Night vision technology update: recent international developments in night vision technologies have followed the twin paths of image intensification (12) and thermal. One significant change in recent years, however, has been the convergence of these traditionally separate paths as manufacturers work on a range of developments targeting the tactical `fusion' of both 12 and thermal images. (Technology)(Cover Story).
In the infrared arena, focal plane arrays have replaced the scanned sensors and their complicated scanning mechanism, but a new technology, through Flir Systems and SaabTech, has entered the defence scene; it is known as the Quantum Well Infrared Photodetector.
Recent international developments in 12 technologies have included the development of `thin filmed' micro-channel plate (MCP) image tube technology, filmless tube technology, autogated technology and new 16 mm tube designs that are smaller and lighter than conventional 18 mm and 25 mm tubes.
Along the way, these advances have recently opened a debate concerning so-called `generational' designations of image tubes.
I2 tube technology moved First Generation to Second Generation with the internal change from anode cone to a micro channel plate and from Second Generation to Third Generation with the change from a tri-alkaline cathode to a gallium arsenide cathode. The current debate centres on whether or not the removal of film from the MCP and the addition of a gated power supply justify a Fourth Generation designation by US military representatives.
In a night vision system, an advanced Gen III tube collects ambient light on an objective lens at its input window, passes this light through a photocathode where light photons are converted into electrons, then pass the electrons through a vacuum gap within the tube. After bridging that gap, the electrons pass through an MCP where they are magnified 50 000 to 100 000 times through multiple electron forming collisions on the MCP walls. After filtering through an ion barrier film and second vacuum space, the amplified electrons reach a phosphor screen where they are converted to monochromatic light photons before being collected and presented to the user by the system eyepiece.
The ion barrier film used in Gen III systems is utilised to block stray absorbed gasses dislodged from the surface of the MCPs by electron-to-MCP wall collisions since these gasses became positively charged ions that could damage the photocathode surface and reduce the life of the I2 tube.
Most recently, tube designers have developed the technology to allow removal of the ion barrier, resulting in a filmless tube design. In addition, the unfilmed MCP technology is accompanied by the parallel introduction of automatically gated power supplies that control the on/off speeds of photo-cathode voltage with resulting vision benefits in excessively high light or brightly illuminated environments.
While a debate has recently broken out over specific US generational designation of these latest tubes, US manufacturers ITT Industries and Northrop Grumman's Litton Electro-Optical Systems Division (Leosd) provide representative examples of the latest technology tube designs and systems emerging from manufacturers around the world.
Representative I2 Systems
ITT Industries Night Vision, for example, is offering the latest in thin-filmed Gen III tube technology in its Pinnacle image tubes. Company descriptions highlight the Pinnacle tubes as "featuring significantly higher signal-to-noise ratio (SNR), shock resistance, and end-of-life (EOL) requirements for SNR and gain, as well as dramatically reduced halo. The Pinnacle tube exceeds the performance of all previous Gen III tubes. This major breakthrough in image intensifier technology will benefit aviation and ground forces around the world by providing proven Gen III reliability, yet higher performance than ever-before achieved with this technology."
The Pinnacle performance is being offered in all of ITT's 18 mm Gen III tubes -- MX-10160 (F9800), MX-10130 (F9810) and MX-11769 (F9815) -- as well as in that company's new 16 mm tube designs, which company references describe as "significantly smaller and lighter weight than conventional 18mm tubes. The 16 mm tube -- available in either a filmless Gen IV or filmed Gen III version -- also improves packaging flexibility for night vision system designers." Along with tube advances like Pinnacle, ITT is also offering what it describes as Generation IV `filmless' microchannel plate technology.
Although the now unofficially termed Gen IV technology is not exportable at this time, along with its deliveries under the US Army's current Omnibus V contract award, ITT is offering international customers several systems incorporating its other high performance tube technologies.
One recent system example can be found in ITT's multi-purpose Mini Night Single-Eye Acquisition Sight (Mini N/Seas) monocular. Available with either Gen III or Gen II image intensifier tube technology, the Mini N/Seas monocular can be hand-held, head-mounted, helmet-mounted or weapons-mounted on the M16/M4 family of weapons for use as a night vision scope. Although designed as a monocular, the Mini N/Seas may be easily configured as a dual-eyed binocular (goggles) by attaching two separate monoculars to a helmet or head mount.
ITT Industries' Night Vision system designated Lucie is a new, compact night vision goggle with less forward projection than the typical ground soldier's goggle. Capable of being equipped with high-performance Gen III or state-of the-art Supergen image intensifier tubes, Lucie promises improved comfort and wearability for users while offering a wide (50 degree) field of view. The system operates on one AA battery and can be handheld or head-mounted for hands-free operation.
Northrop Grumman's Litton Electro-Optical Systems Division is also at the forefront of advanced night vision tube and night vision system developments.
For example, the company made its first delivery of `gated filmless tubes' (to use the current politically correct term) in October 1999. At the time, the tubes were described as the result of "intense efforts to expand tube performance levels by taking advantage of new technology developments, and by re-thinking traditional tube design concepts. These investigations allowed [then] Litton to produce image intensifier tubes with no ion barrier film. As seen above, this barrier used in conventional Gen III tubes, prevents damage to the photocathode coating by shielding it from ions backscattered from the microchannel plate (MCP). The unfilmed tube breakthrough is significant enough that PM-NV [US Army Project Manager -- Night Vision] has designated unfilmed tubes, Gen IV. Gen IV tubes used in night vision goggles have demonstrated substantial increases in target detection range and resolution, particularly at extremely low light levels".
Initial application of the Gen IV tube (MX-10130E/UV) was reportedly with the US Special Operations Command's (Ussocom) Improved Night/Day Fire Control & Observation Device (Inod) weapon sight. In addition, the company has been providing advanced Gen III tubes (MX-11620/UV) under its portion of US Army Communications Electronics Command's (Cecom's) Omnibus V contract. System applications under Omnibus V include AN/PVS-7D Infantry Night Vision Goggles, AN/PVS14 Monocular Night Vision Systems and AN/AVS-6 Aviator Night Vision Systems.
In addition to Omnibus deliveries and other domestic and international deliveries, Leosd most recently announced receipt of a new ID/IQ (Indefinite Delivery/Indefinite Quantity) contract from the US Navy's Naval Surface Warfare Center (NSWC) Crane Division to produce 7000 Miniature Night Vision Sights (MNS) for the United States Marine Corps. The initial contract award in fiscal 2001 is for $ 7.9 million. With all quantities produced the total value of the contract is in excess of $ 35 million.
Company representatives note that the MSN was originally selected as the dedicated mini night vision sight (AN/PVS-17) for the Ussocom Sopmod M4A1 carbine programme, adding that "Its light weight, compact design and superior performance has now been matched with US Marine Corps requirements for fielding on their new M4 Carbine program and will also be used on the M16A2 & M16A4 rifles and the M240 and M249 squad automatic weapons. The US Marine Corps miniature night vision sights will also include a submersible capability for up to 20 metres (66 feet) as is standard with several night vision systems supplied by LeoSD to Ussocom."
The MNS is being produced with 2.25 x (5000 ea maximum) fixed infinity magnification to engage targets out to 300 metres. A longer-range version is also being made featuring 4.5x (2000 ea maximum) magnification for ranges out to 500 metres. MNS's capability is 30 per cent greater than the currently fielded AN/PVS-4, which it will replace. Weight is significantly reduced by 47 per cent for the 2.25x and 20 per cent for the 4.5x systems. MNS has been designed with a 30 per cent wider field of view than older systems to enhance target acquisition in close range Mout (Military Operations in Urban Terrain) operations.
Company system descriptions explain that "MNS has gained wide acclaim among user communities for its simple, yet highly effective operation, combining a projected, internally bore-sighted red dot aim point and a unique dual momentary on/off control to save battery power. MNS utilizes the latest advances in image intensifier tube technology, pioneered by LeoSD, including an auto-gated power supply providing Marines with extended dawn and dusk operation in addition to exceptional low light night performance."
While fulfilling current domestic and international orders, US manufacturers are looking toward the next Omnibus night vision procurement by US Army Cecom. June 2001 saw a government announcement that it was considering the issue of a Request for Proposal (RFP) for an Omnibus VI package. The proposed multi-year procurement will cover: the AN/PVS-7D Night Vision Goggles, AN/AVS6(V)IA, AN/AVS-6(V)3 Aviator's Night Vision Imaging System (Anvis), and the AN/PVS-14, Monocular Night Vision Device (MNVD) Systems and associated spare parts, including 18 mm and 25 mm Third Generation Image Intensifier Tubes.
Projections indicate the possibility of RFP release in September 2001, proposals due in October 2001, award approximately January 2002 and first deliveries beginning no later than nine months after award date. Total basic requirements are anticipated to be approximately 8000 each AN/PVS-7 and AN/PVS-14s and approximately 1000 each AN/AVS-6 systems per year.
Industry representatives respond to Wiltsie's statement (see Fourth Generation? Box herewith) by pointing to a presentation by the (then) Army Project Manager for Night Vision on 9 December 1999 that specifically identifies Gen IV as unfilmed/gated systems.
Wiltsie acknowledges that "There are folks in the Army who have talked about Fourth Gen. I'm not going to say that the Army is completely clean on this thing." But Wiltsie also adds that, "There's never been an Army definition that says `Fourth Gen is this and is this.' In fact, over the last six months, we've been debating back and forth over what the definition of Fourth Gen is," he says. "And it comes back to this issue of: When you take the film off, there's going to be an effect on the manufacturing yield which translates into an effect in cost. If that operational improvement isn't significant, why would we do that? And that's the whole issue we're wrestling with now. There are experiments going on as we speak to define this operational improvement."
Wiltsie continued, adding that "Unfilmed has an improvement at overcast starlight which we haven't seen before. Unfilmed also gives you the ability to get your halo down -- the blooming effect around point sources -- around lamp posts and headlights and that kind of thing; which is significant to pilots; which is significant to drivers; which is significant to soldiers who are trying to find people who are hiding behind lights. So that is something that we're calculating into this equation: not only the improvement in range in overcast starlight but also the halo effect. And basically it allows you to move the MCP closer to the cathode and by doing that you can get the halos down."
"So unfilmed is going to give us a much better capability at low light level. No question about it. The question is how much and is it worth the value or the cost to go to unfilmed?" Wiltsie said.
"Now the other thing is the gated side," he continued. "Gating is going to be critical to Military Operations in Urban Terrain; going from high light level -- where the dynamic range is very high -- you go into a room that's completely black -- you kick the door in and the room next to it is lit.
These dismounted soldiers have got to have that capability. The same with pilots, going from very dark areas where they're flying on one side of a mountain -- especially in a place like Korea -- he flies on one side of the mountain -- he's in the shadows of the moon -- it's really, really dark -- he comes around the corner and all of a sudden he's hit with the lights of a city -- gating is critical."
While Fourth Generation debates continue within the I2 community, a number of parallel technology advances are taking place with thermal imaging technologies.
DRS Sensor Systems, for example, is currently in production for the M1A2 Second Generation Thermal Imaging System (Gen II Tis) for the US Army's Horizontal Technology Integration (HTI) program. The Gen II Tis provides M1A2 Abrams tank gunners with an unparalleled all-weather, 24-hour TV-quality extended range detection, recognition, identification and engagement capability.
Company literature notes that, "the Gen II Tis is dramatically superior to the First Generation Thermal Imaging System, extending targeting ranges beyond the weapon limit. The Gen II Tis uses the same Army-developed HTI Second Generation Forward Looking Infrared (Flir) as in the M1 Commander's Independent Thermal Viewer (CITV), the Bradley A3 (Improved Bradley Acquisition System) and the HMMWV (High Mobility Multipurpose Wheeled Vehicle) Scout Long Range Advanced Scout Surveillance System (Lras3)."
The Lras3 example includes a long-range multi-sensor system for the US Army's scout vehicles and provides real-time detection, recognition, identification and pinpointing of distant target locations.
This system provides precise target location by incorporation of advanced Second Generation Forward Looking Infrared (Flir) [HTI Second Generation Flir -- WFOV: 8.0 x 4.5 degrees (16:9), NFOV: 2.6 x 1.5 degrees (16:9)], a global positioning interferometer, an eye-safe laser rangefinder [+/- 5 meters accuracy] and daylight TV sensor [WFOV: 6.0 x 4.5 degrees (4:3), NFOV: 2.0 x 1.5 degrees (4:3)].
Lras3 is designed to bridge the gap between currently fielded and future systems, has entered the production phase with plans to field 630 units to US Army scouts in the current force as well as 51 additional systems to each new Brigade Combat Team. First Unit Equipped (FUE) is projected during 4th quarter FY01.
Thermal, but Qwip
Quantum Well Infrared Photodetector is a term that has recently started to spread in the night vision technology circles. Since the technique was recently introduced into the new Birc night sight for the Bill missile, Armada asked SaabTech Electronics to explain the Qwip principle on which the Swedish firm had been working since the early 1990s as part of a Swedish research project. In fact, the development began at Industrial Microelectronics Centre (IMC) in 1986. The first was produced in 1992, after six years of work, in a project jointly financed by Flir Systems, SaabTech Electronics, Saab Dynamics, FMV and Nutek. The first industrially useable detectors were delivered in 1998. IMC, now called Acreo, produces the detector chip in Kista and delivers it together with the readout circuits to Flir Systems in Danderyd, who integrates it with a cooler.
How does it work? Best is to leave the answer to the above manufacturers themselves: "By, on a suitable substrate, applying very thin layers of different material, a structure of so-called quantum wells can be created. In the quantum well, the energy gap between the valency band and the conduction band is greater than the surrounding material. In this way, the electrons will be caught in the quantum well, roughly like a golf ball falls down in a hole. By selecting the materials correctly, a suitable depth in the well can be created so that a photon of a certain wavelength, which hits the quantum well, can transfer the right amount of energy to the electron so that it is lifted out of the well to the conduction band and an electrical current is created. In this Qwip, the material is alternating gallium arsenide (GaAs) and aluminium gallium arsenide (AIGaAs) and photons in the long wave thermal IR-range can be absorbed.
"Once all layers are placed on a GaAs wafer, parts of the material can be etched away so that a grid pattern is created. By adding a metal contact to every square, a matrix of individual detector elements is created, called pixels. If the electrical signals from every pixel are read, a two dimensional picture of the IR-radiation is created, which is received by the detector. The electrical signals are very small, and in order to be able to separate them from background noise or dark-current effects the detector must be chilled to -203 [degrees] C. This can be done quite easily with a cooler based on the Stirling principle".
The most common detector material used today for the long wavelength IR-range is CdHgTe (CMT), a crystalline material that is difficult to produce in large single-crystal chips -- a prerequisite to obtain a good image quality. Many thermal-cameras have used scanning detectors but these have been replaced by focal plane arrays to get rid of scanning mechanisms, resulting in much improved image uniformity.
Bolometers offer an interesting alternative since they do not require cooling and are cheaper. However their sensitivity is far from meeting the demands of high performance systems.
Raytheon Company Electronic Systems is also continuing both production and development of new technology thermal systems in vehicular and manportable night vision configurations.
In vehicular systems, Raytheon is continuing production of the AN/VAS-5 Driver's Vision Enhancer (DVE). With approximately 1000 DVEs fielded to the US Army to date, the company recently received an additional contract to provide the systems to the US Marine Corps.
Individual and portable crew-served infrared night vision capabilities are found in systems like Raytheon's AN/PAS13B[V]2 Medium Thermal Weapon Sight and AN/PAS13B[V]3 Heavy Thermal Weapon Sight. Both models utilize a high sensitivity mercury cadmium telluride (HgCdTe) focal plane array to detect targets through battlefield obscurants, in adverse weather and in zero illumination situations.
IR + I2
In addition to these systems, one new innovative merging of I2 and thermal imaging technologies can be found in Raytheon's Thermal Integrated Personnel Sight (Tips).
Initially designed by Knight's Armament, the Tips is based on Raytheon's existing standard W1000-15 Uncooled Thermal Weapon Sight with an infrared/ visible waveband beam splitter added to interface with the weapon's existing day scope. One of the most significant tactical features of the Tips is its ability to place the Universal Knight Sight in front of the gunner's scope, with the resulting shooter's image superimposing both thermal and I2 images at a fraction of earlier image combination system options. Undisclosed quantities of the system have reportedly been delivered to selected US Army components.
Other companies like DRS, Thales and Northrop Grumman are also working on infrared and intensified light image fusion. This technique will be covered in a forthcoming issue of Armada International.
RELATED ARTICLE: In short.
* The definition of a 4th generation system is still under discussion -- even though they already exist"
* "The question remains as to whether `filmless' is worth the extra investment"
* "Future systems may incorporate the melding of two or more technologies."
RELATED ARTICLE: Fourth generation?
The pending US Omnibus VI procurement has served to highlight a new generational debate taking place within US manufacturing circles. Specifically, although both ITT and LeoSD are offering Gen IV systems, government representatives have recently started backing away from that designation for filmless/gated systems.
"We never defined' Fourth Gen that way," says Doug Wiltsie, Technical Director for the Army's Night Vision Lab at Ft. Belvoir, Virginia. The issue is this: When the Army designates a `generation' that means that they intend to buy that and that will give them a capability, a proven capability. What the Army is wrestling with right now is whether unfilmed is of significant value. And why I say that is this: when unfilmed came out we thought that the improvement in signal-to-noise was going to be a certain amount. Right now we're trying to quantify what that is. We're trying to quantify how much that is. And that's very important. If, and I'll just make this up, if five meters is the difference in overcast starlight, is it worth the significant amount of money we're going to pay to do that? And that's the real question."
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|Date:||Oct 1, 2001|
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