Infrared vision

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Infrared vision is the capability of biological or artificial systems to detect infrared radiation. The terms thermal vision and thermal imaging, [1] [2] are also commonly used in this context since infrared emissions from a body are directly related to their temperature: hotter objects emit more energy in the infrared spectrum than colder ones.

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The human body, as well as many moving or static objects of military or civil interest, are normally warmer than the surrounding environment. Since hotter objects emit more infrared energy than colder ones, it is relatively easy to identify them with an infrared detector, day or night. Hence, the term night vision is also used (sometimes misused) in the place of "infrared vision", since one of the original purposes in developing this kind of systems was to locate enemy targets at night. [3] However, night vision concerns the ability to see in the dark although not necessarily in the infrared spectrum. In fact, night vision equipment can be manufactured using one of two technologies: [4] light intensifiers or infrared vision. The former technology uses a photocathode to convert light (in the visible or near infrared portions of the electromagnetic spectrum) to electrons, amplify the signal and transform it back to photons. Infrared vision on the other hand, uses an infrared detector working at mid or long wavelengths (invisible to the human eye) to capture the heat emitted by an object.

The infrared spectrum

The infrared bands in the electromagnetic spectrum. Infrared spectrum.gif
The infrared bands in the electromagnetic spectrum.

The entire electromagnetic spectrum highlighting the infrared part located between the visible and the radio waves, is depicted in the figure. The IR spectrum can be subdivided into 5 regions, although this definition is somewhat arbitrary and it differs from one author to another. [5] [6] [7] [8] The subdivision presented here is based on a combination of the atmospheric transmittance windows, i.e. the wavelengths regions in which infrared radiation is better transmitted through the atmosphere, the detector materials used to build the infrared sensors and the main applications. In this way, the Near Infrared (NIR) band is mostly used in fiber optic telecommunication systems since silica (SiO2) provides a low attenuation losses medium for the infrared, whilst the Short Wave Infrared (SWIR) band allows to work on long-distance telecommunications (remote sensing) using a combination of detector materials. The Medium Wavelength Infrared (MWIR) and the Long Wavelength Infrared (LWIR) bands find applications in Infrared Thermography for military or civil applications, e.g. target signature identification, surveillance, NonDestructive Evaluation, etc. The Very Long Wavelength Infrared (VLWIR) band is used in spectroscopy and astronomy.

Infrared spectral bands. IR detectors table.gif
Infrared spectral bands.

The MWIR band is preferred when inspecting high temperature objects and the LWIR band when working with near room temperature objects. Other important criteria for band selection are: [9] the operating distance, indoor-outdoor operation, temperature and emissivity of the bodies of interest. For instance, long wavelengths (LWIR) are preferred for outdoor operation since they are less affected by radiation from the Sun. LWIR cameras are typically uncooled systems using Focal Plane Array microbolometers commonly used in industrial IR applications, although cooled LWIR cameras using Mercury Cadmium Tellurium (MCT) detectors exists as well. On the contrary, the majority of the MWIR cameras require cooling, using either liquid nitrogen or a Stirling cycle cooler. [10] Cooling to approximately −196 °C (77 K) offers excellent thermal resolution, but might restrict the span of applications to controlled environments.

Applications

Infrared vision is used extensively by the military for night vision, navigation, surveillance and targeting. For years, it developed slowly due to the high cost of the equipment and the low quality of available images. Since the development of the first commercial infrared cameras in the second half of the 1960s, however, the availability of new generations of infrared cameras coupled with growing computer power is providing exciting new civilian (and military) applications, to name only a few: [11] buildings and infrastructure, [12] works of art, [13] aerospace components [14] and processes, maintenance, [15] defect detection and characterization, law enforcement, surveillance and public services, medical and veterinary thermal imaging. The electronic technique that uses infrared vision to "see" thermal energy, to monitor temperatures and thermal patterns is called infrared thermography.

On February 14, 2013 researchers developed a neural implant that gives rats the ability to sense infrared light which for the first time provides living creatures with new abilities, instead of simply replacing or augmenting existing abilities. [16]

See also

Related Research Articles

<span class="mw-page-title-main">Infrared</span> Form of electromagnetic radiation

Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around 1 millimeter (300 GHz) to the nominal red edge of the visible spectrum, around 700 nanometers (430 THz). Longer IR wavelengths are sometimes included as part of the terahertz radiation range. Almost all black-body radiation from objects near room temperature is at infrared wavelengths. As a form of electromagnetic radiation, IR propagates energy and momentum, exerts radiation pressure, and has properties corresponding to both those of a wave and of a particle, the photon.

<span class="mw-page-title-main">Forward-looking infrared</span> Type of thermographic camera

Forward-looking infrared (FLIR) cameras, typically used on military and civilian aircraft, use a thermographic camera that senses infrared radiation.

<span class="mw-page-title-main">Night vision</span> Ability to see in low light conditions

Night vision is the ability to see in low-light conditions, either naturally with scotopic vision or through a night-vision device. Night vision requires both sufficient spectral range and sufficient intensity range. Humans have poor night vision compared to many animals such as cats, in part because the human eye lacks a tapetum lucidum, tissue behind the retina that reflects light back through the retina thus increasing the light available to the photoreceptors.

<span class="mw-page-title-main">Thermographic camera</span> Imaging device using infrared radiation

A thermographic camera is a device that creates an image using infrared (IR) radiation, similar to a normal camera that forms an image using visible light. Instead of the 400–700 nanometre (nm) range of the visible light camera, infrared cameras are sensitive to wavelengths from about 1,000 nm to about 14,000 nm (14 μm). The practice of capturing and analyzing the data they provide is called thermography.

<span class="mw-page-title-main">Thermography</span> Use of thermograms to study heat distribution in structures or regions

Infrared thermography (IRT), thermal video and/or thermal imaging, is a process where a thermal camera captures and creates an image of an object by using infrared radiation emitted from the object in a process, which are examples of infrared imaging science. Thermographic cameras usually detect radiation in the long-infrared range of the electromagnetic spectrum and produce images of that radiation, called thermograms. Since infrared radiation is emitted by all objects with a temperature above absolute zero according to the black body radiation law, thermography makes it possible to see one's environment with or without visible illumination. The amount of radiation emitted by an object increases with temperature; therefore, thermography allows one to see variations in temperature. When viewed through a thermal imaging camera, warm objects stand out well against cooler backgrounds; humans and other warm-blooded animals become easily visible against the environment, day or night. As a result, thermography is particularly useful to the military and other users of surveillance cameras.

<span class="mw-page-title-main">Transparent ceramics</span> Ceramic materials that are optically transparent

Many ceramic materials, both glassy and crystalline, have found use as optically transparent materials in various forms from bulk solid-state components to high surface area forms such as thin films, coatings, and fibers. Such devices have found widespread use for various applications in the electro-optical field including: optical fibers for guided lightwave transmission, optical switches, laser amplifiers and lenses, hosts for solid-state lasers and optical window materials for gas lasers, and infrared (IR) heat seeking devices for missile guidance systems and IR night vision.

<span class="mw-page-title-main">False color</span> Methods of visualizing information by translating to colors

False color refers to a group of color rendering methods used to display images in color which were recorded in the visible or non-visible parts of the electromagnetic spectrum. A false-color image is an image that depicts an object in colors that differ from those a photograph would show. In this image, colors have been assigned to three different wavelengths that our eyes cannot normally see.

<span class="mw-page-title-main">Far infrared</span> Light with 15-1000 μm wavelength

Far infrared (FIR) is a region in the infrared spectrum of electromagnetic radiation. Far infrared is often defined as any radiation with a wavelength of 15 micrometers (μm) to 1 mm, which places far infrared radiation within the CIE IR-B and IR-C bands. The long-wave side of the FIR spectrum overlaps with so named terahertz radiation. Different sources use different boundaries for the far infrared; for example, astronomers sometimes define far infrared as wavelengths between 25 μm and 350 μm.

<span class="mw-page-title-main">Multispectral imaging</span> Capturing image data across multiple electromagnetic spectrum ranges

Multispectral imaging captures image data within specific wavelength ranges across the electromagnetic spectrum. The wavelengths may be separated by filters or detected with the use of instruments that are sensitive to particular wavelengths, including light from frequencies beyond the visible light range, i.e. infrared and ultra-violet. It can allow extraction of additional information the human eye fails to capture with its visible receptors for red, green and blue. It was originally developed for military target identification and reconnaissance. Early space-based imaging platforms incorporated multispectral imaging technology to map details of the Earth related to coastal boundaries, vegetation, and landforms. Multispectral imaging has also found use in document and painting analysis.

<span class="mw-page-title-main">Mercury cadmium telluride</span>

Hg1−xCdxTe or mercury cadmium telluride is a chemical compound of cadmium telluride (CdTe) and mercury telluride (HgTe) with a tunable bandgap spanning the shortwave infrared to the very long wave infrared regions. The amount of cadmium (Cd) in the alloy can be chosen so as to tune the optical absorption of the material to the desired infrared wavelength. CdTe is a semiconductor with a bandgap of approximately 1.5 electronvolts (eV) at room temperature. HgTe is a semimetal, which means that its bandgap energy is zero. Mixing these two substances allows one to obtain any bandgap between 0 and 1.5 eV.

A staring array, also known as staring-plane array or focal-plane array (FPA), is an image sensor consisting of an array of light-sensing pixels at the focal plane of a lens. FPAs are used most commonly for imaging purposes, but can also be used for non-imaging purposes such as spectrometry, LIDAR, and wave-front sensing.

<span class="mw-page-title-main">Infrared thermometer</span> Thermometer which infers temperature by measuring infrared energy emission

An infrared thermometer is a thermometer which infers temperature from a portion of the thermal radiation sometimes called black-body radiation emitted by the object being measured. They are sometimes called laser thermometers as a laser is used to help aim the thermometer, or non-contact thermometers or temperature guns, to describe the device's ability to measure temperature from a distance. By knowing the amount of infrared energy emitted by the object and its emissivity, the object's temperature can often be determined within a certain range of its actual temperature. Infrared thermometers are a subset of devices known as "thermal radiation thermometers".

Lead selenide (PbSe), or lead(II) selenide, a selenide of lead, is a semiconductor material. It forms cubic crystals of the NaCl structure; it has a direct bandgap of 0.27 eV at room temperature. A grey solid, it is used for manufacture of infrared detectors for thermal imaging. The mineral clausthalite is a naturally occurring lead selenide.

<span class="mw-page-title-main">Hyperspectral imaging</span> Multi-wavelength imaging method

Hyperspectral imaging collects and processes information from across the electromagnetic spectrum. The goal of hyperspectral imaging is to obtain the spectrum for each pixel in the image of a scene, with the purpose of finding objects, identifying materials, or detecting processes. There are three general branches of spectral imagers. There are push broom scanners and the related whisk broom scanners, which read images over time, band sequential scanners, which acquire images of an area at different wavelengths, and snapshot hyperspectral imaging, which uses a staring array to generate an image in an instant.

Low light level television (LLLTV) is a type of electronic sensing device, usually a CCD camera sensitive to wavelengths above the normal "visible" wavelengths, and into the short-wave Infrared - usually to about 1.0 to 1.1 micrometres. This allows viewing of objects in extremely low light levels, where they would not be seen by the naked eye. LLLTVs tend to be more affordable than infrared cameras, which typically cover ranges from 3 to 5 μm (MWIR)or 8 to 12 μm (LWIR)

A flame detector is a sensor designed to detect and respond to the presence of a flame or fire, allowing flame detection. Responses to a detected flame depend on the installation, but can include sounding an alarm, deactivating a fuel line, and activating a fire suppression system. When used in applications such as industrial furnaces, their role is to provide confirmation that the furnace is working properly; it can be used to turn off the ignition system though in many cases they take no direct action beyond notifying the operator or control system. A flame detector can often respond faster and more accurately than a smoke or heat detector due to the mechanisms it uses to detect the flame.

Thermographic inspection refers to the nondestructive testing (NDT) of parts, materials or systems through the imaging of the temperature fields, gradients and/or patterns ("thermograms") at the object's surface. It is distinguished from medical thermography by the subjects being examined: thermographic inspection generally examines inanimate objects, while medical thermography generally examines living organisms. Generally, thermographic inspection is performed using an infrared sensor.

<span class="mw-page-title-main">Infrared and thermal testing</span>

Infrared and thermal testing refer to passive thermographic inspection techniques, a class of nondestructive testing designated by the American Society for Nondestructive Testing (ASNT). Infrared thermography is the science of measuring and mapping surface temperatures.

"Infrared thermography, a nondestructive, remote sensing technique, has proved to be an effective, convenient, and economical method of testing concrete. It can detect internal voids, delaminations, and cracks in concrete structures such as bridge decks, highway pavements, garage floors, parking lot pavements, and building walls. As a testing technique, some of its most important qualities are that (1) it is accurate; (2) it is repeatable; (3) it need not inconvenience the public; and (4) it is economical."

Active thermography is an advanced nondestructive testing procedure, which uses a thermography measurement of a tested material thermal response after its external excitation. This principle can be used also for non-contact infrared non-destructive testing (IRNDT) of materials.

<span class="mw-page-title-main">Enhanced flight vision system</span>

An enhanced flight vision system is an airborne system which provides an image of the scene and displays it to the pilot, in order to provide an image in which the scene and objects in it can be better detected. In other words, an EFVS is a system which provides the pilot with an image which is better than unaided human vision. An EFVS includes imaging sensors such as a color camera, infrared camera or radar, and typically a display for the pilot, which can be a head-mounted display or head-up display. An EFVS may be combined with a synthetic vision system to create a combined vision system.

References

  1. ↑ "thermal imaging" Encarta World English Dictionary [North American Edition] © & (P) 2007 Microsoft Corporation. 17 Apr. 2008, Encarta Archived 2009-04-22 at the Wayback Machine . Archived 2009-11-01.
  2. ↑ "thermal imaging" Cambridge University Press 2008. 17 Apr. 2008, Cambridge.
  3. ↑ "tank". Encyclopædia Britannica. 2008. Encyclopædia Britannica Online. 17 Apr. 2008, Britannica.
  4. ↑ "How Night Vision Works" Howstuffworks. 17 Apr. 2008, HowStuffWorks.
  5. ↑ Hudson R. D. 1969, Infrared System Engineering, John Wiley & Sons Inc., USA.
  6. ↑ Piotrowski J. and Rogalski A. 2004, "Uncooled Long Wavelength Infrared Photon Detectors", Infrared Phys. Technol., 46:115–131.
  7. ↑ Rogalski A. and Chrzanowski K. 2002, "Infrared Devices and Techniques", Contributed Paper: Opto-electronics Review, 10(2):111–136.
  8. ↑ Ruddock W. 2004, "Infrared Imaging and Open Heart Surgery", from InfraredThermography.com by Advanced Infrared Resources [online]: accessed on June 28, 2004.
  9. ↑ Maldague X. P. 2001, Theory and Practice of Infrared Technology for Nondestructive Testing, John Wiley & Sons, N. Y.
  10. ↑ "How Stirling Engines Work" Howstuffworks. 17 Apr. 2008, HowStuffWorks.
  11. ↑ ndt.net
  12. ↑ Garziera R., Amabili M. and Collini L. "Structural health monitoring techniques for historical buildings", Proc. IV Pan American Conference in NDE, [CD-ROM], Buenos Aires, Argentina October 22–27, 2007 [available online:http://www.ndt.net/article/panndt2007/papers/141.pdf]
  13. ↑ Grinzato E. "Temperature monitors works of art health as human beings", 16th WCNDT - World Conference on Nondestructive Testing, [CD-rom], Montreal (Quebec), August 30 – September 3, 2004 [available online: http://www.ndt.net/article/wcndt2004/pdf/thermography_thermal_techniques/34_grinzato.pdf]
  14. ↑ Shepard S. M. "Flash Thermography of Aerospace Composites", Proc. IV Pan American Conference in NDE, [CD-ROM], Buenos Aires, Argentina October 22–27, 2007 [available online:http://www.ndt.net/article/panndt2007/papers/132.pdf]
  15. ↑ Avdelidis N. P., Delegou E. T. and Moropoulou A. "A thermographic survey for the monitoring porous stone", 16th WCNDT - World Conference on Nondestructive Testing, [CD-ROM], Montreal (Quebec), August 30 – September 3, 2004 [available online: http://www.ndt.net/article/wcndt2004/pdf/thermography_thermal_techniques/804_avde.pdf]
  16. ↑ "Implant gives rats sixth sense for infrared light". Wired UK. 14 February 2013. Retrieved 14 February 2013.
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