question: Why are we able to see heat radiate off of things like cars and pavement.
comment: It's because of light [refracting]( URL_0 ) through the heated air just above the surface of the road. Refraction causes light (as well as other things like sound and waves) to bend when they move from one material to another. The heated air is different enough from the cooler air above it (due to density and heat expansion, etc) that the light refracts. It looks wavy like water because the way the light is being refracted changes as the boundary of the hot layer shifts due to wind and heating and stuff.
passages: 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.
   In 1966, Labrecque told "Take One" magazine, "I found I could go further in experimenting with the effects of various lenses on heat. For example, we found out how heat waves can be seen coming off the road on a hot day. We first noticed the effect approaching the camera way in the distance. With everything telescoped, it produced a unique effect. Notice how, on the right of the line of cyclists (they were on a straight road seven miles long), the telephone poles seem to be a narrow fence. In reality, there is a 180 feet between each pole.
   Temperature variations in the air can also cause refraction of light. This can be seen as a heat haze when hot and cold air is mixed e.g. over a fire, in engine exhaust, or when opening a window on a cold day. This makes objects viewed through the mixed air appear to shimmer or move around randomly as the hot and cold air moves. This effect is also visible from normal variations in air temperature during a sunny day when using high magnification telephoto lenses and is often limiting the image quality in these cases.
   A typical application for regularly available IR Thermographic equipment is looking for "hot spots" in electrical equipment, which illustrates high resistance areas in electrical circuits. These “hot spots” are usually measured in the range of 40 °C to 150 °C (70 to 270 °F) above ambient temperatures. But, when engineers use its patented proprietary systems to locate subsurface targets such as underground storage tanks (USTs), pipelines, pipeline leaks and their plumes, and in this project, hidden tunnels, we are looking for temperature patterns typically in the range of 0.01 °C to 1 °C above or below ambient temperatures. 
   Heat haze, also called heat shimmer, refers to the inferior mirage experienced when viewing objects through a layer of heated air; for example, viewing objects across hot asphalt or through the exhaust gases produced by jet engines. When appearing on roads due to the hot asphalt, it is often referred to as a highway mirage.
   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.
   There are many sources of light. A body at a given temperature emits a characteristic spectrum of black-body radiation. A simple thermal source is sunlight, the radiation emitted by the chromosphere of the Sun at around peaks in the visible region of the electromagnetic spectrum when plotted in wavelength units and roughly 44% of sunlight energy that reaches the ground is visible. Another example is incandescent light bulbs, which emit only around 10% of their energy as visible light and the remainder as infrared. A common thermal light source in history is the glowing solid particles in flames, but these also emit most of their radiation in the infrared, and only a fraction in the visible spectrum.
   This phenomenon occurs everywhere, all the time. It is a process known as radiant heat exchange, since radiant power × time equals radiant energy. However, in the case of infrared thermography, the above equation is used to describe the radiant power within the spectral wavelength passband of the thermal imaging camera in use. The radiant heat exchange requirements described in the equation apply equally at every wavelength in the electromagnetic spectrum.
   When radiative flux is incident on a surface, it is often called irradiance. Flux emitted from a surface may be called radiant exitance or radiant emittance. The ratio of irradiance reflected to the irradiance received by a surface is called albedo.
  
  Section::::Shortwave radiation flux.
   Infrared vision
  
  Infrared vision is the capability of biological or artificial systems to detect infrared radiation. The terms thermal vision and thermal imaging, 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.
   There are three ways of transferring energy: 1) conduction; 2) convection; and 3) radiation. Good solid backfill should have the least resistance to conduction of energy and the convection gas radiation effects should be negligible. The various types of problems associated with soil erosion and poor backfill surrounding buried pipelines increase the insulating ability of the soil, by reducing the energy conduction properties, without substantially increasing the convection effects. This is because dead air spaces do not allow the formation of convection currents.
   An urban heat island occurs where the combination of heat-absorbing infrastructure such as dark asphalt parking lots and road pavement and expanses of black rooftops, coupled with sparse vegetation, raises air temperature by 1 to 3 °C higher than the temperature in the surrounding countryside.
   BULLET::::- Sound refraction: Just as a submarine can use refraction to hide its acoustic signature from surface vessels, the same principle of sound refraction can be used to prevent certain observers from hearing the noise. For example, an outdoor observer close to the ground will have sound waves refracted toward him when the ground is "cooler" than the ambient air and away from him when the ground is "hotter" than the air.
   In order to have an energy flow, there must be an energy source. Since buried pipeline testing can involve large areas, the heat source has to be low cost and able to give the ground surface above the pipeline an even distribution of heat. The sun fulfills both of these requirements. The ground surface reacts, storing or transmitting the energy received.
  
  Section::::Pipeline testing.
   On the surface of Earth, at far lower temperatures than the surface of the Sun, some thermal radiation consists of infrared in the mid-infrared region, much longer than in sunlight. However, black body or thermal radiation is continuous: it gives off radiation at all wavelengths. Of these natural thermal radiation processes, only lightning and natural fires are hot enough to produce much visible energy, and fires produce far more infrared than visible-light energy.
  
  Section::::Regions within the infrared.
   Intensity can sometimes be called radiance, especially in other fields of study.
  
  The emissive power of a surface can be determined by integrating the intensity of emitted radiation over a hemisphere surrounding the surface:
  
  For diffuse emitters, the emitted radiation intensity is the same in all directions, with the result that
  
  The factor formula_11 (which really should have the units of steradians) is a result of the fact that intensity is defined to exclude the effect of reduced view factor at large values formula_8; note that the solid angle corresponding to a hemisphere is equal to formula_13 steradians.
   Section::::Police actions.
  
  In 2001, the United States Supreme Court decided that performing surveillance of private property (ostensibly to detect high emission grow lights used in clandestine cannabis farming) using thermal imaging cameras without a search warrant by law enforcement violates the Fourth Amendment's protection from unreasonable searches and seizures. Kyllo v. United States, 533 U.S. 27, 121 S.Ct. 2038, 150 L.Ed.2d 94 (2001).
   The photothermal mechanism manifests itself, besides the photoacoustic effect, also by other physical changes, notably emission of infra-red radiation and changes in the refraction index. Correspondingly, it may be detected by various other means, described by terms such as "photothermal radiometry", "thermal lens" and "thermal beam deflection" (popularly also known as "mirage" effect) (see Photothermal spectroscopy. These methods parallel the photoacoustic detection. However, each method has its special range of application.
  
  Section::::Physical mechanisms.:Other.
   The optical phenomenon occurs because rays of light are bent when they pass through air layers of different temperatures in a steep thermal inversion where an atmospheric duct has formed. (A thermal inversion is an atmospheric condition where warmer air exists in a well-defined layer above a layer of significantly cooler air. This temperature inversion is the opposite of what is normally the case; air is usually warmer close to the surface, and cooler higher up.)
   The apparent temperature difference method of defining infrared signature gives the physical temperature difference (e.g. in kelvins) between the object of interest and the immediate background if the recorded radiance values had been measured from perfect blackbody sources. Problems with this method include differences in radiance across the object or the immediate background and the finite size of the detector's pixels. The value is a complex function of range, time, aspect, etc.
  
  Section::::Contrast radiant intensity.
   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 .
   Since infrared radiation is emitted by all objects near room temperature, 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 to security services.
  
  Section::::Night vision.:Thermography.
   Although much of the literature on the subject is concerned with just one mechanism, there are actually several different mechanisms that produce the photoacoustic effect. The primary universal mechanism is "photothermal", based on the heating effect of the light and the consequent expansion of the light-absorbing material. In detail, the photothermal mechanism consists of the following stages: 
  
  BULLET::::1. conversion of the absorbed pulsed or modulated radiation into heat energy.
  
  BULLET::::2. temporal changes of the temperatures at the loci where radiation is absorbed – rising as radiation is absorbed and falling when radiation stops and the system cools.
   Section::::Reception.
  
  Reflecting on the film Noyce said:
   Weather satellites equipped with scanning radiometers produce thermal or infrared images, which can then enable a trained analyst to determine cloud heights and types, to calculate land and surface water temperatures, and to locate ocean surface features. The scanning is typically in the range 10.3–12.5 µm (IR4 and IR5 channels).
  