Development of new night vision devices.
Development of new night vision devices
The overwhelming superiority of any army that has the means to carry out night operations became obvious during the Gulf War in 1990-1991, when the United States and other coalition countries used such equipment intensively. Iraqi troops were helpless against an attacking enemy they could not see.
While the various devices in this area are somewhat competitive, each has its own advantages. Image intensifiers continue to find applications in NVGs and small arms and artillery sights (they can be half the size and weight of other imaging devices), although thermal imagers are slowly beginning to displace them at the high end of the market. This is especially true for armored vehicle sights and portable anti-aircraft and anti-tank systems.
Over the last three decades, image intensifiers have been radically improved, mainly under military pressure to achieve maximum quality at minimum cost. The second-generation (Gen II) devices, which appeared in the early 1970s and are still manufactured by industry worldwide, contain a 2 MCP glass microchannel board, which acts as a toric electron multiplier. It provides a photo signal of 240 μA/lm and allows gain control. The third-generation Gen III image intensifiers, which use a photocathode grown on a substrate and consisting of a separate gallium arsenide crystal bonded to a glass plate, provide photo signals exceeding 1000 μA/lm. A barrier film on the input surface of the microchannel board prevents the backflow of ions (a by-product of image intensifiers) and damage to the sensitive structure of the photocathode. This feature significantly extends the service life of the image intensifier.
Gen III devices entered commercial production in the early 1980s. Since then, the number of suppliers has been reduced to two (ITT and Litton) due to the complex and expensive manufacturing technology required to ensure high quality while competing in a shrinking market and streamlining the industry.
The U.S. Army, which remains the largest purchaser of image intensifiers and related devices, has been purchasing them in batches since 1985. The first three Omnibus programs were divided among suppliers, but in February 1996 Litton Night Vision was selected to fill all the requirements for the Omnibus IV program and awarded a $239 million contract by the Communications and Electronics Directorate of CECOM. Deliveries under this contract include the AN/PVS-7D night vision goggles for infantry, the ANVIS night vision system for aviators, goggles for helicopter and fixed-wing crews, a new AN/PVS-14 night vision monocular, and 95,000 image intensifier tubes.
Both 1TT and Litton Electro-Optical Systems (which also bid for the Omnibus IV contract) have advances in image intensifier tube design, such as new photocathode designs and advanced surface activation techniques, that represent significant improvements over previous third-generation tubes. 1TT's Omnibus IV tube has a minimum photosensor of 1800 μA/lm, with typical values exceeding 2000 μA/lm. By comparison, the Omnibus III PVS-7 tube has a photosensor of 1200 μA/lm, and the Omnibus II tube has a photosensor of 800 μA/lm.
Increasing the photo signal is the key to increasing the signal-to-noise ratio, which is the most important parameter affecting detection limits at low light levels. The Omnibus IV image intensifier used in the PVS-7 has a minimum signal-to-noise ratio of 21, which is 45% higher than that of the Omnibus II version. At the lowest light levels, such as starlight on a cloudy day or under tree canopies in a forest, this results in a 50% increase in detection range (the detection range of a vehicle with 30% contrast in starlight on a cloudy day with the PVS-7 increases from 240 to 360 m). This increase in range was accompanied by a steady decline in price from $6,000 in 1985 to $2,000 in 1997.
Other key parameters for drivers are resolution, which provides the image detail needed to recognize rather than just detect an image, and the frequency transfer function (MTF). 1TT's Omnibus IV image intensifier has a channel board pitch of 6 µm, providing a resolution of 64 line pairs (lp)/mm, compared to 36 lp/mm at best for the Gen III image intensifiers delivered under the Omnibus II program. This, together with the corresponding increase in MTF, will result in an almost 50% increase in detection range in the fourth moon phase. Since the signal-to-noise ratio and photo signal determine performance at very low light levels, and the MTF is more important at higher levels, the comprehensive improvements to the Omnibus IV image intensifier provide a consistent 50% increase in detection range in all ambient conditions.
1TT Night Vision also developed the AN/AVS-8 night vision system under contract to the Air Force Materiel Command Personnel Systems Center. The system is the first U.S.-developed helmet-mounted night vision device designed for ejection. The Air Force plans to purchase 580 production devices.
The purchase will begin in FY99. 1TT previously supplied its F 4949-based night vision devices to pilots of the A-10. This was the first practical use of such equipment on a high-speed jet aircraft in the Air Force.
Litton Electro-Optical Systems continues to develop the Gen III image intensifier tube to ensure that the Army continues to consider the company as a potential alternative supplier and to bid for the upcoming Omnibus V program. The company has also developed a high-resolution Gen II image intensifier tube based on a 6-micron microchannel board, which was included in the Omnibus IV program (where it was included in the Gen III image intensifier tube) to target international markets.
Litton Electro-Optical Systems currently markets products from Insight Technology B. E., Meyers, and Night Vision Equipment Company to overseas customers and plans to add other suppliers to the mix. The company also believes it is the only Western source of a 1.1-µm extended-IR image intensifier tube capable of receiving 1.06-µm Nd:YAG laser light.
The U.S. Army continues to advance new programs that take advantage of advances in image brightness. CECOM is seeking proposals for an improved INOD, a 24-hour fire control and observation device, to be used by special forces on medium and large caliber sniper rifles, as well as for strategic reconnaissance and surveillance. The INOD, which will incorporate a Gen III image intensifier, will allow the sniper to observe both day and night channels simultaneously. The two planned variants, the medium INOD and large INOD, will differ only in the size of the objective lenses.
CECOM plans to award one contract for two phases of development work, to begin in 1997 and be completed in early FY99. Phase one will produce three prototypes of each medium and large INOD, which will undergo development testing and evaluation. Phase two will produce six prototypes of each size for limited user testing. Production of 1,908 systems is planned to begin in FY99 and be completed in FY01. Production may continue into FY02.
The Russian Scientific Production Unit Jeophyzika-NV claims that it can provide Gen III image intensifiers with a photo signal of over 2000 μA/lm and has designed new photocathodes that have an extended spectral response down to 2 μm in the near-IR range. The latter factor allows it to detect reflected radiation from both neodymium-sodium-aluminum-garnet lasers and eye-safe erbitrile-yttrium-aluminum-garnet lasers.
There are many possible technologies that could form the basis of Gen IV image intensifiers, ranging from improvements on existing designs to entirely new concepts. Among those being considered by CECOM are image intensifiers with a new photocathode (which extends the spectral response to 1.6 µm), intensifiers that replace the microchannel board with other intensifier mechanisms, and lightweight multilayer designs with a total thickness of 3 mm. Other prospects include lightweight systems that use common-output image intensifiers and thermal imagers, as well as those that combine near- and mid-IR CCD arrays with miniature flat panels.
The Naval Air Systems Command and the Office of Naval Research and Development are conducting the Color Night Vision System (CNVS) Demonstration Program, which aims to replace the pilot's night vision goggles with a head-operated multispectral imager and helmet-mounted display. Existing designs that directly visualize the output of the image intensifier use a charge-coupled device (CCD) camera to convert the output of the image intensifier into a video signal. The goal of the CNVS program is to eliminate the image intensifier by using CCDs that operate at 1/7th the illumination levels and 2/5th the contrast levels required by earlier designs. Such an imager would have a photoelectric signal of approximately 5400 μA/lm and a quantum efficiency approaching 100% at wavelengths in the 0.55-0.7 μm range.
As part of a complementary demonstration program, the Air Force aims to use panoramic night vision goggles to increase the field of view by 240 percent over existing designs by using new optics advances combined with a compact image intensifier.
Thermal imaging has also seen progress in several areas. Devices with focal plane arrays with a large number of detector elements (both survey and scanning) provide a significant increase in range. In parallel, cameras with uncooled arrays have been developed, which are beginning to take over the market traditionally occupied by devices based on image intensifiers.
Under the Synergi program, launched in 1992 to create a second-generation European thermal imaging system, three companies — Thomson CSF Optronique in France, Zeiss-Eltro Optronic (ZEO) in Germany and Pilkington Optronics in the UK — developed a basic set of modules that they and other manufacturers incorporated into thermal imaging cameras and entire reconnaissance systems. The Synergi program uses a 288 x 4 element receiver developed by SOFRADIR in France. The design of the modules combines low life-cycle costs with small size, low power consumption and high performance.
Thomson-CSF Optronique has incorporated devices developed under the Synergi program into the Catherine, Sylvi and Sophie thermal imaging cameras. The Catherine camera is designed for long-range fire detection and control from armored combat vehicles and for surface-to-air missile launch systems. Poland's PGO has incorporated the camera into its DRAWAT fire control system for the T-72 tank. The Sylvi camera is adapted for use in commander's panoramic sights, such as the one installed on the Leclerc tank from GIAT Industries. The lightweight camera 'Sophie', which was originally intended for infantry, can also be mounted on light armoured vehicles such as the GIAT AMX 10 RC or the Alvis Scorpio.
Thomson-CSF Optronique and Pilkington Optronics have jointly developed the Sabre/Sophie 24/7 sight for gunners and commanders of armoured fighting vehicles. In turn, a British company has developed a camera for sale under the Synergi programme called SGTI (Second Generation Television). ZEO is marketing its similar Synergi 1 camera, which weighs 11.2 kg (including a telescope with a 3×4° field of view), for use in Germany and abroad. The French company SAT is also developing sights based on Synergi for the Trigat anti-tank missile and is using this technology in the piloting system for the Tiger attack and reconnaissance helicopters. Eurocopter company.
In parallel with the Synergi programme, ZEO is working with STN Atlas Elektronik, AEG Infrarot Module (AIM) and Telefunken Mikroelectronik Entwicklungszentrum to develop the Ophelios module suite, based on a 96×4 element receiver. ZEO's camera based on these modules of the same name weighs 8 kg (including a telescope with a field of view of 2.6×3.4° and 8.8×1.8°). The camera can be used in unmanned aerial vehicles, short-range air defence systems, light reconnaissance vehicles, optoelectronic masts on submarines and border protection devices.
The UK's Defence Research Agency (DRA) and British industry have also followed suit. In parallel with the Synergi programme, work is underway to develop infrared systems under the Stairs programme. The Stairs-C modules, demonstrators of which were built by Pilkington Optronics, are based on a 768×10 element mercury-cadmium-tellurium matrix from GEC-Marconi Infra-Red Ltd (GMIL). Pilkington Optronics is currently developing a high-quality infrared camera based on the Stairs-C modules, EPIC, for use in a variety of applications, including the IR detection and tracking system for the Eurofighter.
The US Army has launched the HT1 program to develop a second-generation Forward Looking Infrared (FLIP) system to improve performance over existing equipment while reducing acquisition and operating costs. The program, which is expected to cost $3 billion overall, aims to increase target acquisition and tracking range by 55 percent and the number of targets engaged by 44 percent over first-generation systems based on US Common Modules.
The HT1 program includes a series of scanning systems operating in the 8-12 µm range and using the standard SADA II detector matrix with 480 x 4 elements. In July 1994, a consortium of Texas Instruments and Hughes Aircraft received an order from CECOM for the technical development and production within 48 months of a second-generation forward-looking IR system. In April 1997, these two companies received multi-year contracts worth $98.3 million and $111 million, respectively, for the production of NV-80B kits and their integration into various sights: an independent commander's night vision device and primary thermal imaging sighting system for the gunners of the M1A2 Abrams main attack tanks and the Bradley independent commander's night vision device and improved target acquisition and tracking system of the Bradley M2A3 tanks. The second generation forward looking IR systems can also be used on the AH-64 Apache attack helicopter, the RAH-66 Comanche reconnaissance helicopter and the prospective LRAS 3 long range reconnaissance system.
Uncooled thermal imagers offer several advantages over cooled ones, but do not have the disadvantages associated with mechanical scanning, cryogenic cooling, enclosure in vacuum Dewars or high-pressure vessels. Flat arrays of uncooled imagers are used in applications that require low mass, low power consumption, minimal maintenance and fast turn-on. According to calculations by the American company Amber, the transition from cooled to uncooled systems reduces the cost of an imager from $50,000 to $20,000. The receivers include ferroelectric (also known as pyroelectric) arrays made of materials such as barium-strontium-titanium and lead-scandium-tantalum, and sensitive resistance thermometers known as microbolometers.
The DRA in Malveru, UK, supported the development of uncooled arrays in 100×100 element formats. In 1993, it awarded a contract to GEC-Marconi Sensors to produce demonstrator models of the STAIRS A, based on a pyroelectric array developed by GEC-Marconi Materials Technology, suitable for use in gun sights and lightweight reconnaissance devices. The two companies are also working with European partners, including Signaal USFA and Delft Sensor Systems, which has developed the LION lightweight infrared surveillance sight to meet requests from 767 units of the Royal Netherlands Army. They are also marketing their devices internationally in collaboration with UK partners and Thomson-CSF Optronique of France. Production was expected to begin in 1977.
LION is based on a lead-scandium-tantalum detector matrix with 256×128 elements operating in the 8-13 µm range, and is usually equipped with an optical system with a three-fold increase, providing a field of view of 10×5°. According to available information, this allows the detection of a vehicle at a distance of 2 km, recognition at a distance of 700 m, and identification at a distance of 350 m, with the image appearing on a binocular display made on a CRT. The sight weighs 2 kg, has dimensions of 10x20x24 cm and a power consumption of 7 W. It can operate for about 10 hours on six lithium batteries or about 2 hours on standard alkaline batteries. The absence of a refrigerator leads to the sight being ready for operation almost instantly (the time to enter the mode is less than 5 s). The noise from the sight in operation is reportedly inaudible from a distance of 2 m. GEC-Marconi Sensors is currently developing a 384×288 element matrix for medium and long range.
In the United States, the Defense Advanced Research Projects Agency (DARPA) issued a series of contracts for the development of prototypes of the SRTS short-range thermal sight and the LOCUSP low-cost uncooled night vision device under the programs of the same names. They were followed by the SMRT-II program for the development of an improved medium-range thermal imaging sight, under which Texas Instruments supplied devices to the Night Vision and Electronics Directorate. This sight can be equipped with rifles, machine guns, and Stinger surface-to-air missile launch tubes, or used as a hand-held night vision device. Texas Instruments claims that this improved version is the most compact, lightweight, inexpensive, and energy-efficient of all available long-wave thermal imaging sights. It weighs less than 1.6 kg, consumes only 3.5 W of power (up to 4.5 W at extreme temperatures), can operate continuously for more than 15 hours on a BA6874U battery, and does not require a scanner or cryogenic refrigerator. The uncooled 245×325-element matrix, which operates at a steady temperature of 21 ° C, provides a good-quality image in just 20 seconds after power is applied.
Texas Instruments used similar devices in the AN/VAS-5 driver vision enhancer, which the Army plans to install on armored fighting vehicles and trucks. The company is also scheduled to deliver 12 prototypes of a new reconnaissance aid and gun sight by June 1998 under a $5.7 million contract. The ISM integrated sighting module technical demonstration by the Night Vision and Electronics Directorate, part of CECOM, is part of the Force XXI Land Warrior program.
The objective is to demonstrate the integration of an eye-safe laser rangefinder, thermal imager, electronic compass, eye-safe laser designator, and direct-view optics into a weapon sight that is lightweight, rugged, and low power. Under this contract, Texas Instruments will manufacture nine short-range variants of the sight for individual weapons and three long-range variants for group weapons. The ISM sight can also be used for reconnaissance and target acquisition.
The large potential market for commercial uncooled thermal imaging systems has led to the formation of consortiums to develop specific systems in this area. DARPA is funding three of them under the Dual-Use Technology Exploitation Program and the previous Industrial Reinvestment Program. One goal is to achieve a unit cost of less than $10,000 in mass production.
Lockheed Martin IR Imaging Systems leads a consortium working to reduce the cost of monolithic microbolometer instruments. Other members of the consortium include Ageme Infrared Systems, Heneywell Military Avionics, and MIT Lincoln Laboratory. Lockheed Martin's LTC 500 camera, based on the SIM 100 modular imager, which contains a 327-by-245-element matrix, weighs 2.35 kg (including a 40° lens). The ULTRA consortium, led by Inframetrics, is targeting products based on the monolithic microbolometer developed by Heneywell's Technical Center. Other ULTRA members include the U.S. Navy's Surfare Warfare Center and Boeing North American's Autonetics fe Missile Systems Division. The latter division of Boeing currently supplies its uncooled U3000 arrays (mounted in the focal plane) in the 320×240 format. Texas Instruments and its partners are developing barium-strontium-titanium ferroelectric structures such as SMRT II.