ENVR 200 Lecture Notes - Lecture 4: Background Radiation, Electromagnetic Radiation, Electromagnetic Spectrum
23 Nov 2017
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Document Summary
The sun provides the energy that powers the planet, the earth reflects some of that energy, absorbs the rest. At first glance, energy does not seem to be in balance. All objects above absolute zero(-273 c), defined by wavelength and frequency. Though electromagnetic spectrum is continuous, distinguish different types of waves. Radiation laws: wien"s law: the wavelength of the most intense radiation an object emits decrease with temperature. The surface of the sun has temperature 5780k, the earth"s surface is at 288k(15c) Terrestrial (long wave, infrared), most intense at wavelength=10u m. The earth at visible and ir wavelengths: stefan-boltzman law: energy emitted by an object is proportional to the fourth power of its temperature. Solar radiation provided the input of energy to the planet"s surface and its atmosphere(geothermal heat negligible) Some solar radiation(31%)is reflected and terrestrial radiation is emitted, balancing the budget. Atmosphere is almost transparent to solar radiation, but absorbs a significant portion of the terrestrial radiation.
