Optical warfare: technology emerges to see the enemy, and to blind him
Visible-light and infrared sensors are crucial tools for battlefield commanders concerned with surveillance and fire control, but optics can also be a lethal way to destroy these sensors and render expensive weapon systems - and soldiers - sightless.
By John Haystead
Optical sensors and tracking systems - ranging from the most sophisticated infrared focal plane arrays to simple visible-light telescopic sights - are critical elements of waging modern warfare during the day and at night; that was clear during the Persian Gulf War. Few of today`s tactical weapons, in fact, can function at all without optical sensors.
Given this total dependency, it would seem that military systems designers would be foolhardy not to develop some form of countermeasures to these ever- proliferating optical devices. For the same token, perhaps it also would behoove policymakers in the U.S. Department of Defense to begin formulating official optical warfare doctrine.
Nevertheless, the most straightforward and effective optical countermeasures technology at best is at a crossroads, and at worst may be mired in the same political debate that revolves around land mines. It seems that optical countermeasures approaches are entangled in the worldwide distaste for their potential application as antipersonnel weapons.
Much like another highly efficient optical sensor - the human eye - electronic optical sensors are extremely vulnerable to damage or destruction from directed laser energy. It is precisely because of this relationship that the development and deployment of anti-sensor laser systems is so controversial. Because international law bans the military use of antipersonnel lasers, in fact, the development of anti-sensor laser systems has also been slowed or re-directed.
Many existing low-energy lasers that act as target designators and rangefinders, however, already pose a threat to electro-optical sensors. These devices are certainly capable of destroying or disrupting optical sensors or magnifying optics of many weapon- systems, although they are not generally powerful enough in themselves to be considered weapons. Laser designators and thermal imaging systems, once detected, can be quickly countered with return fire from directed laser weapons.
Similarly, lasers can detect and destroy the image-intensifier systems of night-vision equipment. Low-light television guidance systems are particularly susceptible to laser disruption. Lower-energy continuous-wave or high pulse-repetition-frequency lasers can be effective in temporarily disabling optical sensors or in cracking or permanently distorting the glass lenses of optical imaging systems - also called "crazing" - at very long ranges.
"There`s no doubt that research and development of low-energy laser weapons is progressing rapidly to fulfill the urgent need to counter the many different optical sensors on the modern battlefield," says Dr. Myron Wolbarsht, professor of opthomology and biomedical engineering at Duke University in Durham, N.C., and co-author of a recent book on the subject of laser weaponry*.
Although treaties now exist prohibiting the use of lasers as antipersonnel weapons, there is no such restriction on their development as electronic countermeasures, Wolbarsht notes. "It is safe to assume that low-energy laser systems are under development as antisensor weapons," he says.
Prior to the 1995 anti-personnel laser treaty, several laser countermeasure systems were in rapid development by the U.S. military and others. Whether their primary targets were originally to be sensors, personnel, or both is not known, yet those that continue in some fashion today are defined strictly as electronic countermeasures systems.
Most anti-sensor laser weapons are too large for soldiers to carry, and must enter the battlefield on combat vehicles.
Stingray, a system developed for the U.S. Army Bradley fighting vehicle, was originally intended to detect, track, and neutralize fire-control systems on enemy ground vehicles and aircraft beyond their effective firing range. A design of Lockheed Martin Electronics & Missiles in Orlando, Fla., Stingray successfully completed advanced technology development and is now being integrated into training units with the Task Force 21 Advanced Warfighting Experiment at Fort Hood, Texas.
It will probably also be involved in the National Training Center exercises scheduled for March at Fort Irwin, Calif., explains Chris Keller, past acting program manager in the U.S. Army Communications Electronics Command (CECOM) Systems Engineering Division at Fort Monmouth, N.J.
As per direction from officials of the U.S. Army Training and Doctrine Command at Fort Monroe, Va., however, the Stingray systems are only being used in their optics-detection mode, and not as countermeasure systems. Stingray, along with all such programs is closely monitored by DOD for compliance to strict laser protocols that presumably prohibit their use in an offensive mode, Keller says, adding that "Stingray continues to be in complete compliance with all protocols."
Stingray is is an active laser interrogator that locates and identifies high-threat targets that "would be difficult to find using other means," Keller says. The Stingray uses a solid-state, diode-pumped laser.
A tactical and training version of the system has been developed. The training version operates in the near-IR band while the tactical system is a higher-power device operating in multiple regions, Keller says. Other sources have suggested the system is a Nd:YAG, short-pulse, high-peak-power laser operating in the near-IR spectrum.
Originally, six additional evaluation systems were scheduled to be delivered to the Army in 1994 with a follow-on production of 48 systems planned, but there is currently no funding identified for the system. "The future of the program is uncertain right now, although we`ve had good feedback from the units using the systems," Keller says.
A man-portable, rifle-mounted system with similar capabilities to Stingray is the Laser Countermeasures System (LCMS), managed by CECOM`s PM-Night Vision at Fort Belvoir, Va. Mounted on an M-16 rifle, LCMS is intended to disrupt the fire-control optics of ground systems and aircraft.
The public stigma of laser weapons, however, led to its demise, says John Gresham, the Army`s deputy project manager for reconnaissance, surveillance and target acquisition, (RSTA) at Fort Belvoir. "LCMS was never intended as an antipersonnel weapon," he says. "Because it uses a day/night capable laser, it came under scrutiny by anti-laser-weapons groups and was cancelled."
Some funding was retained to continue development of the system`s target-detection mode capability through a new program known as the Target Location Observation System (TLOS).
TLOS combines third-generation image intensifier technology with a low-powered, near-IR laser illuminator that searches for reflections from enemy optical systems. A specially-designed power supply gates the laser on and off at a high repetition rate generating very short bursts of energy, but which provides light-levels sufficient for the image intensifier tube to detect threats in daylight and nighttime operations.
Under contract to Sanders, a Lockheed Martin company in Nashua, N.H., an initial delivery of four TLOS systems is scheduled for June. Eventually the $16.8M program calls for production of 249 systems over the next year and a half.
TLOS can be either handheld or mounted on an M-16 rifle and has an eye-safe hazard range of 25 meters, says Kevin Hunt, TLOS Project Leader, PM NV/RSTA. The system is being evaluated for light-infantry as part of Task Force 21 exercises at Fort Irwin. "So far, the feedback is very positive, as soldiers begin to understand the benefits of active acquisition of optical systems," Hunt says. The specifics of deployment are still being determined but TLOS will probably be initially provided to personnel at Fort Bragg, N.C., and at Fort Campbell, Ky. Hunt says their are no plans for implentation of an integrated laser-based countermeasure capability, however.
The "Coronet Prince" advanced optical-sensor countermeasure pod was originally intended to detect and incapacitate the guidance systems of air-defense weapons. Managed out of the Electronic Warfare Division of the U.S. Air Force Wright Laboratory Avionics Directorate at Wright-Patterson Air Force Base, Ohio, the pulsed-laser system was developed by Westinghouse, now Northrop/Grumman in Baltimore, and underwent final flight-testing in 1989.
"We were able to demonstrate the performance requirements set out for the program," says Dr. Duane Warner, program manager, EO Warfare. "At that time due to budget cuts, we were unable to get funding for additional testing." The test program was therefore concluded and a final report was published in 1990.
Warner says eye-safety protocols never influenced Coronet Prince and that "optical countermeasures are still very much an activity being pursued by the Air Force." Although the Coronet Prince pod is now in a museum at Northop/Grumman, the program`s results and technology have been passed on to follow-on classified programs and research activities, Warner says.
The 1995 "Vienna Protocol," adopted by the Vienna Review Conference of the 1980 United Nations Convention on Certain Conventional Weapons, strictly prohibits the use and transfer of laser weapons specifically designed to cause permanent blindness. It also requires national leaders to take all feasible precautions, including the training of their armed forces, to avoid permanent blinding through the legitimate use of other laser systems. This is the first time that both the use and the transfer of a weapon has been entirely prohibited under international humanitarian law.
While rightfully hailed as a major humanitarian accomplishment, a treatied prohibition does not entirely eliminate the possibililty of their use in conflict. For example, although not optimized to the task, and of questionable tactical value, many anti-sensor laser systems are capable of, or are easily converted to, use as antipersonnel weapons.
"Present laser devices are deemed likely to be used against eyes and sensors whatever benefit they can yield," Wolbarsht says. According to studies by the International Red Cross, if lasers were used intentionally to inflict blindness, so that blinding as a method of warfare became common practice, serious eye damage might account for between 25 and 50 percent of all casualties.
There is strong evidence that antipersonnel laser weapons may have already seen limited use in combat. For example, the Laser Dazzle Sight developed by the British Royal Signal and Radar Establishment in Malvern, England, was designed to blind aircraft pilots, and was reportedly in use on British navy ships for several years and may have led to the loss of three Argentinian aircraft in the 1982 Falklands War.
A blue-light laser, it would have had a range of from 1 to 3 miles. And, although there is no documentary evidence, it is believed that Vietnamese military forces used Soviet carbon dioxide lasers in combat to blind Chinese soldiers in the 1970s, the Soviet military used lasers in Afghanistan, and that Iraqi forces used them in their war with Iran.
Even laser systems having nothing to do with antipersonnel or anti-sensor applications, such as rangefinders and guidance systems, are potentially injurious to the eye.
"We`re really not talking about anti-sensor technology so much as lasers operating at certain wavelengths such as visible and near-IR," Wolbarsht says. The most common laser is the Nd:YAG, which is also one of the most dangerous to the eye and, in its primary wavelength of 1,064 nanometers, is almost invisible. Although Nd-YAG beams are visible at their frequency-doubled wavelength of 532 nanometers, these pulsed lasers are equally or more hazardous because they don`t allow time for any evasive action.
Several low-energy lasers are intrinsically capable of inflicting permanent eye damage when operating in the 400 nanometers to 1,400 nanometers "retinal hazard" region. These include the erbium YAG laser at 1540 nanometers, frequency- doubled ND:YAG 530 nanometers, ruby 690 nanometers, Nd:YAG 1,060 nanometers lasers, argon 488/514 nanometers, titanium-sapphire 660/980 nanometers, alexandrite laser 700/815 nanometers, and tunable free-electron lasers. There are many documented cases of accidental eye injury, military and civilian, from laser devices. Nominal Ocular Hazard Distances have been established for laser rangefinders and designators.
High-energy systems can cause permanent corneal injury, retinal burns, and ocular bleeding outside the retinal hazard region, but their practical use as anti-personnel weapons is questionable. For example, medium-powered carbon dioxide lasers operating at 10,600 nanometers and chemical deuterium fluoride at 3,800 nanometers are capable of doing damage, but 1 joule per square centimeter of energy would have to hit the eye before it closes. This would require a laser powered at 10 watts per square centimeter.
Anti-personnel lasers focus the laser beam on the retina, relying on the eye`s natural magnification of light by some 100,000 times. Thus, a low-energy laser which would have no effect on other body tissue could conceivably destroy the central retina - leaving the victim permanently blind. Wolbarsht says he believes, however, that most eye injuries from low-energy lasers are unlikely to result in total blindness. Nevertheless, lasers can easily destroy the portion of the eye`s visual field used for detail work such as reading signs or aiming a rifle, which would cause significant and potentially permanent incapacitation - especially for soldiers on the battlefield.
Temporary or "flash" blindness is sometimes discussed as a humane use of antipersonnel lasers, but in reality the energy level required for flash blinding is so close to the threshold for permanent blinding that it can only be achieved consistently under ideal conditions in which distance, angle of exposure, atmospheric pollution, and other factors are precisely controlled, Wolbarsht says. "Even then flash blinding could occur only at night when the eye is most sensitive to low levels of light. In daylight, the amount of light energy required to attempt flash blinding would almost inevitably cause permanent blindness instead," Wolbarsht says.
*Some of the quotes directly attributed to Dr. Wolbarsht in this article are extracted with the author`s permission from the text, "Laser Weapons - The Dawn of a New Military Age," co-authored by Maj. Gen. Bengt Anderberg of the Swedish Army. (Plenum Publishing Co. New York, copyright 1992.)
A new program known as the Target Location Observation System, which can be either handled or mounted on an M-16 rifle, searches for reflections from enemy optical systems.
The Coronet Prince advanced optical-sensor countermeasure pod was designed to detect and incapacitate the guidance systems of air-defense weapons. The pulsed-laser system underwent final flight-testing in 1989.
Stingray for the Bradley fighting vehicle was designed to detect, track, and neutralize fire-control systems on enemy ground vehicles and aircraft beyond their effective firing ranges. It is an active laser interrogator that locates and identifies high-threat targets.
The man-portable, rifle mounted system with capabilities similar to Stingray is the Laser Countermeasures System, which was mounted on an M-16 rifle to disrupt the fire-control optics of ground systems and aircraft. The public stigma of laser weapons led to its demise.
To date most research in antipersonnel laser protection has been directed at protecting personnel using optical sensors in high-tech environments such as aircraft pilots, tank commanders, command and control officers, etc.
However, this is the wrong emphasis, given that antipersonnel lasers, implemented as infantry-level weapons, can instead generate widespread casualties, says Dr. Myron Wolbarsht, professor of opthomology and biomedical engineering at Duke University in Durham, N.C.
"The problem needs to be considered from a mass-casualty perspective and this is not being properly addressed. It`s not only a medical-response question, but also one of troop morale when you consider the psychological effects of mass-blindness on the morale of fellow soldiers," Wolbarsht says.
According to Red Cross studies, surgical treatment of laser injuries is sometimes possible in cases where the laser has caused hemorrhages in peripheral areas of the retina. Even then the outcome is uncertain, however, and highly trained doctors are obliged to operate within 48 hours in advanced medical facilities. Such facilities are rare even in industrialized countries, let alone near battlefields.
Today, protection against the effects of anti-personnel lasers is virtually impossible without also severely hindering the wearer`s visibility. Also, although protective goggles can filter out lasers of known wavelengths, many modern lasers can be tuned to multiple wavelengths or designed to fire at many wavelengths simultaneously.
Despite international treaties, Wolbarsht says he doesn`t believe there is any question that there are anti-personnel laser weapons being developed somewhere. "It`s too easy to modify existing systems to the application." - J.H.
Distances at which some typical lasers pose a threat to human eyes
Distance in miles
Naked eye 8x optics 13x optics
Tank rangefinder, ruby 10 23 80
Tank rangefinder, Nd:YAG 4 16 22
Portable rangefinder, Nd:YAG 1 6 9
Portable target designator, Nd:YAG 8 25 3
Airborne target designator, Nd:YAG 25 46 80
These ranges refer to nominal ocular hazard distance