atmospheric window

Atmospheric window. The curve shows the height above the Earth's surface at which electromagnetic radiation of different wavelengths is reduced in intensity by a factor of two. A wavelength band in the electromagnetic spectrum that is able to pass through the Earth's atmosphere with relatively little attenuation through absorption, scattering or reflection. There are two main windows: the optical window and the radio window. In the optical (or visible) region of the spectrum, wavelengths between about 300 and 900 nanometres can pass through the atmosphere. This range includes near-ultraviolet and infrared radiation, invisible to the human eye. The radio window covers the range between a few millimetres and about 30 metres in wavelength, equivalent to frequencies from 100 GHz to 10 MHz. In addition, there are a number of narrow bands in the infrared (micrometre wavelengths) and submillimetre regions in which the atmosphere is moderately transparent to radiation, particularly in geographical regions where the atmosphere is dry, since the main source of absorption at this wavelength is water molecules.