thermal emission


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thermal emission

(thermal radiation; thermal bremsstrahlung) Electromagnetic radiation resulting from interactions between electrons and atoms or molecules in a hot dense medium. The term usually refers to thermal emission from ionized gas (but see also thermal black-body radiation). Free electrons in the ionized gas radiate when they are deflected in passing near protons. The electrons are unbound to a nucleus before and after each encounter and the radiation is therefore also known as free-free emission. The radiation has a continuous spectrum, which at low frequencies has the spectral index, α, of a thermal black-body radiator, i.e.
S ∝ ν–α; α = –2
where S is the flux density and ν the frequency. At higher frequencies the spectrum flattens to a spectral index of α = 0. The emission measure of an ionized region of length l containing a density n e of free electrons is given by
EM = l 0 n e 2 ds
where ds is an element of the path through the region. Compare nonthermal emission.
References in periodicals archive ?
In fact, Guo et al point out that Kirchhoff's Law still suffices to calculate the thermal emission in the far-field and that "the high-k waves which are thermally excited in the HMM are trapped inside and will be evanescent in vacuum (not reach the far field)" [14, p.
The measurement of the whole atmospheric thermal emission spectral range allows one to obtain information about the relevant atmospheric components, which contribute to the longwave energy balance.
In order to prove the hypothesis experimental research and simulation of the structure behavior applying thermo graphic and thermal emission methods was performed.
ASU also developed two miniature thermal emission spectrometers (Mini-TES) for the Mars Exploration Rovers, Spirit and Opportunity.
Pictures were beamed back from a Thermal Emission Imaging System (THEMIS) camera on the Mars Odyssey probe.
To assist them, each rover has housed in its body a miniature thermal emission spectrometer that can detect the unique thermal profiles produced by different types of rocks and soil, allowing them to determine mineral components from a distance.
In order to survey conditions, the rovers are equipped with panoramic TV cameras, a magnet array, an alpha particle x-ray spectrometer, a Mossbauer spectrometer, a microscopic imager, and a small thermal emission spectrometer.
The orbiting spacecraft has turned on its thermal emission imaging system and gamma ray spectrometer instruments have begun collecting data on the composition of the Martian surface.
He said this was evidenced by their four joint satellite projects -- the Tropical Rainfall Measuring Mission, the Japanese Earth Resources Satellite, the Advanced Earth Observing Satellite, and the Advanced Spaceborne Thermal Emission and Reflection Radiometer.
The Advanced Spaceborne Thermal Emission and Reflection Radiometer, or ASTER, instrumentation takes high-resolution images of the Earth--15 to 90 meters--in the visible near-infrared, short-wave infrared, and thermal infrared regions of the spectrum.
A thermal emission spectrometer measures how much heat Martian rocks emit.
Because the body's layer of fat provides insulation and prevents adequate thermal emission, the skin surface, such as the forehead and axila, cannot provide accurate thermal measurement.