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 may become an outdated order thanks to a team of Technion-Israel  Institute of Technology researchers who have developed a new technology for  viewing objects above the waters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.

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