From DefenseNews

 

Periscope Pursuit

New Breed of U.S. Navy Radars Would Reveal Stealthy Subs

By Jon W. Glass

Published: 17 November 2008

 

Trying to spot a submarine periscope lurking in cluttered coastal waters is akin to identifying a floating beer can from 60 miles away. That's the challenge the U.S. Navy faces as it tries to track a growing fleet of modern diesel-electric submarines.

 

The Pentagon plans to do this by improving existing radars with new signal processing software and by rotating the radar antennas faster inside their radomes. The Navy is moving forward to develop Automatic Radar Periscope Detection and Discrimination (ARPDD) radars for Nimitz-class aircraft carriers and anti-submarine MH-60R Seahawk helicopters. These helicopters are scheduled for deployment with the carrier USS John C. Stennis battle group in 2009, though they would not start carrying ARPDD radars until 2013.

 

ARPDD will capitalize on millions of dollars worth of research by the Navy and industry since the end of the Cold War to develop a radar capable of ferreting out periscope-like targets and automatically alert the operator to take a closer look.

 

One key will be the radar's ability to boost its scan rate from zero revolutions per minute (RPMs) when it is staring in one direction to make an image, up to a classified RPM for the new ARPDD mode.

 

Automation is another key. Current radar systems can discern small targets. However, they generate a high rate of false alarms in busy littoral waters, where it's easy to mistake small vessels, wind-whipped whitecaps and debris for the telltale signs of a prowling submarine. Radar operators must constantly monitor screens and manually sort through target hits, consuming valuable time.

 

The Navy wants to field the radar on the MH-60Rs by 2013 and install it on all Nimitz carriers by 2016.

 

"It's one of the fleet's top priorities," said Capt. Dean Peters, the MH-60R program manager for Naval Air Systems Command at Patuxent River, Md. "The Navy's focus has shifted from a deep-water type perspective to the littorals, where you would be more susceptible to diesel-electric submarines."

 

U.S. officials are wary of China, with its growing number of Song- and new Yuan-class diesel subs, and of Russia, maker of the diesel-electric Kilos. More unpredictable are threats from such nations as Iran, which owns at least three of the stealthy Kilo subs, and North Korea.

 

The hard-to-detect diesel-electric submersibles could wreak havoc in such strategic chokepoints as the Strait of Hormuz, the narrow oil-export channel in the Arabian Gulf, or the Strait of Malacca, the shipping lanes in Indonesia, said Pat Bright, a senior military analyst with AMI International, a Bremerton, Wash., company that analyzes naval markets.

 

While ARPDD's precise capabilities are classified, there's no secret behind what makes it work - it's all about algorithms, computer power and radar-signal processing.

 

The Navy is following separate tracks to get the upgraded radars on the carriers and the MH-60Rs. In June, the Navy awarded a $144 million design-and-development contract to Lockheed Martin Integrated Systems of Owego, N.Y., to incorporate the radars on the helicopters.

 

Lockheed Martin builds the cockpit and air weapon system for the Seahawks, and the company passed along $71.5 million to Telephonics, Farmingdale, N.Y., to upgrade its existing AN/APS-147 radar systems into ARPDD systems. The electronics and communications firm built the AN/APS-147 for the Seahawks.

 

"The vast majority of the change is going into the signal processor, where we will remove certain processors in the box today and replace them with higher-power processing and higher data throughput rates at faster speeds," Telephonics' President Joe Battaglia said.

 

Researchers at the Navy's China Lake weapon division in California developed the complex algorithms that underlie ARPDD's ability. The mathematical equations are bundled into computer software programs designed to enable the radar to pick out a submarine periscope from among the surface clutter. Off-the-shelf quad processors - four computers bunched onto a single circuit card - are being used to bolster the AN/APS-147's signal-processing power by eight times.

 

Eventually, the ARPDD radar system could be installed in other aircraft, including UAVs, with only "minor tweaks" to account for differences in flight profile, Battaglia said.

 

Technology breakthroughs in recent years have shrunk processors and increased computing speed - the same kind of advances seen in desktop home computers. Now, the system being designed for the MH-60R is the size of a large toaster oven and is light enough to be installed by one person, said Rich Holmberg, director of Naval Helicopter Programs at Lockheed Martin's Owego division.

 

Flight tests in the Seahawks are scheduled for late 2009. "We expect it's going to work like gangbusters," Battaglia said.

 

The Navy anticipates awarding a production contract in late 2010 or early 2011 and installing the upgrades on the first MH-60Rs in 2013, Peters said.

 

On the Seahawks, ARPDD is being designed to provide battlegroups with wide-area submarine surveillance from a typical cruising altitude of about 7,000 feet and well beyond 60 nautical miles from potential targets. Visual cues built into the system will alert an operator when periscopelike objects are detected. The crew could then swoop down to 100 feet and use dipping sonar or sonobuoys to confirm a submarine's presence, Holmberg said.

 

"From the Navy's point of view, anti-submarine warfare probably is the most important mission to get right because the biggest problem for them is under the sea," said Owen Cote, associate director of MIT's Security Studies Program.

 

For the carriers, ARPDD evolved into a program known as the AN/SPS-74 CVN Periscope Detection Radar. Mounted on the mast of a carrier, the radar antenna would be less effective at longer ranges, offering more of a "terminal" defensive system, Cote said.

Very difficult matters to simulate in our HCE, I fear !

Very difficult matters to simulate in our HCE, I fear !

 

Thats true. Thus far, at least. But it does highlight the danger in running with your scope up, or alternatively, the value of a good helicopter borne surface search radar.