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The Earth's surface absorbs visible radiation from the sun and re-emits much of the energy as infrared back to the atmosphere. Certain gases in the atmosphere, chiefly water vapor, absorb this infrared, and re-radiate it in all directions including back to Earth. This, the greenhouse effectThe greenhouse effect is the process by which an atmosphere warms a planet. Mars, Venus and other celestial bodies with atmospheres (such as Titan) have greenhouse effects, but for simplicity the rest of this article will refer to the case of Earth. The t, keeps the atmosphere and surface much warmer than if the infrared absorbers were absent from the atmosphere.

1 Different regions in the infrared

IR is often subdivided into:

• near infrared NIR, IR-A DINDeutsches Institut fur Normung (DIN, the German Institute for Standardization) is a German national organization for standardization. DIN and mini-DIN connectors are familiar to computer users all over the world, but DIN issues standards in any conceivabl, 0.7–1.4  µmA micrometre ( American spelling: micrometer , symbol m is an SI unit of length. It is defined as one millionth of a metre (1×10−6 m), equivalent to one thousandth of a millimetre. The symbol µ ( Unicode character U+00B5; HTML µ) is the " micr in wavelength, defined by the water absorption, and commonly used in fiber optic telecomunication because of the low attenuation losses in the SiO₂ glass medium.
• short wavelength IR SWIR, IR-B DINDeutsches Institut fur Normung (DIN, the German Institute for Standardization) is a German national organization for standardization. DIN and mini-DIN connectors are familiar to computer users all over the world, but DIN issues standards in any conceivabl, 1.4–3 µm Water absorption increases significantly at 1450 nm
• mid wavelength IR MWIR, IR-C DINDeutsches Institut fur Normung (DIN, the German Institute for Standardization) is a German national organization for standardization. DIN and mini-DIN connectors are familiar to computer users all over the world, but DIN issues standards in any conceivabl, also intermediate-IR (IIR), 3–8 µm
• long wavelength IR LWIR, IR-C DINDeutsches Institut fur Normung (DIN, the German Institute for Standardization) is a German national organization for standardization. DIN and mini-DIN connectors are familiar to computer users all over the world, but DIN issues standards in any conceivabl, 8–15 µm)
• far infrared FIR, 15–1000 µm

However, these terms are not precise, and are used differently in various studies i.e. near (0.7–5 µm) / mid (5–30 µm) / long (30–1000 µm). Especially at the telecom-wavelengths the spectrum is further subdivided into individual bands, due to limitations of detectors, amplifiers and sources. Infrared radiation is often linked to heatCommonly, heat is estrus, a period of increased sexual drive in female mammals. For the National Basketball Association team, see Miami Heat. For the movie, see Heat (movie). Heat (abbreviated Q also called heat change is the transfer of thermal energy be, since objects at room temperature or above will emit radiation mostly concentrated in the mid-infrared band (see black body). The common nomenclature is justified by the different human response to this radiation (near infrared = the red you just cannot see, far IR = thermal radiation), other definitions follow different physical mechanisms (emission peaks, vs. bands, water absorption) and the newest follow technical reasons (The common Si-detectors are sensitive to ~1050 nm, while InGaAs sensitivity starts around 950 nm and ends between 1700 and 2200 nm, depending on the specific configuration). Unfortunately the international standards for this specifications are not freely available.