question: How do thermal cameras work and how can they determine temperature from a distance?
comment: Objects above absolute zero emit infrared radiation. That's electromagnetic radiation, just like visible light, except your eyes don't have sensors that can detect it. The camera does. So when the 'invisible light' hits the camera, it is designed to display them in colors we can make sense of, varied by intensity. So an object emitting a lot of infrared radiation (it's hot) might show up as red, while an object emitting a little (its cool) could show up as blue.
passages: BULLET::::- Nondestructive testing
  
  BULLET::::- Surveillance in security, law enforcement and defence
  
  BULLET::::- Chemical imaging
  
  BULLET::::- Volcanology
  
  BULLET::::- Building
  
  Thermal imaging cameras convert the energy in the infrared wavelength into a visible light display. All objects above absolute zero emit thermal infrared energy, so thermal cameras can passively see all objects, regardless of ambient light. However, most thermal cameras only see objects warmer than .
   Some physiological activities, particularly responses such as fever, in human beings and other warm-blooded animals can also be monitored with thermographic imaging. Cooled infrared cameras can be found at major astronomy research telescopes, even those that are not infrared telescopes.
  
  Section::::Types.
  
  Thermographic cameras can be broadly divided into two types: those with cooled infrared image detectors and those with uncooled detectors.
  
  Section::::Types.:Cooled infrared detectors.
   Non-specialized CCD and CMOS sensors have most of their spectral sensitivity in the visible light wavelength range. However, by utilizing the "trailing" area of their spectral sensitivity, namely the part of the infrared spectrum called "near-infrared" (NIR), and by using off-the-shelf CCTV camera it is possible under certain circumstances to obtain true thermal images of objects with temperatures at about and higher.
   The thermal imaging camera would next employ a series of mathematical algorithms. Since the camera is only able to see the electromagnetic radiation that is impossible to detect with the human eye, it will build a picture in the viewer and record a visible picture, usually in a JPG format.
  
  In order to perform the role of non-contact temperature recorder, the camera will change the temperature of the object being viewed with its emissivity setting.
   Uncooled thermal cameras use a sensor operating at ambient temperature, or a sensor stabilized at a temperature close to ambient using small temperature control elements. Modern uncooled detectors all use sensors that work by the change of resistance, voltage or current when heated by infrared radiation. These changes are then measured and compared to the values at the operating temperature of the sensor.
   Thermographic camera
  
  A thermographic camera (also called an infrared camera or thermal imaging camera or infrared thermography) is a device that forms a heat zone image using infrared radiation, similar to a common camera that forms an image using visible light. Instead of the 400–700 nanometre range of the visible light camera, infrared cameras operate in wavelengths as long as 14,000 nm (14 µm). Their use is called thermography.
  
  Section::::History.
  
  Section::::History.:Discovery and research of infrared radiation.
   In addition, there are two approaches in thermographic inspection: (1) "passive", in which the features of interest are naturally at a higher or lower temperature than the background, for example: the surveillance of people on a scene; and (2) active, in which an energy source is required to produce a thermal contrast between the feature of interest and the background, for example: an aircraft part with internal flaws.
   In uncooled detectors the temperature differences at the sensor pixels are minute; a 1 °C difference at the scene induces just a 0.03 °C difference at the sensor. The pixel response time is also fairly slow, at the range of tens of milliseconds.
   Images can be difficult to interpret accurately when based upon certain objects, specifically objects with erratic temperatures, although this problem is reduced in active thermal imaging.
  
  Thermographic cameras create thermal images based on the radiant heat energy it receives . As radiation levels are influenced by the emissivity and reflection of radiation such as sunlight from the surface being measured this causes errors in the measurements. 
  
  BULLET::::- Most cameras have ±2% accuracy or worse in measurement of temperature and are not as accurate as contact methods.
  
  BULLET::::- Methods and instruments are limited to directly detecting surface temperatures.
  
  Section::::Applications.
   Infrared radiation can be used to remotely determine the temperature of objects (if the emissivity is known). This is termed thermography, or in the case of very hot objects in the NIR or visible it is termed pyrometry. Thermography (thermal imaging) is mainly used in military and industrial applications but the technology is reaching the public market in the form of infrared cameras on cars due to the massively reduced production costs.
   In order to make a temperature measurement of an object using an infrared imager, it is necessary to estimate or determine the object's emissivity. For quick work, a thermographer may refer to an emissivity table for a given type of object, and enter that value into the imager. The imager would then calculate the object's contact temperature based on the value entered from the table and the object's emission of infrared radiation as detected by the imager.
   For use in temperature measurement the brightest (warmest) parts of the image are customarily colored white, intermediate temperatures reds and yellows, and the dimmest (coolest) parts black. A scale should be shown next to a false color image to relate colors to temperatures. Their resolution is considerably lower than that of optical cameras, mostly only 160 x 120 or 320 x 240 pixels, although more expensive cameras can achieve a resolution of 1280 x 1024 pixels. Thermographic cameras are much more expensive than their visible-spectrum counterparts, though low-performance add-on thermal cameras for smartphones became available for hundreds of dollars in 2014. Higher-end models are often deemed as dual-use and export-restricted, particularly if the resolution is 640 x 480 or greater, unless the refresh rate is 9 Hz or less. The export of thermal cameras is regulated by International Traffic in Arms Regulations.
   In principle, superconducting tunneling junction devices could be used as infrared sensors because of their very narrow gap. Small arrays have been demonstrated. They have not been broadly adopted for use because their high sensitivity requires careful shielding from the background radiation.
  
  Superconducting detectors offer extreme sensitivity, with some able to register individual photons. For example, ESA's Superconducting camera (SCAM). However, they are not in regular use outside of scientific research.
  
  Section::::Types.:Uncooled infrared detectors.
   In June 2014, the Canadian National Aerial Surveillance Program DHC-8M-100 aircraft mounted with infrared sensors was instrumental in the search for Justin Bourque, a fugitive who had killed three Royal Canadian Mounted Police members in Moncton. The plane's crew used its advanced heat-sensing camera to discover Bourque's heat signature in the deep brushwoods at midnight.
   Cooled detectors are typically contained in a vacuum-sealed case or Dewar and cryogenically cooled. The cooling is necessary for the operation of the semiconductor materials used. Typical operating temperatures range from 4 K to just below room temperature, depending on the detector technology. Most modern cooled detectors operate in the 60 K to 100 K range, depending on type and performance level.
   Section::::History.:Smart sensors.
   Infrared energy is just one part of the electromagnetic spectrum, which encompasses radiation from gamma rays, x-rays, ultra violet, a thin region of visible light, infrared, terahertz waves, microwaves, and radio waves. These are all related and differentiated in the length of their wave (wavelength). All objects emit a certain amount of black body radiation as a function of their temperature.
   Without cooling, these sensors (which detect and convert light in much the same way as common digital cameras, but are made of different materials) would be 'blinded' or flooded by their own radiation. The drawbacks of cooled infrared cameras are that they are expensive both to produce and to run. Cooling is both energy-intensive and time-consuming.
   Specialized thermal imaging cameras use focal plane arrays (FPAs) that respond to longer wavelengths (mid- and long-wavelength infrared). The most common types are InSb, InGaAs, HgCdTe and QWIP FPA. The newest technologies use low-cost, uncooled microbolometers as FPA sensors. Their resolution is considerably lower than that of optical cameras, mostly 160x120 or 320x240 pixels, up to 1280 x 1024 for the most expensive models. Thermal imaging cameras are much more expensive than their visible-spectrum counterparts, and higher-end models are often export-restricted due to the military uses for this technology. Older bolometers or more sensitive models such as InSb require cryogenic cooling, usually by a miniature Stirling cycle refrigerator or liquid nitrogen. 
   Infrared light falls into two basic ranges: "long-wave" and "medium-wave". Long-wave infrared (LWIR) cameras, sometimes called "far-infrared", operate at 8 to 12 μm and can see heat sources, such as hot engine parts or human body heat, several kilometers away. Longer-distance viewing is made more difficult with LWIR because the infrared light is absorbed, scattered, and refracted by air and by water vapor.
   Remote sensing and thermographic cameras are sensitive to longer wavelengths of infrared (see ). They may be multispectral and use a variety of technologies which may not resemble common camera or filter designs. Cameras sensitive to longer infrared wavelengths including those used in infrared astronomy often require cooling to reduce thermally induced dark currents in the sensor (see Dark current (physics)). Lower cost uncooled thermographic digital cameras operate in the Long Wave infrared band (see Thermographic camera#Uncooled infrared detectors). These cameras are generally used for building inspection or preventative maintenance but can be used for artistic pursuits as well, such as this image of a cup of coffee.
   A PMMW camera is a thermal camera similar in principle to a FLIR: the black-body radiation from objects, which depends on their temperature and surface properties (such as emissivity), is captured through a lens and focused on the sensor, and then converted to an electrical signal. The difference from FLIR is the scales involved. The energy at millimetric wavelengths is much smaller than energy at 8–14 microns, the technology to capture the photons is different, and the physical size of the camera is much larger.
  
  Section::::Technology.:Sensors.:Imaging radar.
   Infrared thermography, thermal imaging, and thermal video, are examples of infrared imaging science. Thermal imaging cameras detect radiation in the infrared range of the electromagnetic spectrum (roughly 900–14,000 nanometers or 0.9–14 µm) and produce images of that radiation, called "thermograms".
   Thermal images, or thermograms, are actually visual displays of the amount of infrared energy emitted, transmitted, and reflected by an object. Because there are multiple sources of the infrared energy, it is difficult to get an accurate temperature of an object using this method. A thermal imaging camera is capable of performing algorithms to interpret that data and build an image. Although the image shows the viewer an approximation of the temperature at which the object is operating, the camera is actually using multiple sources of data based on the areas surrounding the object to determine that value rather than detecting the actual temperature.
   Although most effort to date has been focused on thermal expansion measurements, this might change. Truly robust thermal probes have recently become available, as have affordable compact QCL’s that are tuneable over a broad frequency range. Consequently, it may soon be the case that thermal probe techniques will become as widely used as those based on thermal expansion. Ultimately, instruments that can easily switch between modes and even combine them using a single probe will certainly become available, for example, a single probe will eventually be able to measure both temperature and thermal expansion.
  
  Section::::Recent improvements in AFM-IR.
  