New Looking Glass

Optics system technology would turn the ocean itself into a lens, enabling subs to perform some surface missions without a periscope.

By ROBERT A. HAMILTON, Special Correspondent

Since Simon Lake developed the U.S. Navy’s first periscope in 1902, there have been countless refinements, but one thing has remained unchanged: when a submarine wants to know what’s on the surface it has to poke up a mast.

On surveillance missions, that compromises its stealth, because the mast generates a radar return and creates a wake. And even on routine missions, coming shallow to use the periscope runs the risk of a sub surfacing under a ship it missed on sonar.

But submarines could soon get new optics systems that provide far greater stealth and security by allowing them to look around from the depths and without a mast due to two innovative products being developed by a small California company. The Virtual Periscope, slated for sea trials aboard the USS Chicago this summer, would turn the surface of the ocean itself into a lens. The Low-Cost Expendable Sensor (LCES) is a small tethered camera that would bob to the surface and send images back. Both systems have been developed by Areté Associates of Sherman Oaks, Calif.

“These devices have the potential to give us the first new optical sensors on a submarine since the periscope was invented,” said Nicholas Flacco, a senior scientist at Areté. “They’ll leverage the advantages of nuclear power by allowing you to stay deep as long as possible, and still know what’s happening on the surface. And they’re both very small, inexpensive sensors.”

These are envisioned as auxiliary optical systems rather than as potential replacements for conventional periscopes. Capt. David A. Portner, program manager for Submarine Sensor Systems at Naval Sea Systems Command, said both new systems have their limitations: they will rely heavily on signal processing to reconstruct fragmented images and, even under the best of circumstances, would only be able to look out two or three miles.

“But it would become another tool in the tool kit for the officer of the deck,” he said.

Portner said he would have loved to have had them on the submarine he commanded, the USS L. Mendel Rivers, which did a lot of special operations missions. He had to weigh the risk of exposing the ship against putting commandos into an unknown situation.

“We would have been able to conduct those operations without putting a periscope up,” Portner said.

Virtual Periscope takes advantage of the fact that the surface of the water acts as a rudimentary lens, collecting light from a semicircle above the surface and refracting it below. The system consists of a small camera mounted on the sail that would collect the light and use sophisticated signal processing software to assemble a picture of what is on the surface. The images might not be good enough to tell exactly what kind of ship is up there, but it would warn a submarine that there’s something in the way.

The deeper the submarine is, the wider the field of view would be and the further the horizon of its image is. In practice, however, the submarine would be limited to 100-200 feet below the surface before there’s insufficient light to use Virtual Periscope.

Areté first demonstrated Virtual Periscope in April 2001 in waters 10-40 feet deep off San Clemente Island, Calif. Since then it has improved the resolution of its images by a factor of more than four, and is nearing the point where it can detect a 100-foot-tall object at a nautical mile, or a 50-foot-tall object at half that distance.

U.S. Special Operations Command was sufficiently impressed with the results to sign an agreement in spring 2003 to pursue the technology for its swimmer delivery vehicles. The system would be undetectable from the surface, and take up very little space — it needs a domed rectangular housing of about 7-by-13 inches.

The LCES would be a camera on a buoy that could be launched from the 3-inch signal ejector. It would rise to the surface and send images back to the sub, where signal processors would assemble the images into a stable, 360-degree view of what’s above the ship. When the sub is done looking, it cuts the line and sails away.

“It’s like looking out a window — you’re going to have a good, rock-steady image of what’s at the surface,” Flacco said. “It’s much less detectable than a periscope. It sticks up about 3 inches from the surface of the water, and it will ride up on the waves, so it won’t leave a periscope wake, and it has virtually no radar signature. To anyone else, it will be bobbing around on the surface like a piece of trash.”

Portner said LCES would use largely commercial equipment, so it would be inexpensive, and send back undistorted images. But because it requires the use of the signal ejector there would be some loss of stealth.

Virtual Periscope would maximize stealth, but the algorithms needed to process the data it collects are complex, and improving the software to the point where the system is tactically useful is a challenge. Submarine Development Squadron 12 in Groton, Conn., is testing both concepts.

“Although we’re working on both of them, if we are able to make Virtual Periscope successful, I don’t think we’d really need the Low-Cost Expendable Sensor,” Portner said. But having the systems in concurrent development gives the submarine force a backup plan.

Meanwhile, the Navy’s Virginia-class submarines are being launched without the conventional lenses and prisms of traditional periscopes, according to a Navy statement. The subs will rely on electronic imaging equipment mounted atop photonics masts that telescope out of the sub’s sail. Images will be conveyed from the masts to two workstations and a commander’s console by means of a new fiber-optic system. This enabled sub designers to relocate the sub’s control room to the more commodious second deck.

Portner said the submarine force is taking additional steps to address shortcomings of the Type 18 periscope that has been in use for decades — the average age of a Type 18 is 25 years. The Navy has just awarded a contract to Kollmorgen for the Integrated Submarine Imaging System (ISIS) that will mount a digital camera at the top of the mast and send images via fiber-optic cable to a monitor in the control room.

“There are two advantages we gain from that,” Portner said. Not only does moving the camera to the top of the mast reduce the complexity of the periscope, eliminating a lot of moving optical parts that are subject to failure, it also eliminates any light loss within the optical barrel, increasing the time each day a periscope is useful in the visible spectra.

Portner’s office has also teamed with the NASA Jet Propulsion Laboratory in California to demonstrate 360-degree imaging with an array of cameras, about 7.5 inches in diameter, mounted on the mast.

“That would reduce the amount of time that the periscope has to be exposed, because in one second you’ll have a 360-degree view, rather than taking the time to move the periscope all the way around,” Portner said.

It would also free up space in the periscope shaft that would otherwise be devoted to the periscope handling system, and to the optics, space that could be filled with the electronics needed for real-time image processing, giving a much clearer picture of the operating environment, Portner said. And best of all, he noted, the hardware for ISIS and 360-degree imaging would also support Virtual Periscope and LCES.

“The ultimate goal for imaging is to get where … the hardware is all in place, and once a year or every two years we bring all-new capability in with a software refresh.”