Lesson 1
Meteorological Satellite Orbits
Lesson 2
Review of Radiative Transfer
Lesson 3
Visible Image Interpretation
Lesson 4
Infrared Image Interpretation
Lesson 5
Multispectral Image Interpretation
Lesson 6
Fires & Aerosols
Lesson 7
Lesson 8
Lesson 9
Fog and Stratus
Lesson 10
Lesson 11
Lesson 12
Lesson 13
Global Circulation
Lesson 14
Synoptic Scale
Lesson 15
Local Circulation
Lesson 16
Satellite Oceanography
Lesson 17

Absorption and emission in gases: spectroscopy

The three major absorbing and emitting gases in the stratosphere and troposphere are ozone, carbon dioxide and water vapor. There are also important minor constituents such as CFCs and methane. While N2 and O2 are the most abundant gases in the atmosphere, from an atmospheric energetics point of view these are of small importance. The solar energy below 0.2mm is absorbed by O, NO, O2 and N2 before it reaches the stratosphere.

Ozone, O3, primarily absorbs in the ultraviolet and in the 9.6 mm region. Solar radiation in the Hartley spectral band (0.2-0.3 mm) is absorbed in the upper stratosphere and mesosphere by ozone. Absorption by O3 in the Huggins Band (0.3-0.36 mm) is not as strong as in the Hartley bands. O3 absorbs weakly in the .44 to 0.76mm region, and strongly around the 9.6mm region, where radiation is emitted by the surface.

Carbon dioxide is generally a weak absorber in the solar spectrum with very weak absorption in the 2.0, 1.6 and 1.4 mm bands. The 2.7 band is strong enough that it should be included in calculations of solar absorption, though it overlaps with H2O. The 4.3 mm band is important more in the infrared region due to the small amount of solar energy in this band. This 4 mm band is important for remote sensing atmospheric temperature profiles. CO2 absorbs significantly in the 15 mm band from about 12.5-16.7 mm (600-800 cm-1. Itis these differences in the shortwave and infrared properties of CO2 (and atmospheric water vapor) that lead to the greenhouse effect.

Water vapor absorbs in the vibrational and rotational bands (ground state transitions). In terms of radiative transfer through the atmosphere, the important water vapor absorption bands in the solar spectrum are centered at 0.94, 1.1, 1.38, 1.87, 2.7, and 3.2 mm. In the infrared, H2O has a strong vibrational-absorption band at 6.3 mm. The rotational band extends from approximately 13 mm to 1 mm. In the region between these two infrared water vapor bands is the continuum, 8-13 mm, known as the atmospheric window. The continuum enhances absorption in the lower regions of the moist tropical atmosphere.

NASA Solar spectral image


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