How other low-light imaging technologies compare to image in

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How other low-light imaging technologies compare to image in

Postby cj7hawk » Thu Feb 26, 2015 6:41 pm

For over a century, we've known how to make cathode ray tubes, and very little has changed from the same fundamental technology that was developed in a time when computers weren't even imagined. Yet the digital world developed and we ended up with two ways to do things – and while image tubes are yet still analogue, or at least, function as analogues, image processing mixed with digital sensors have created an entirely new family of equipment.

Yet despite digital technology replacing analogue technology in almost every area, image intensifier tubes have held on to the #1 night vision technology position since their inception. This article looks at some of the existing technologies, the up and coming technologies and how they might impact on our use of image tubes and our perception of night vision technology.

Much of it may seems like science fiction, but to be fair, so did night vision when it was first developed. I've included links to the current state of development for each of the less common technologies.

Also, over the past few series of questions and related articles, I've posted extensive details on the weaknesses and strengths of image intensifier tubes, so if you have a moment, please visit this thread ( http://nightvisionforums.com/viewtopic.php?f=1&t=7272 ) and help me with the final three questions of the series – This research is providing information to one of the largest NV manufacturers in the world, and will help to influence future image intensifier development.

Thermal

Thermal's hardly new and while early versions were fundamentally analogue in nature, formed of scanning lines and mirrors and displays they used persistence of vision to create an image. Thermal imaging now covers both the LWIR and MWIR spectral ranges, and developments such as the TCAD ( Thermal Collimated Aiming Device ) allow for the equivalent of laser aiming while using thermal, specifically against human targets.

Thermal exists as a standalone product, or as an enhancement to other imaging technologies such as "Thermal Fusion” where an intensifier image is overlaid with a thermal image or thermal outline, with devices like the COTI allowing post-fitment to COTS image-intensifier based night vision systems.

However most thermal imaging development over the past decade seems to have occurred in two distinct areas – the pitch and composition of the focal plane array ( the sensor ) which includes advances in materials – extending to materials that can operate in both MWIR and LWIR regions of the spectrum, and the other area is the algorythms that process the information.

As a result, thermal NV devices are constantly getting smaller, cheaper and provide a better image than those even a decade ago – while image intensifier technology and performance hasn't really changed much at all over the same period.

Additionally, thermals are now being included even into cellular phone based systems and other integrated solutions are now making them far more available than they have been at any other time.

At the pointy end of development, the frame rate is increasing, along with resolution and the sensitivity of the FPAs has improved to detect smaller variations in temperature. The result of this is that modern images are starting to look more like photoshopped conventional images, showing fine details where previously they tended to display similar temperatures as a single shade, resulting in images that showed people or animals as single coloured silhouettes.

Although thermal imaging is already accepted as an alternative to image intensification, and also exists with it as "fused” technology where it is combined with image intensification, it's biggest weakness still seems to be power consumption, with modern digital screens and processors contributing significantly to the problem.

This is not the only area in which thermal devices have not yet reached similar levels of quality that Image Intensifier based systems have enjoyed for over two decades. A common issue with all thermal monoculars is that most thermal manufacturers seem to have a weird idea of what "unity” magnification is, with +/- 50% seeming to fit into the bracket as well, and even better models often being out by up to 20%.

Still, Thermal technology is probably the only other serious solution to many low-light and especially no-light imaging requirements at the man-portable level at this time.

Digital

Digital image intensification isn't all that new – but it's been limited in the past by low levels of sensitivity, which makes it difficult to image well under low-light levels, especially those approaching NL6.

SWIR and Out of band NIR development has recently been extending, and it is starting to appear that digital NV will extend through the full SWIR range up to around 1.7 microns.
http://www.militaryaerospace.com/articl ... riefs.html

Like thermal, Digital systems similarly include a focal plane array or sensor that can detect and image light outside of the visible range, and then displays this on a small screen, although unlike thermal, most digital based technology doesn't require as much image processing and so the power requirements for most digital systems is still caused by the screen. Additional to this, current micro-sized screen resolutions available typically will not exceed XVGA or 1024x768, which in turn limits the practical size and resolution of the sensor itself.

Digital systems nonetheless exist widely, but only over the past decade as it achieved the sensitivity needed to make it a practical alternative to image intensifier tubes. Unfortunately, this level of digital technology is still not widely available to the public yet, leaving most existing digital systems performing at the same level as first-generation night vision equipment.

The exception to this rule is SWIR-only based systems, for which cameras are presently already available, however the cost of these units is presently keeping many from civilian marketplaces outside of security applications.

Digital systems that operate in the SWIR spectrum also have the advantage that many airborne particulants that obscure atmospheric visible-spectrum light are small enough that light around 1500-1700nm is not significantly scattered, making SWIR very useful for seeing through smoke and other atmospheric obscurants.

Cost and power use still remain the biggest hurdles for this technology to overcome if it is going to seriously challenge image intensifiers as the main technology used in military and civilian night vision.

Pulsed-laser gated and Time Multiplexed imaging

Image

Pulsed-laser gated imaging isn't new – and it's something that can be incorporated into an IIT based system, as it was the development of image intensifiers that led to pulsed-laser gated imaging in the first place. Most commonly available through Russian manufacturers, it's an active-laser-based system that uses the fast-gating to only the show light reflections from a certain distance. Because of this, it addresses back-scatter related issues that make it difficult to see through some obscurants, like water and smoke.

These systems can also be used, when combined with image processing, to create 3D models of the environment around them, making them very similar to LIDAR in application.

Pulsed-laser gated systems typically involve the source of the laser and the imager being a part of the same device, however they can also include external sources, allowing for such uses as being able to utilise night vision within a well-lit areas. Normally, artificial lighting near night vision equipment impacts the effectiveness of the technology.

However, by time-division-multiplexing an image intensifier with any light illuminating an area, they can be dimensionally separated in time so that the light does not interfere with the image intensifier operation, allowing full-distance viewing by night vision devices, and effectively making local lighting disappear from the image.

Virtual Imaging

( Augmented Reality / False Reality / Mixed Reality / Superimposed Virtual Reality )
Imaging systems: http://www.pnnl.gov/news/release.aspx?id=1033

Image

Virtual imaging isn't an imaging technology per-se, but more a reflection that we don't need real images to operate in an environment – An example would be a virtual image of an environment, in which physical images are replaced by generated images, not based on photonic or radio imaging, but on the knowledge that they are there, and of their characteristics – eg, size, shape, color, position etc. An example might be that a detection system identifies the sound of a common piece of hardware, eg, a personnel carrier, and using various methods, knows what it is, where it is, roughly what direction it is headed and so builds a virtual model of the item, and overlays it on the current image – Such technology potentially allows targets and threats to be identified through or behind obstacles, and can be as simple as an icon, or as complicated as a full model.

Image

An example of a virtual image comprised of real-time LIDAR data (buildings) and virtual data (the tank) based on other known information. Immediately, it's clear that some pats of this recreated environment, such as windows, would not normally be visible to the observer given his location.

Virtual imaging also includes displaying items that simply can't be detected easily, but that are well known, eg, hidden sensors around an objective based on radio detection, well-known patrol routes, vehicles expected to be hidden, personnel areas within a building, walls within a building, etc.

These aspects of a virtual image cannot be seen or detected normally, but if their position is known, then by holding a 3D physical model of the surrounding area and knowing both the position and orientation of the person using the device, it's possible to display them with absolute accuracy through a virtual imaging system.

Virtual imaging also includes medical use, and may one day be of immense value to civilian shooters, identifying safe directions in which a shot can be taken, or could even show other party members obscured from view by including telemetry data and location information.

Virtual imaging is most commonly found today in augmented reality solutions, which overlay the information over real imaging, but can also be used in the absence of real imaging if the model is sufficiently detailed and accurate. This technology is still only infancy, and there are connections between augmented reality and virtual imaging, they are not the same – Augmented reality can include virtual imaging, but virtual imaging can also be standalone. Virtual imaging is critical to techniques such as ghost and reflective imaging, as neither technique produces a real image, but instead produces a representation of what exists within a certain space.

Technologies for getting the image to the eyes can include VR headsets, optical waveguides and direct retinal imaging.

LIDAR

https://www.youtube.com/watch?v=8nTFjVm9sTQ
(A music video made from LIDAR Virtual Imaging)

Image

LIDAR is somewhat the photonic version of radar, and allow complicated imaging with depth information included. To this extent, it can provide direct imaging or virtual imaging of an object.

LIDAR is also a fully active technology, in that it must supply the source of the light that it uses to create an image, and as such, it has limited use for military applications, but is used extensively where covertness is not a requirement. The technology provides significant benefits with respect to the fine detail that can be detected, and this can be displayed with enough contrast so that the detail is not missed by the viewer. To this extent, LIRAD is exceptional at imaging up the wires of overhead power lines, which can be quite difficult to pick out visually even during the day. It can also pick out objects quite difficult to see due to the speed of the object, such as propellers and helicopter rotors.

Militarily LIDAR can be useful for identifying objects at a distance, especially within a very narrow FOV, where it takes full advantage of the active technology.



Quantum Ghost Imaging
http://www.fastcompany.com/3009438/tech ... st-imaging
or
http://skullsinthestars.com/2009/10/31/ ... t-imaging/
and
http://defensesystems.com/articles/2014 ... aging.aspx

Image

A recently developed virtual imaging technology, this uses quantum entanglement to view something that cannot be viewed by direct imaging models. It is similar to LIDAR, except that it can be used to see objects that are placed in such a way that any photons that strike the object are either absorbed ( stealth materials ) redirected or reflected in a different direction and cannot be redetected.

It does this by entangling photons, then firing one photon at a detector and the other at a sensor. Rather than receiving reflected photons or information from the target, the entangled photon is measured to determine if something has happened to the imaging photon, and from this, a virtual image is built up.

Because of this, ghost imaging is an effective technology for detecting stealth objects, or seeing through obscurants. Although at the very edge of science fiction – being able to detect something that cannot be seen at all

This technology has already been demonstrated under laboratory conditions, but is not yet known to work in the field.



Reflective imaging

( Image Processing of reflected light )
https://www.youtube.com/watch?v=JWDocXPy-iQ
2012 at MIT

Reflective imaging is an imaging technology that allows objects to be seen around a corner by converting normal objects into mirror-like objects – It can work passively or actively and slowly builds up a model of hidden or obscured detail based on mathematical processing of analysing reflected light – Such a technology is quite useful as it provides the capability to see objects that are hidden behind walls or obscured by physical objects, yet for which a path for light can exist. To this extent, current technology works well enough to potentially identify whether a threat exists within a room when the open door to the room can be seen and used for imaging purposes.

It has been already been confirmed possible in the laboratory, using a normal door as the reflector to look into a room. Although the door diffuses light, it is also illuminated by different levels of light that is reflected off of objects within the target area, and through image processing of the different light levels, an original image can be built up. Active scanning technologies increase the accuracy and reliability of these systems.

Audio Imaging

Example: http://phys.org/news/2013-05-world-hand ... ready.html
or
High Resolution: http://www.sorama.eu/content/sorama-int ... sorama-cam

Audio virtual imaging is another highly effective technology, similar to sonar, but using sound maps to build up images – In it's simplest form, it can detect the location of sounds. In a more complex sound-pressure focal plane array, it can provide an image of the sound, locating specific tones even in a noisy environment.


Image

Sometimes known as sound cameras, these devices are available in the field and have the capability to pick out individual rifle shots during a battle, amidst mechanical and chemical noise, with pinpoint accuracy – They also have the capability to locate difficult to find noise sources, and are great for finding the source of unusual sounds in an engine, when other noises are already present and making it difficult to track down the location of the specific noise that is being sought out.

Current audio arrays are of fairly limited resolution, but could be built into helmets ( size of the array is quite important at present ) and be overlaid as a form of virtual imaging or augmented reality.

Although sound imaging is a passive technology, it could be enhanced with sonar to provide a virtual image of the surroundings of a sensor which would then be relayed to the user's eyes. This level of technology is still presently not available, but is likely to exist within the next ten years. Passive systems can also use ambient sound pressure waves to build an image, and unless the objects being viewed are silent and there is no background noise, such a system does not require any active components.

Because audio imaging can be combined with virtual imaging eliminating the requirement for real-time image modification, it is possible to build up a 3D virtual world through virtual imagine that reflects, accurately, objects that are difficult to pick up in real time through audio imaging alone.

UWB Imaging

( Ultra-wide-band radar, through-wall radar, iradar, impulse-radar ).
https://ipo.llnl.gov/technologies/indiv ... ulse-radar

Also known as "heartbeat detectors”, these are already considered a military staple in just about every call-of-duty game, but their existence in reality is a little different. These systems are often handheld, but they are quite large so often must be held in both hands. Although this means they are currently larger than would be suited for everyone to carry, within a virtual imaging environment, only a single person would need to use one to allow everyone in their squad to see what was going on on the far side of the wall.

Simple versions can detect motion, while large man-sized ( and portable ) arrays can detect images suitable for identifying people or threats – including landmine detection and location of conduits and cables underground to a depth of several metres.

Although an active technology and while current systems are quite large, as imaging software improves this may eventually reach the point that it can be head-mounted, allowing site of targets through walls at ranges out to about 50 yards. UWB is also well suited to detecting the flight path of small projectiles and may one day for a warning system to let the user know if they are being targetted, though in a world of measures and countermeasures, using such an active system may leave the user as a target in any event.

SQUIDs (MRI)

Super-conducting Quantum Interference Devices are the most sensitive magnetic detection systems known to man.

For a long time I wasn't sure that these were actually being used for much outside of industrial and medical application, but when they suddenly appeared as an add-on to ITAR it was clear that they were being used in military development as well. Most civilian work with SQUID based MRI technology seems based around airport threat detection and to this extent it's pretty advanced already, however given that these things can detect the magnetic fields within the human body at a range of over 100 meters, and are expected to be able to do MRI scans using only the earth's magnetic fields in the future, they could provide the basis for future detection systems.

Image Intensifiers.

Although this article isn't about image intensifiers, it is about how they compare to modern and future technologies.

Presently, one of the most significant benefits of image intensifiers is that they use extremely low levels of power to produce a functional image of the environment – working at very high efficiency, they produce light images using about the same level of light that a single LED might produce.

In the past, 40 hours were expected of most image tubes, but with technological advancement, modern tubes are currently pushing towards 80 hours of continuous use with a single AA battery, making them immensely suited to the battlefield where they do not require constant resupply or recharge. They also have negligible heating, and so are not easy to detect by thermal means.

Additional to this, actual power usage is sufficiently low that solar recharging is practical, meaning that a single NOD might well power itself through sunlight collected during the day, even with a very small charging panel, though the long life of very small batteries seems to have precluded sych developments.

The size of modern image intensifiers is still extremely small compared to other technologies, and the main contributor to the size are optical components, including the image inverter. The effective accuracy of IITSs and optical configuration that more simply supports unity magnification, coupled with larger screen makes it very practical to use cheap components and overall the cost effectiveness of image intensifiers is still close to optimal for what they produce.

Thermal seems to be coming a close second – especially with heavy consumerisation of the technology, as they need no light at all and are equivalent in operation both day and night, even if they do suffer from a lack of thermal contrast twice a day.

Imagers like the COTI do well with power, but still only provide about 3 hours of use from a battery that would provide up to 100 hours of use with an image intensifier, and even then the COTI benefits from the fact an image intensifier is still needed to amplify the image to visible levels.

This in and of itself marks the single biggest difference between image intensifiers and other equipment – Only in image intensifier based equipment do you get people returning kit as faulty when the only fault is "Battery is flat”.

The second major differentiator is resolution. Image intensifiers still provide more image detail than a HD TV, which thermal and digital systems are still struggling to catch up to. It's not an apples-for-apples comparison, because image intensifiers still suffer MTF related resolution loss more than digital devices, but generally, the image from a modern tube is sharp and detailed.

Price is the third factor – as both digital and thermal manufacturing costs are dropping in price and the manufacturing techniques and scale of production are likely to result in further drops as much of the technology is dual-use.

A fourth factor is image naturalness. Image intensifiers, while providing an image that is only slightly skewed into the near-infrared, still provide an image that is instantly recognisable when compared to daylight images, without needing further processing.

Digital systems can do similarly, but even now, recent image intensifiers are increasing contrast levels and matching what can be achieved digitally even at the edge of development.

And there seems still more developments to come. Color imaging is possible and while current systems are bulky, there's no reason that future manufacturing technologies won't make color images standard, even at high resolutions.

Overall, while the future of night vision is starting to look very advanced, with features that far exceed current technologies, image intensifiers still reign king at the current time and will likely do so for the next decade - even as they are enhanced by other technologies.

Questions about image intensifiers

Over in this post ( http://nightvisionforums.com/viewtopic.php?f=1&t=7272 ) there's some questions about Image Intensifiers and IIT based NV gear. Your input is appreciated and will help provide feedback that will influence tube developments over the next decade.
cj7hawk
 
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