The various components of the Earth's atmosphere act to reduce or completely block certain wavelengths of the radiation incident at upper levels. The principal active atoms are oxygen and nitrogen, and molecules of oxygen, ozone (in the ultraviolet), and water vapour (in the infrared). The overall spectrum at ground level is complex, but there are major windows where a significant amount of radiation reaches the surface. The most important are in the visible spectrum between about 0.3 and 0.9 μm (300 and 900 nm); multiple windows in the infrared between about 1.25 and 30 μm, and also beyond 300 μm; and at radio wavelengths between about 1 cm and 30 m.
Subjects: Meteorology and Climatology.