Submarines: June 5, 2005

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The U.S. is experimenting with two new low-cost optics systems that would allow submerged submarines to "look" around at sea level without having to get close to the surface and raise a traditional periscope. These efforts also include an upgrade for existing periscopes by adding  a high-tech camera system. 

The Virtual Periscope will be tested aboard the USS Chicago this summer. It takes advantage of the fact that the surface of the ocean acts as a simple lens, collecting light from above the service and refracting it below. A small camera mounted on the sail of the submarine will collect the light and use high-speed signal processing software -- similar enhancement techniques used by NASA and government agencies for cleaning up blurred images -- to assemble a picture of what is on the surface. The images won't be good enough to identify what kind of ship type is above them, but it would be able to warn a submarine that there is something in the way on the surface. Virtual Periscope is good to about 100 to 200 feet below the surface before the light fades out and can spot a 30 meter tall object at about a distance of 1600 meters. U.S. Special Operations Command plans to put a smaller version of Virtual Periscope on its swimmer delivery vehicles. 

For cleaner pictures, the Low-Cost Expendable Sensor (LCES) using a small tethered camera on a buoy to bob to the surface to send images back. LCES can be deployed from the 76mm signal ejector and will ride above 3 inches above the surface to take pictures. Signal processing is used to assemble the images into a stable 360 degree view of what is above the ship. When finished, the line is cut and the sub can sail away. To an observer, the device looks like a piece of trash bobbing up and down on the surface, not a periscope. 

Each system has its drawbacks. LCES requires use of the signal ejector on the sub, so there is some noise emitted in deploying it. Virtual Periscope has no emissions, but the algorithms necessary to clean up the images are complex and need to be refined in order to make the system tactically useful. 

Both systems are the latest evolution away from the traditional fixed-mount periscope of conventional lenses and prisms. Virginia-class subs use electronics imaging equipment mounted on deployable masts that telescope upward out of the sail, with images transmitted down into the control room using fiber optics. Once transmitted, the images can be put up on large displays anywhere in the control room for anyone to examine. The Navy is also going to upgrade existing periscopes on older submarines to an integrated imaging system, mounting a digital camera at the top of the periscope and sending images via fiber-optic cable to a monitor in the control room. Moving the camera to the top of the mast gets rid of a lot of moving optical parts, increasing reliability. 

The Navy is looking into another upgrade to put an array of cameras onto the mast to provide a 360-degree view, again using some image processing to assemble the final result. Such a system would allow the Navy to free up precious space in the submarine that now goes to the pipes and hydraulics of the periscope handling system. Once in place, the camera and imaging hardware for the new system would also support both Virtual Periscope and LCES, so both features could essentially be added through software upgrades. Doug Mohney

 


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