non-periscope periscope from Israel
Prof. Yoav Schechner, of the Technions electrical engineering department, and colleagues developed the virtual periscope.
Tekumah, a Dolphin-class submarine, is capable of carrying nuclear warheads. Photo: REUTERS
Up periscope! may become an outdated order thanks to a team of Technion-Israel Institute of Technology researchers who have developed a new technology for viewing objects above the waters surface without the need for a periscope poking its head above the waves. The researchers modeled their virtual periscope on technology used by astronomers to counter blurring and distortion caused by layers of atmosphere when viewing stars.
The technology behind a submerged virtual periscope was introduced in a presentation at the IEEE International Conference on Computational Photography, held in California earlier this month. Prof. Yoav Schechner, of the Technions electrical engineering department, and colleagues developed the virtual periscope, which is called Stella Maris (Stellar Marine Refractive Imaging Sensor).
The heart of the underwater imaging system is a camera a pinhole array to admit light (a thin metal sheet with precise, laser-cut holes), a glass diffuser and mirrors.
The rays of the sun are projected through the pinholes to the diffuser, which is imaged by the camera, beside the distorted object of interest. The image is then corrected for distortion.
Raw images taken by a submerged camera are degraded by water-surface waves similarly to degradation of astronomical images by our atmosphere. We borrowed the concept from astronomers who use the Shack-Hartmann astronomical sensor on telescopes to counter blurring and distortion caused by layers of atmosphere, explained Schechner. Stella Maris is a novel approach to a virtual periscope as it passively measures water and waves by imaging the refracted sun.
The unique technology gets around the inevitable distortion caused by the water-surface waves when using a submerged camera.
According to the Technion engineer, because of the sharp refractive differences between water and air, random waves at the interface present distortions that are worse than the distortion atmospheric turbulence creates for astronomers peering into space.
When the water surface is wavy, the suns rays refract according to the waves and project onto the solar image plane, said Schechner. With the pinhole array, we obtain an array of tiny solar images on the diffuser.
When all of the components work together, the Stella Maris system acts as both a wave sensor to estimate the water surface, and a viewing system to see the above-surface image of interest through a computerized, reconstructed
The Stella Maris virtual periscope is just the latest technology developed by the researchers, who have also found ways to exploit underwater flicker random change of underwater lighting caused by the water surface wave motion. The team turned the tables on underwater flicker and used the natural rapid and random motion of the light beams to obtain three-dimensional mapping of the sea floor.
The virtual periscope may have other potential uses in which they could reduce the reliance on traditional periscopes, that have been in use for more than a century.
Submerged on the sea floor, Stella Maris could be useful for marine biology research when viewing and imaging both beneath and above the waves simultaneously is important. It could, for example, monitor the habits of seabirds as they fly, then plunge into water and capture prey.
There are many ways to advance the virtual periscope, says Schechner, who adds that while the system requires sunlight, they are currently working on a way to gather enough light from moonlight or starlight to be able to use the system at night.
Thanks Don S.