Sensor fusion and advanced computers are common links in detection of sea and land mines
By John Rhea
True, the Cold War as we knew it might be over, but many of the same military challenges remain. Today`s headlines reflect a litany of military threats that are far different and sometimes even more lethal than those the U.S. and its allies faced when NATO and Warsaw Pact forces glowered at one another over the Berlin Wall. One continuing threat comes from ever-more-sophisticated explosive mines on land and at sea, and the need to find and destroy these mines is spawning a host of new technologies.
Yet even though an extensive assortment of sensor and computational technologies is available for countering land and sea mines, the crucial factor in each case is integrating these technologies into operational systems. Since the data necessary for mine detection come from a variety of heterogeneous sources, this puts a high premium on sophisticated sensor-fusion techniques.
"No single technology will satisfy all the requirements," says Bill McNary, business development manager for advanced systems at Sanders, a Lockheed Martin company in Nashua, N.H. "What we need is a suite of capabilities."
In the case of land mines, sensor capabilities tend to combine infrared for finding the mines and microwave imaging and magnetic detectors for classifying them. Designers of sea-based mine detectors, who generally build systems that revolve around acoustic sensors, are showing a new interest in lasers to pinpoint the locations of underwater mines at different depths. These designers are keenly aware they must craft systems that not only can locate metallic mines, but non-metallic mines as well.
Sanders has a foot in both camps. Sanders engineers compete for the U.S. Navy`s Advanced Laser Mine Detection System (ALMDS), which will use commercially available lasers mounted in a helicopter pod to scan the ocean surface and look for subsurface reflections to find mines. Sanders also is a subcontractor to Jaycor in Albuquerque, N.M., on the U.S. Army`s Vehicle Mounted Mine Detection (VMMD) system, which will use forward-looking infrared (FLIR) and ground-penetrating radar.
VMMD is an example of how state-of-the-art technologies combined with sensor fusion give the Army a tactical capability to detect land mines while ground forces are on the move, adds Ron Kelly, Jaycor vice president. The FLIR from Lockheed Martin`s Electronics and Missiles Division in Orlando, Fla., is what he calls a standoff sensor capable of looking five to 30 meters ahead. The ground-penetrating radar adds an all-weather capability. Integrating the sensor inputs is a commercially available Sun workstation on board Army vehicles.
Experts have field tested the VMMD at Fort A.P. Hill, Va., using a commercial Hummer vehicle. Kelly points out the requirement is for compatibility with all Army vehicles, including the High Mobility Multi-Purpose Wheeled Vehicle (HMMWV) and commercial vehicles, "even Toyota pickup trucks." The Night Vision Laboratory at Fort Belvoir, Va., sponsors the three-year demonstration project begun last year. The Night Vision Lab is part of the Army`s Communications-Electronics Command at Fort Monmouth, N.J.
Despite the initial success at Fort A.P. Hill and at the New Mexico Institute of Technology`s instrumented range at Socorro, N.M., Kelly says his engineers still need more research. "I`m not ready to drive this through a mine field," he comments.
Another futuristic project at Sanders is what company engineers call the Audrey system, a set of microwave imaging detectors that look for non-metallic mines and operate autonomously over the battlefield. Although this project is in the proof-of-concept stage, McNary says Audrey detected anti-tank mines in recent tests.
The goal, he says, is to use machines to find the smaller and more-elusive anti-personnel mines without putting soldiers at risk. Most people, after all, still identify mine-hunting with the image of terrified soldiers on hands and knees gingerly picking their way through minefields with bayonets with its inevitable tragic mishaps. This is why the research is focusing on autonomous and teleoperated systems. Audrey is not a military designation; the system got its name because engineers thought it looked like the man-eating plant of that name in the movie "Little Shop of Horrors."
Looking for mines is a computationally intensive task particularly for small anti-personnel land mines that most often are scattered in hard-to-detect patterns, McNary points out. He envisions the use of such advanced computing techniques as artificial neural networks. But the basic computational capability is readily available from the principal producers of computers able to perform sensor fusion, such as CSPI in Billerica, Mass., and Mercury Computer Systems and Sky Computers Inc., both in Chelmsford, Mass.
Showing the computational intensity of this task, Russell Adamchak, director of business development at Mercury, notes that today`s land mine is smaller than a coffee cup and frequently made of plastic, which infrared sensors cannot readily detect.
Sea mines, meanwhile, are a different challenge, he adds. They are about two or three feet in diameter, but are no longer the "dumb" floating mines of World War II vintage; they can lie on the bottom of the ocean for a long time waiting for an acoustic signal or the magnetic field of a passing ship to trigger them. "It only takes one mine to ruin your day," Adamchak quips.
Furthermore, the constant danger of mines is forcing military leaders to change their approach to mine detection. Land mines, for example, continue to be a threat in places such as Bosnia and Kosovo. U.S. Navy leaders, who are playing an increasing role in support of ground forces, are concerned with the danger of sea mines in the shallow water areas adjacent to coastlines. The old method of using a dedicated mine warfare unit on call to help units in combat is becoming obsolete, Adamchak points out. "It takes too long to get there," he says.
Instead, the military services are turning to what is known as the organic approach, in which combat units themselves handle counter-mine assets and perform their functions as part of an ongoing military operation. Organic unit organization should be able to reduce the time necessary for counter-mine forces to find and clear mines for deployed naval forces, says Ken Haas, an assistant program manager for airborne mine defense systems in the Navy`s mine warfare program office. This would require organic counter-mine forces to:
- determine if mines are a threat;
- identify which areas pose the greatest danger from mines; and
- support dedicated anti-mine units if commanders on the scene decide they are necessary.
This approach also puts a premium on light, sophisticated electronic systems, and this is where advanced technologies can make a major contribution. The Navy`s present airborne mine countermeasures (AMCM) forces are built around the Sikorsky MH-53E Super Stallion helicopter one of the largest rotorcraft in the U.S. inventory. These aircraft require substantial logistics support and lots of space aboard ship, Haas notes.
Instead, Navy leaders are looking to the smaller multi-purpose Sikorsky CH-60 Seahawk combat-support helicopter, which could shoulder a large part of the counter-mine job with miniaturized equipment. Navy leaders say they hope the CH-60 will complement and eventually replace the current force of aging twin-rotor CH-46 Sea Knight helicopters for search and rescue, special operations, and logistics, as well as for airborne mine countermeasures.
Haas outlines a Navy deployment program as follows. First, the program would begin with today`s Navy helicopters and perhaps switch later to a new helicopter (either the H-60 class or the international EH-101). The program would proceed with a series of small, light AMCM systems, that would include the AN/AQS-20 airborne mine hunting sonar that engineers at the Raytheon Systems Co. in Sudbury, Mass., are producing. Part of this phase would be the shallow-water influence minesweeping system (SWIMS) under contract to EDO Corp.`s Marine and Aircraft Systems facility in North Amityville, N.Y.
The AN/AQS-20 is a helicopter-towed system for high-speed reconnaissance and mine hunting to detect, classify, and localize unburied bottom, close-tethered, and moored mines. SWIMS is a high-speed magnetic and acoustic mine-sweeping system to support shallow-water mine clearance prior to amphibious operations. EDO won a $9.6 million Navy contract for production of SWIMS in March, and deliveries are due to begin next year.
Advanced electronics, meanwhile, are extending the life of a mainstay of the Navy`s counter-mine operations the AN/AQS-14 side-scan sonar system that can be towed behind the MH-53E helicopter, surface ships, or remotely controlled tow craft. This system makes extensive use of commercial off-the-shelf, or COTS, hardware in the "topside," or helicopter portion, such as VME chassis and standard video monitors. The towed vehicle, or "fish," uses custom boards because of the constraints of its 10.5-inch diameter.
Experts are upgrading the AN/AQS-14 by installing modification kits, says Joe Davis, marketing manager at the system`s prime contractor, Northrop Grumman Corp.`s Oceanic Systems business unit in Annapolis, Md. Shipments are due to begin by the end of this year to helicopter minesweeping units in Norfolk, Va., and Corpus Christi, Texas. These involve digitally programmable beam formers and data links for real-time capabilities. COTS boards power a new navigation and acoustic control processor.
Designers are implementing a new laser mine identification capability in the towed vehicle, which is based on commercial lasers previously used to search for wrecked aircraft on the ocean bottom. Davis says these lasers provide "almost photographic quality." These neodymium-YAG continuous-wave lasers operate at 532 nanometers and are available off the shelf from Coherent Technologies of Lafayette, Colo., explains Gene Cumm, an engineering manager at the Annapolis facility. Cumm says these lasers provide images that are 36 times better than sonar.
Another feature of the AQS-14 is post-mission analysis, where experts analyze digitally recorded mission tapes to provide computer-aided detection and classification of contacts. This feature includes the ability to freeze frames for analysis, enlarge objects, and compare objects with known objects in a database.
Navy leaders have an evolutionary sequence of counter-mine programs in progress to achieve an organic capability for deployed naval forces using unmanned undersea vehicles (UUVs). The Northrop Grumman Annapolis facility has the Near-term Mine Reconnaissance System (NMRS), which involves a UUV to be launched from a submarine to provide real-time high-resolution sonar data. The company`s design evolved from its experience in the torpedo business. The challenge was to pack the sensor package into a 21-inch-diameter tethered vehicle. Company officials say they were able to accomplish this with 75 percent COTS hardware and software.
Northrop Grumman officials have delivered an NMRS system that demonstrated the feasibility of the concept, and it should become operational by around 2003. However, Navy officials are preparing for a follow-on system the Long-term Mine Reconnaissance System (LMRS). This is an untethered UUV that could be launched from a submarine or surface ship and operate autonomously for about eight hours in shallow water. Navy leaders are scheduled to select a prime contractor for LMRS this fall, and NMRS represents an interim capability in the Navy`s quest for stealthy counter-mine operations.
Army leaders also are taking steps to achieve an organic counter-mine capability, as outlined in a Pentagon briefing by Col. David Kingston, director of combat development at the Army Engineer School at Fort Leonard Wood, Mo. Kingston, who served for eight months in Bosnia where he supervised mine-clearing operations, says mine countermeasures center on an engineer battalion of normally about 412 soldiers that is part of a brigade combat team a combined-arms organization of 3,000 to 5,000 soldiers.
In Bosnia the Army set up a special mine action center to counter what he called a "very, very high mine threat environment" of between 3 million and 5 million land mines, some metallic and some "with very, very low metallic content." Out of this experience came a better definition of the processes involved in counter-mine operations, he says. "They include such things as breaching, clearing, marking, reporting, and also force protection aspects of U.S. forces as we work in this environment.
"The soldiers had extremely good situational awareness because we set up these mine action centers where we basically got all the mine field data we could get our hands on, sorted it out, packaged it, and sent it back out so that all the soldiers had that situational awareness," he explains. "That was definitely one of the good lessons learned out of Bosnia."
Kingston also makes the distinction between counter-mine operations that support military operations, and what he calls humanitarian de-mining operations. While most of the current development focuses on immediate military needs, affordable technologies will also be necessary to counter the danger to civilians. A 1996 UNICEF report estimated that 110 million land mines were strewn throughout 64 countries, endangering civilians as well as military troops. Many of these mines were activated during conflicts long since resolved. Yet the devices, often costing as little as three dollars apiece, still pose a serious threat.
The U.S. Army`s Vehicle-Mounted Mine Detection system uses a standoff sensor to detect mines five to 30 meters ahead.
Researchers at John Hopkins University are developing algorithims to help airborne sensors pinpoint the locations of land mines. Data networking technology can broadcast mine locations to nearby forces, or combine the informations with other data-processing systems.
SHARC DSPs enable Lockheed Martin to achieve -25 dB sensitivity in detection of sea mines
SYRACUSE, N.Y. Designers at Lockheed Martin Ocean Radar & Sensor Systems in Syracuse, N.Y., have developed a hull-mounted sonar capable of detecting underwater mines to a sensitivity of -25 to -30 decibels.
They are achieving this performance by using commercial off-the-shelf (COTS) technologies particularly SHARC digital signal processors (DSPs) from Analog Devices of Norwood, Mass. Originally developed for the British Navy`s hull mine-hunting program, the system is now being marketed internationally.
Increasing sonar sensitivity, which in the past was typically -10 dB and good enough to detect World War II-vintage iron mines, amounts to turning today`s signal-absorbing mines from "marbles into beach balls," says Michael Connery, director of ocean systems business development at the Lockheed Martin operation.
These new mines employ such techniques as composite shells, anechoic coatings, and irregular shapes that have made them what Connery calls "F-117 stealth fighters in the water." To turn them into beach balls, Lockheed Martin engineers have capitalized on several new technologies.
First, the SHARC DSPs increase the processing rate to what Connery identifies as "tens of tens of megahertz" of bandwidth. Engineers also improved the transducers so that they can perform more of the processing at the front end, and send a cleaner signal back to the processors.
Operating frequencies are in excess of 350 KHz, he says. The result is to provide what he calls "almost video images of the target."
One of the techniques employed is pulse compression processing of the return signal to reduce signal reverberation and enhance the signal-to-background noise ratio. The ability to isolate the target from the noise enables mine hunting operators to see well-defined images of the targets in high seas. This includes adverse velocity of sound profiles caused by temperature variations in the water column and other conditions typical of shallow-water regions.
COTS is also used in the 20-inch active-matrix liquid crystal displays, and in the optical-fiber cables used as the data links when the receiver is deployed in the variable depth sonar mode. In the normal hull-mounted mode the operating range is as far as 100 meters in depth. Detaching the sensors on a tether pushes that down to more than 300 meters.
The new sonar system, known as Pathmaker, is for dedicated mine countermeasure vessels, and would accompany deployed naval forces. Based on 10 months of tests with the British Ministry of Defence last year in British waters, the Pathfinder demonstrated a detection radius of about a kilometer around a ship.
During those tests Lockheed Martin`s Ocean operations (the former General Electric oceans operations in Syracuse) competed with Thomson Marconi Sonar in Sophia, France, for the British Hunt program. The program has since been delayed 18 to 24 months because of budgetary considerations but is still an active competition, Connery says.
In the meantime, Lockheed Martin experts are seeking international customers and announced the availability of the system at the Undersea Defence Technology conference in Nice, France, in June.
This is not necessarily a system that fits into the U.S. Navy`s plans. Connery, how-ever, lists the Netherlands, Belgium, and Germany as potential users and says he considers Pathmaker a possibility for upgrades to other mine hunting systems. J.R.
Acoustic sensors used in coastal defense
GAITHERSBURG, Md. Engineers at the Electronic Systems Group of DRS Technologies in Parsippany, N.J., are working on a U.S. Navy project called known as Mobile In-shore Undersea Warfare (MIUW) for defense of coastal areas.
Under two contracts totaling $3.3 million, engineers in the Gaithersburg, Md., facility are developing the primary acoustic surveillance arrays and spare parts for the AN/SQR-17A sonar signal processing system.
MIUW involves mobile vans housing the signal processing equipment and deployed near shorelines for the defense of harbors and coastal regions, as well as for amphibious operation area surveillance.
The acoustic surveillance sensors are deployed on the ocean floor and transit data via optical fiber cables or RF telemetry data links to the AN/TSQ-108A vans on shore. The system provides area surveillance for finding and neutralizing such threats as surface ships, submarines, and swimmer-delivery vehicles. J.R.
Algorithm identifies mines from UAV video images
BALTIMORE Unmanned aerial vehicles (UAVs) are receiving growing attention from U.S. defense officials as a way to find and destroy explosive mines on land and at sea. One way members of the military services use UAVs in this pursuit is to take video images of a beachhead before the arrival of troops.
One big drawback to this, however, is the difficulty that typical UAV sensors have in differentiating mines and harmless rocks and trees from the altitudes where UAVs ordinarily fly.
"First, the mines are relatively small, and second, they`re usually in areas that have a lot of vegetation where it`s difficult to discriminate among shrubs, trees, and mines," observes John Goutsias, a professor of electrical and computer engineering at Johns Hopkins University in Baltimore.
Goutsias heads a team at the Hopkins Whiting School of Engineering whose members developed an algorithm to enable a computer to filter out unwanted material in the surveillance images.
Counter-mine forces today use a six-segment filter that spins in front of the camera lens aboard the UAV. Each segment is a different color, which enables different optical frequencies to pass through. Because there are six filters, the camera produces six different images of the same scene. For example, one filter may cause vegetation to show up more prominently because of the way chlorophyll reflects light.
The algorithm that Goutsias`s team developed enables the computer to use size and shape to help find mines. In this way, the algorithm will disregard trees and other large objects that are unlikely to be mines. Since rocks and vegetation reflect light differently than metal or plastic mines, they show up less often in the images. "If an object of the proper size appears in at least three images, the system decides it is probably a mine," Goutsias says.
The prototype system has detected aboveground mines in an aerial picture in less than a minute and achieved a 95 percent success rate, he adds. Supporting the work are officials of the Office of Naval Research, whose experts used minefield video images from the Coastal Systems Station of the Naval Surface Warfare Center in Panama City, Fla. J.R.
Air Force research aims at counter-mine sensor fusion
UTICA, N.Y. Sensor fusion techniques now in development for the U.S. Air Force may also be applicable to counter-mine activities.
One study aims at integrating data from a variety of airborne sources, such as unmanned aerial vehicles and spacecraft, for integration by such systems as the Joint Surveillance Target Attack Radar System aircraft better known as Joint STARS.
This study is in progress at Integrated Sensors Inc. (ISI) in Utica, N.Y. Company engineers are doing the study for the U.S. Air Force Research Laboratory in Rome, N.Y., under supervision of the Defense Advanced Research Projects Agency.
The two-year study is investigating the use of specialty front-end boards with commercially available embedded computers to process heterogeneous data from moving target indicator and synthetic aperture sources and filter out the false alarms.
The idea is to provide this fused information in real time to battle planners, explains Ed McDermott, president of ISI.
The software is also commercially available. McDermott says he estimates an operational system would cost about $18,000. ISI engineers are focusing on developing the algorithms to provide the best solution. As a measure of the computational complexity, he says a 90-degree sector of an area under surveillance would represent about 240 gigabits of data. J.R.