- Infrared window
The atmospheric window refers to those parts of the
electromagnetic spectrumthat are, with the earth's atmospherein its natural state, "not absorbed at all". One atmospheric window lies approximately at wavelengthsof infrared radiationbetween 8 and 13 or 14 micrometresISBN 0521339561 Houghton, J.T. The Physics of Atmospheres] .
The absorptions of the principal "natural"
greenhouse gases are concentrated in two belts. Gases such as CO2 and CH4 (along with less abundant hydrocarbons) absorb at wavelengths longer than this window due to the presence of relatively long C-H and carbonylbonds. The bonds of H2O and NH3 absorb at wavelengths shorter than 8 micrometres. Except for the bonds in O3, no bonds between carbon, hydrogen, oxygen and nitrogen atoms absorb between these two ranges. This means that most of the radiation emitted by the earth's surface at wavelengths within in the atmospheric window pass through the Earth's atmosphere without heating it; instead, this radiation is emitted into space. Without this window, the Earth would become much too warm to support life, and possibly so warm that it would lose its water as Venus did early in solar systemhistory. Thus, the existence of a window in the electromagnetic spectrum is critical to Earth remaining a habitable planet.
In recent decades, the existence of the atmospheric window has become threatened by the development of highly unreactive gases containing bonds between
fluorineand either carbonor sulfur. The "stretching frequencies" of bonds between fluorine and other light nonmetals are such that strong absorption in the atmospheric window will always be characteristic of compounds containing such bonds. This absorption is strengthened because these bonds are highly polar because of the extreme electronegativityof the fluorine atom. Bonds to other halogensalso absorb in the atmospheric window, though much less strongly.
Moreover, the unreactive nature of such compounds that makes them so valuable for many industrial purposes means that they are not removable in the natural circulation of the Earth's atmosphere. It is estimated, for instance, that perfluorocarbons (CF4, C2F6, C3F8) can stay in the atmosphere for over fifty thousand years, a figure which may be an underestimate given the absence of natural sources of these gases.
This means that such compounds have an enormous global warming potential. One
kilogramof sulfur hexafluoridewill, for example, cause as much warming as "23 tonnes of carbon dioxide" over 100 years. Perfluorocarbons are similar in this respect, and even carbon tetrachloride(CCl4) has a global warming potential of 1800 compared to carbon dioxide.
Efforts to find substitutes for these compounds are still going on and remain highly problematic.
* [http://coolcosmos.ipac.caltech.edu/cosmic_classroom/ir_tutorial/irwindows.html IR Atmospheric Window]
Wikimedia Foundation. 2010.
Look at other dictionaries:
Near-infrared window in biological tissue — The near infrared (NIR) window (also known as optical window or therapeutic window) defines the range of wavelengths where light has its maximum depth of penetration in tissue. Within the NIR window, scattering is the most dominant light tissue… … Wikipedia
Infrared vision — can be defined as the capability of biological or artificial systems to detect infrared radiation. The terms thermal vision and thermal imaging [ thermal imaging Encarta® World English Dictionary [North American Edition] © (P)2007 Microsoft… … Wikipedia
Infrared Data Association — The Infrared Data Association (IrDA) defines physical specifications communications protocol standards for the short range exchange of data over infrared light, for uses such as personal area networks (PANs).*IrDA is a very short range example of … Wikipedia
Infrared astronomy — is the branch of astronomy and astrophysics which deals with objects visible in infrared (IR) radiation. Visible radiation ranges from 400 nm (blue) to 700 nm (red). Longer wavelengths than 700 nm but still shorter than microwaves are called… … Wikipedia
Infrared homing — refers to a passive missile guidance system which uses the emission from a target of electromagnetic radiation in the infrared part of the spectrum to track it. Missiles which use infrared seeking are often referred to as heat seekers , since… … Wikipedia
Window film — Window film, also called window tint or Lustalux, is transparent plastic film or metallic laminate which is applied to glass windows specifically to reduce heat and radiation from the sun. It is available in many different compositions with… … Wikipedia
Infrared — For other uses, see Infrared (disambiguation). An image of two people in mid infrared ( thermal ) light (false color) … Wikipedia
Infrared Space Observatory — Infobox Space Telescope name = Infrared Space Observatory background = caption = organization = European Space Agency (ESA) major contractors = Aerospatiale (currently Thales) alt names = nssdc id = 1995 062A location = In decaying orbit orbit… … Wikipedia
Infrared multiphoton dissociation — Infobox chemical analysis name = Infrared multiphoton dissociation caption = acronym = IRMPD classification = analytes = manufacturers = related = Blackbody infrared radiative dissociation Electron capture dissociation Collision induced… … Wikipedia
Infrared Telescope Facility — NASA Infrared Telescope Facility Télescope IRTF de la NASA Le Infrared Telescope Facility ou IRTF de la NASA est un télescope infrarouge de 3 mètres de diamètre, situé à 4168 mètres sur le sommet du Mauna Kea. Il a été créé à l initiative de la… … Wikipédia en Français