Editing Radio window (section)

=== Troposphere ===
[[File:The Atacama Large Millimeter submillimeter Array (ALMA) by night under the Magellanic Clouds.jpg|thumb|The [[Atacama Large Millimeter Array]], an [[astronomical interferometer]] of 66 [[radio telescope]]s constructed on the 5,000 m (16,000 ft) elevation Chajnantor [[plateau]] in [[Chile]].]]
When performing observations, radio astronomers try to extend the upper limit of the radio window towards the 1 THz optimum, since the [[astronomical object]]s give [[spectral line]]s of greater intensity in the higher frequency range.<ref name=":0">{{Cite book|last1=Wilson|first1=Thomas|url=http://www.worldcat.org/oclc/954868912|title=Tools of Radio Astronomy|last2=Rohlfs|first2=Kristen|last3=Huettemeister|first3=Susanne|publisher=[[Springer Science+Business Media|Springer-Verlag GmbH]]|year=2016|isbn=978-3-662-51732-1|pages=4|language=English|oclc=954868912}}</ref> [[Troposphere|Tropospheric]] water vapour greatly affects the upper limit since its [[Electromagnetic absorption by water|resonant absorption]] frequency bands are 22.3 GHz (λ ≈ 1.32 cm), 183.3 GHz (λ ≈ 1.64 mm) and 323.8 GHz (λ ≈ 0.93 mm). The tropospheric oxygen's bands at 60 GHz (λ ≈ 5.00 mm) and 118.74 GHz (λ ≈ 2.52 mm) also affect the upper limit.<ref>{{Cite book|last=Otung|first=Ifiok|url=http://www.worldcat.org/oclc/1225565245|title=Communication engineering principles|publisher=[[Wiley (publisher)|Wiley]]|year=2021|isbn=978-1-119-27402-5|pages=390|language=English|oclc=1225565245}}</ref> To tackle the issue of water vapour, many observatories are built at high altitudes where the climate is more dry.<ref>{{Cite book|last=Karttunen|first=Hannu|url=http://www.worldcat.org/oclc/860603182|title=Fundamental astronomy|publisher=[[Springer Science+Business Media|Springer-verlag]]|year=2007|isbn=978-3-540-34143-7|location=Berlin|pages=72|language=English|oclc=860603182}}</ref> However, few can be done to avoid the oxygen's interference with radio waves propagation.<ref>{{Cite book|url=http://www.worldcat.org/oclc/25175353|title=Conference Proceedings|publisher=[[IEEE]]|year=1990|isbn=978-0-87942-557-9|pages=241|oclc=25175353 |language=en}}</ref>