brightness temperature


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brightness temperature

In radio astronomy, a source of surface brightness (i.e., flux density per unit solid angle) B has a brightness temperature of T B = B λ2/(2k ), where λ is the observing wavelength and k is the Boltzmann constant. If the source of that radiation is a black body, and the observing wavelength sufficiently long, the brightness temperature will equal the temperature of the black body. In the case of an interstellar cloud, it may equal the physical temperature of the cloud if the radiation is by thermal emission and the cloud is optically thick (see optical depth). If the cloud is optically thin, the brightness temperature is reduced.

Sources that radiate by nonthermal emission can have very high brightness temperatures (>109 K). See also antenna temperature.

brightness temperature

[′brīt·nəs ‚tem·prə·chər]
(thermodynamics)
References in periodicals archive ?
Radio measurements of brightness temperatures are also highly dependent on wavelength and scattering processes (see e.
The equipment, provided by Japan's National Space Development Agency, picks up both sea surface and brightness temperatures.
Accordingly, there is no reason to expect that brightness temperatures in the second setting will be correct.
Conversely, oceanographic studies reveal that the seas can produce signals with a brightness temperature near 0 K, as demonstrated in Figure 1.
In this context the objectives of SMOS+ Cryosphere are: - Gaining and better understanding of L-band SMOS Brightness Temperature (TB) observations over snow and ice surfaces and sub-surfaces with special attention to ice sheets.