Shine on, deadly light.

Mounted on manned or unmanned aircraft, or operated by front-line ground forces, the laser designator has revolutionised the art of attacking ground targets but, as this article explains, more refinement is needed.

The four armed Iraqi insurgents were probably confident that they had lost their pursuers. Realising that US troops were approaching their location one night in January 2005, they had fled from the building and into the darkness of the night. As they crouched in the weeds along the Euphrates River, the US soldiers walked straight past them.

A conventional operation to flush them out would have taken a whole battalion of men, a tactic that might not have been practical for an army with only a limited number of 'boots on the ground'. Luckily, there was a 'high-tech' solution.

The insurgents might have eluded the soldiers, but they were still being observed by a US Air Force F-16 Fighting Falcon flying thousands of feet above their position. The fighter aircraft turned on its laser designator, 'painting' the Iraqis with infrared light they were invisible to them but visible in the soldiers' night-vision goggles. Their position exposed, the men were promptly arrested.

Laser designators are normally used to illuminate targets being attacked with semi-active laser-guided missiles, bombs or artillery rounds. For an attack to be successful there must be a direct and unobstructed line of sight between the designator and the target. The presence of trees, leaves, grass or other vegetation may prevent the use of a ground-based laser designator, or create a laser spot short of the target upon which a semi-active laser-guided weapon could home, perhaps endangering the designator. Jungle conditions can even limit the effectiveness of airborne laser designators.

Clouds attenuate laser energy and degrade the ability of such guided weapons to see the 'spot' of reflected laser energy in the target. Since the laser spot can only be acquired after the weapon comes out of the cloud, the time available for target acquisition is short. For the attack to be successful, the cloud-base must not be too low, and the weapon must be delivered to a location close enough to the target to ensure precise acquisition and homing.

The designator and the weapon must be set to the same pulse code, the delivery system must place the weapon into the required footprint or envelope and the designator must 'lase' at the correct time and for the required duration.

Although laser energy transmission is unaffected by darkness, the same cannot be said for the operator of the designator. Round-the-clock combat requires that the designator be fitted with a night sight.

Battlefield obscurants such as smoke and dust may attenuate or reflect the laser beam. This can reduce the energy reflected from the target to the point where the weapon cannot lock-on, or might even home onto a false target. A traditional 'rule of thumb' is that if the observer can see a target through either day or night optics he can successfully designate it.

Uh-oh!

If the angle between the sightline from the designator to the target and the flight path of the weapon from its launch point to the target exceeds about sixty degrees, the weapon's seeker may pick up relatively little of the reflected laser energy. Should the designator come into the field of view of the seeker, the latter may detect the energy scattered from the beam as the latter leaves the seeker's optics and 'see' the designator as the strongest source of laser energy.

Reflection, refraction and specular diffraction may be the phenomena that lie behind desert mirages and the summer heat-haze in the middle distance on a road, but they can also create havoc for laser designation. Several years ago, laser-guided bombs released by B-52s taking part in a firepower demonstration in Qatar landed on a line of parked US Marine CH-53 helicopters, destroying two and killing a US Marine. An investigation concluded that specular diffraction might have diverted the laser designator beam, directing the bombs to the wrong location.

Laser designators are offered by a wide range of companies. When India sent out a request for proposals for a ground-based designator it solicited information from at least 16 companies. This article can only look at a handful of systems to illustrate the range currently available.

A Few Examples

The Cilas DHY 307 laser target designator, used by the French services and various export customers, was designed for special forces as a stand-alone device, but it can also be mounted on an optronic turret. It consists of an illuminator box carrying the x7 magnification sighting and 1.064-micron laser system, a control box, a power supply and a tripod whose angulation head can supply target elevation and azimuth. Designed to be compatible with all laser-guided weapons conforming to the Nato Stanag No 3733 standard, it can be programmed to handle Russian or other patterns of pulse code.

For British forward air controllers Thales developed the LF28A LTD, a lightweight, man-portable laser rangefinder and target designator that has been exported to users including the Royal Netherlands Army. Based on an all solid-state slab geometry laser that does not require cooling, it weighs less than 6.6 kg, and has a maximum range of ten km. It is designed to have a short activation time, a feature that reduces power consumption (laser-designators are notoriously power-hungry). An integral x10 telescope is used for aiming, but an interface is provided for an add-on night sight.

The Northrop Grumman AN/Ped-1 Lightweight Laser Designator Range-finder entered initial service with the US Marine Corps and was selected by the US Army in 2004. It incorporates an eye-safe laser rangefinder, a 3 to 5-jam focal plane array thermal imager, a CCD day camera, embedded GPS receiver, digital magnetic compass and inclinometer and a laser designator. It was designed to meet the demands of the digital battlefield. This class of functionality may be impressive but results in a system that weights 16 kg.

For aircraft applications a laser designator needs to be fully stabilised in at least two axes of rotation. The result is usually an underwing pod, or a 'ball' mounted beneath the aircraft. In practice, the designator is normally teamed with one or more electro-optical imaging channels (often with wide and narrow fields of view) and an automatic tracking system.

One of the most successful recent designs has been the Rafael Litening, which is featured in the title picture of this article. In addition to being in Israeli service, this has now been selected by Brazil (F-5E/F), Chile (F-16), Germany (Tornado IDS), Greece (F-4E), India (Mirage 2000), Romania (MiG-21 Lancer), Sweden (JAS 39 Gripen), Spain (F/A-18) and Venezuela (F-16) and several unidentified customers (F-5E, Jaguar, MiG-27 and Su-27/-30). It is also in US service as the AN/AAQ-28(V). Known platforms are the F-15E, F-16C/D, AV-8B Harrier, A-10A, and B-52H. Current production version is the AN/AAQ-28(V)4 Litening AT.

The Litening pod combines CCD cameras, a staring flir, a laser designator, a laser marker, a laser spot tracker and an inertial navigation sensor. The laser designator uses a different optical aperture to the imaging sensors. This arrangement ensures that laser energy is not reflected back into the imaging sensors.

Raytheon's AN/ASQ-228 Advanced Targeting Flir (Atflir) combines the functions of three existing systems--the AN/AAS-38A/B Nite Hawk targeting flir, the AN/AAR-50 navigation flir and the AN/ASQ-173 laser designator tracker/strike camera. It weighs 191 kg, about 150 kg less than the three systems it replaced, and is no larger than the AN/AAS-38A/B. The pod combines a staring MWIR focal-plane array targeting flir, a CCD camera, and a high-power diode-pumped laser. These share a common optical path, while a navigation flir is installed in the adapter that connects the pod to the aircraft.

The US Air Force now regularly releases ordnance from altitudes of 20,000 ft or more in order to remain above the lethal zone of manpads and light anti-aircraft artillery. The designator in the Atflir has been demonstrated at up to 50,000 ft.

There is a growing user demand for designators incorporating a dual-frequency laser able to operate at eye-safe wavelengths for training missions, and be switched to the 1.06-[micro]m frequency for combat use.

Elop's dual wavelength Switchable Eye-safe Laser Range-finder Designator (Selrd) was developed to replace the existing single wavelength designator mounted in the Boeing/McDonnell (now DRS) mast-mounted sight of the OH-58D Kiowa Warrior helicopter. The designator enables the pilot to switch back and forth between the designation mode and eye-safe 1.57-[micro]m (training mission) frequency Based on technology developed for the cancelled RAH-66 Comanche helicopter, the device will also be retrofitted in modified form to the Tads turret of the AH-64A and AH-64D Apache.

Most US Air Force Predators used during the 1999 operation Allied Force over Kosovo carried the L-3 Wescam Model 14TS sensor, a 14-inch sphere containing an infrared camera and two daylight colour cameras. Frustrated by the problems involved in getting a designator-equipped aircraft to locate and illuminate a target being observed by a Predator, the service embarked on a fast-paced programme to remove one of the Predator's daylight cameras and replace it with a laser designator. This upgrade was developed in only two weeks.

From late 2001 onwards, all new-build Predators were fitted with the Raytheon AN/AAS-52 Multispectral Targeting System, which has a third-generation IR sensor, wide-angle TV camera and a laser designator.

Another crash modification programme took only three months to take the next logical step--arming the Predator with underwing-mounted Hellfires so that it could locate, designate and destroy time-sensitive targets.

If AH-64 Apaches can position themselves where they can't be heard or seen, and a laser-designator-equipped drone is in the area, the helicopters can 'pop up' and engage the designated targets with their Hellfires.

Multiple Targeting

On current designators the laser is mechanically boresighted to the centre of the designator's field-of-view. Since a target being attacked with a semi-active laser-guided missile or munition must be illuminated throughout the final stages of the flight of the weapon to the target, the operator cannot realign the designator or a fresh target until the first weapon has scored. Even if multiple targets are present in the field-of-view, they must be dealt with one at a time. This may leave the operator of the designator or the vehicle, aircraft or UAV on which the designator is mounted exposed to possible counterattack.

Research has been under way for more than a decade on ways of creating designators able to illuminate multiple targets. Recent advances in laser technology have produced solid-state, beam-steerable lasers. If used in a designator, these remove the need for the laser to be bore-sighted to the sensor field of view.

For example, a patent awarded to the Electronics & Space Corporation of St Louis, Missouri, describes how a laser beam could be steered to any location within the field of view by means of acousto-optic deflectors or diffraction gratings. Multiple objects within the field of view could be designated as a target, and thereafter simultaneously tracked and illuminated with laser radiation, each target being allocated a separate coded signal. A salvo of missiles, each converging on its individual target, could rapidly destroy all the targets, minimising the exposure time of the designator and its operator or platform.

Electron Guzzlers

One problem that won't go away in the near future is that of providing a lightweight source of power. A lecturer's laser pointer may be content to run off a pair of AAA cells, but it is not required to project its beam for up to ten km. Laser-designation hardware may be shrinking in size, but its power demands are not. That may not be a problem in an aircraft-mounted system, but in tactical front-line ground positions it translates into lots of spare batteries.