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Sensors Bolster Army Prowess

By Clarence A. Robinson Jr.

 

The Terrain Commander from Textron Corporation provides the basis for the U.S. Army's unattended ground sensor (UGS) Future Combat Systems. The sensor assembly is equipped with a variety of optical, acoustic and seismic devices. Note the laptop computer for displays in a sensor cell.

Combat forces aided by new devices find tanks and mines, thwart ambushes.

Flush from recent combat success in Iraq and Afghanistan, U.S. Army officials are touting a new generation of sensors to help gain battlefield advantages while protecting soldiers from a wide range of threats. Robotic and unmanned sensors are being used to avoid placing soldiers—already operating under hazardous battlefield conditions—directly in harm’s way, especially inside darkened enemy caves and tunnels.

The Army considers the use of sensors and unmanned systems significant to its transformation capabilities and Future Combat Systems (FCS). This approach is so important that a rapid equipping unit that reports directly to the Army’s vice chief of staff is fielding robots, remote unattended sensors and related datalink technologies.

Part of this new process also involves rapid but prudent applications of robots and ground-based unmanned weapons systems, according to Edward T. Bair. He is the Army’s program executive officer for intelligence, electronic warfare and sensors (PEO IEW&S), Fort Monmouth, New Jersey. Robotic platforms equipped with electro-optic and infrared cameras are being used to enter and explore al Qaida underground chambers in Afghanistan.

“We soon had robots searching cave hideouts along the Afghanistan-Pakistan border,” Bair says. “In Iraq, emplacement of remote battlefield sensors helped protect U.S. forces, using seismic, acoustic and imaging devices.”

A small, tripod-mounted AN/PPS-5 ground surveillance radar (SIGNAL, May 2003, page 23) is another sensor that helps detect and identify movement of hostile forces in Iraq out to a range of 20 kilometers. Deployment of this radar “played an important role during combat against snipers and other nontraditional attacks,” he adds.

Bair notes that unattended ground sensor (UGS) technologies continue to transition from the Defense Advanced Research Projects Agency (DARPA) to the Army. The effectiveness of these sensors is directly proportional to the capability of command, control and communications links as well as deployment method, he adds. The use of unmanned ground vehicles (UGVs) or robots to place the UGS systems in front of or just behind enemy positions is one option.

Another alternative is to use unmanned aerial vehicles (UAVs), especially vertical landing and takeoff platforms, such as ducted-fan organic air vehicles (OAVs), an offshoot of DARPA’s micro air vehicles (MAVs). Mounting sensor suites on OAVs offers the potential advantage of flying into an area 50 to 75 kilometers away, listening and observing for specified periods, and rapidly relocating to other areas of interest.

There are still some technical hurdles in the near term for UGS systems, Bair maintains. Nevertheless, the military intelligence advantages to be gained by deploying and operating remote and unattended sensors far outweigh drawbacks. In earlier test scenarios, Bair continues, remote sensors demonstrated the capability of detecting and simultaneously tracking three targets. In more recent tests, the sensor suites are able to detect and track up to 10 targets simultaneously using from six to eight sensors integral to each UGS payload.

These robotic sensors remain in a dormant state to conserve energy until triggered by enemy activity. The UGS systems also can be moved from position to position as battlefield dynamics dictate. As this technology flows to the Army, it is being handled by the program manager for robotic and unmanned sensors (PM RUS), part of the PEO IEW&S.

DARPA is restructuring its MAV program schedule, which could affect OAV availability. The OAV is a slightly larger version of DARPA’s micro air vehicle for use at battalion level and below. The OAV is designed to accompany Army FCS robotic ground vehicles. The micro air vehicle program is focused on a small system suitable for backpack deployment and single-man operation, whereas the OAV is a larger system transported aboard one of the FCS ground vehicles.

An agreement with Honeywell calls for the company to develop and demonstrate the OAV concept. Robotic Technology Incorporated is developing the OAV under the FCS contract. This scalable-in-size UAV is for launch and control from a high mobility multipurpose wheeled vehicle or a robotic platform. The OAV is designed for reconnaissance, surveillance and target acquisition. The MAV and therefore OAV push the envelope in small, lightweight propulsion, sensing and communications technologies. Following a military assessment in 2004, approximately 25 MAVs are scheduled for transfer to the Army in 2005.

Other vertical takeoff and landing tactical UAVs, such as the Northrop Grumman Fire Scout, could be used to deploy UGS systems. Bair explains that other delivery methods also are being pursued, including a cannon-launch capability that could fire the sensors to areas where they self-deploy. “The Army earlier demonstrated the technical feasibility of firing expendable electronic warfare jammers and signals intelligence payloads from artillery tubes,” he points out.

Current Army UAVs cannot remain continuously on station for 20 to 30 hours for surveillance and reconnaissance. UGS systems are a very attractive alternative, particularly because they leverage the commercial cellular telephone industry’s power supply management technology, Bair reports. “The remote sensors go into a sleep mode until triggered to automatically activate and capture the information on what is taking place around them, process it and send it back to command and control cells.” In some instances, the information can be transmitted to overhead UAVs for subsequent relay to other UAVs before reaching a groundstation.

Sensor technology development by the Army’s Communications-Electronics Research and Engineering Center, Night Vision and Electronics Directorate, Fort Belvoir, Virginia, applies across the board to UAVs, UGVs and UGS systems, Fred C. Petito explains. He is director of the air and netted sensors division. Research and development work involves advanced electro-optic (EO) and infrared (IR) payloads, airborne video surveillance, hyperspectral sensors, image processing and overall support for a variety of unmanned and robotic platforms, he adds.

Image processing work supports the Army’s unmanned combat rotorcraft, and work in hyperspectral and other sensors is for larger UAVs. But even the Army’s larger UAVs are small in comparison to those of the other services. Most sensor advances, however, also are for use with the Army’s smaller UAVs. While these payloads are small and lightweight, they must be nearly as capable as those used on larger airborne platforms, Petito offers. In addition to sensor size and weight, cost also is a constraint.

Affordability coupled with size and weight drives performance tradeoffs in development programs, Petito continues. Technology for small platforms encompasses uncooled infrared, charge coupled device airborne video surveillance, acoustic, chemical and passive countermine sensors. One key example he cites is an inexpensive sensor gimbal that is based on commercial technology. It enables an advanced EO/IR payload to work on tactical UAVs.

“We have built a lot of functions into this payload, which contains multiple sensors. The package provides analog and digital capability with 640 x 480 pixels on an indium antimonide wafer operating in the mid-infrared wavelength, with three fields of view—search, intermediate and very high resolution,” Petito says. The payload weighs approximately 55 pounds and also features a color television camera, a laser range finder and a laser target designator, which is being added.

A passive minefield detector in the advanced sensor exploits spectral characteristics of disturbed earth by using a filter. This payload, originally designed for the Shadow 200 UAV, Petito reveals, is now being developed for use with the Fire Scout UAV helicopter for the FCS and may be used on the Hunter UAV. The Hunter already is being equipped with new payloads, including antitank munitions, and will be retained in the inventory for the foreseeable future.

One major advantage of the advanced EO-IR payload, which allows twice the distance or twice the resolution, is a high-fidelity strip-mode mosaic display capability for images captured through a repeated step-and-stare activity, Petito relates. “This system uses a magnetic inner gimbal and a backscan mirror that enables scanning very large areas of 300 square kilometers with high resolution. Imagery is downlinked to a groundstation where it is stitched together in a mosaic, forming a big picture. The technology involved is based on DARPA and Sarnoff Corporation developments.”

The advanced EO/IR payload with its digital imagery also is equipped with aided target recognition, fast wide area search, near-real-time step-and-stare mosaic display and precision target registration capabilities. The IR imagery automatically steps for use in mosaic displays. After a single pass by a UAV, imagery can be overlaid on reference images digitally stored at the groundstation. Using DARPA’s airborne video surveillance technology, the imagery goes to a Sarnoff processor at the groundstation that automatically lines up and geographically locates target positions on a map within 10-meter accuracy. The underpinning for this technology is digital terrain elevation data (DTED) provided by the National Geospatial-Intelligence Agency. These overlays and DTED techniques, Petito claims, help reduce target errors. Thermal, step-and-stare wide area scans, geographically registered to satellite reference data, are already being accomplished in real time.

An example of aided target recognition involves a manned-unmanned scenario that links Army attack helicopters and UAVs flying ingress and egress routes to provide targeting information. The critical capabilities are wide area search, multiple target acquisition, real-time location updates and laser target designation.

Aided target recognition (ATR) technology in the advanced EO/IR payload “chips” out specific images and displays them on the map whenever it spots possible targets. These high-resolution “chips,” Petito discloses, are displayed electronically in real time at the bottom of a map. The capability has been successfully demonstrated in Army exercises.

Limited datalink bandwidth can restrict image fidelity, he explains. “Putting aided target recognition capability in the airborne platform and using one or two circuit cards provide 14-bit, 30-hertz data flowing into the ATR, which enables transmission of only high-resolution chip images to groundstations. Wide area mosaic imagery is sent at slower data rates since nothing changes very quickly,” Petito says. “This enables cropping out a small picture within a picture, which translates to lower data rate requirements, resulting in high-fidelity images. The ATR capability is critical, especially in linking UAVs to attack helicopters or to unmanned vehicles on the ground.”

Emerging hyperspectral sensors on UAVs show promise in detecting and locating camouflaged and concealed mobile tactical vehicles, Petito claims. The sensor technology breaks up red, green and blue into approximately 300 bands, exploiting spectral rather than spatial content in images. However, this also requires a different type of ATR, to feed from 140 to 300 bands into a real-time processor looking for spectral anomalies—colors that do not belong in an image.

The hyperspectral sensor key is algorithm-based signal processing for reasonable detection without triggering too many false alarms. Each sensor pixel comprises a unique, contiguous spectrum for identification of surface materials. By averaging colors in one location with those in surrounding locations, as an example, camouflaged objects can be detected. “They do not match the background across all the bands, and that’s where we get you,” Petito stresses.

In recent warfighting exercises hyperspectral sensors detected a camouflaged air defense site adjacent to a landing zone. Earlier, when more conventional sensors were used, the area was reported to be clear. Work is continuing on an electronically programmable spectral sensor with template matching capabilities.

The Compact Airborne Spectral Sensor is another Night Vision and Electronic Sensors Directorate laboratory program. Objectives are to develop a visible near infrared (VINIR), short wavelength infrared (SWIR) and hyperspectral sensor package for broad area coverage, Petito says. The VINIR/SWIR device senses energy in 400 to 700 nanometers, and at 700 nanometers to less than 1.5 microns, it operates in the near infrared wavelength. This daylight sensor is being used to locate hard-to-find targets and for surface mine detection, Petito clarifies.

Another laboratory hyperspectral longwave imager for the tactical environment program provides a 24-hour reconnaissance, surveillance and target acquisition capability. And, a spectral detection algorithm development program called hyperspectral airborne multimission exploitation and reconnaissance is used with testbed aircraft to perform data collections and analyses. This program is structured to enable rapid movement of forces through and around minefields and hidden enemy positions.

The night vision laboratory is at the forefront of developing technologies for use on small UAVs. Petito continues that 0.25-pound uncooled infrared sensors have been developed that have fewer mechanisms that can fail. These sensors use energy detection physics to locate targets at a range of about 1 kilometer, adequate for small UAVs. They have been adapted from rifle sights and cost approximately $10,000 each. One infrared sensor, which weighs 0.7 pounds, operates with 640 x 480 pixels.

As part of its sensor development effort, the laboratory uses a variety of UAV platforms as testbed aircraft. He adds that acoustic sensors also are being developed as “a poor man’s foliage penetration system on small UAVs,” where the weight of radar is prohibitive. When imaging or hyperspectral sensors detect what are believed to be tanks hidden in tree lines, as an example, a UAV employs acoustic sensors to verify the target and help avoid armor ambushes. Tank engines continuously idle, producing noise.

The night vision laboratory is emphasizing weight, size and power miniaturization in sensors that operate with high resolution and reliability throughout the spectrum. These sensors exploit various phenomena to pinpoint enemy forces, whether hidden or camouflaged. Affordable, high-performance, multimission sensor payloads are critical to the Army’s future force concepts—manned or robotic, airborne or ground-based. Indeed, maturing sensor developments are key components in meeting rapidly changing battlefield scenarios with versatility and precision strike capabilities.