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 ?
The 31.65 GHz brightness temperatures are greater than the 23.87 GHz brightness temperatures, which is expected because the ocean's emissivity is greater at 31.65 GHz than at 23.87 GHz.
Bearing in mind that the losses of a real signal path of course are much greater than 0.01 dB, the physical temperature of the path must be measured and used for correction of the measured brightness temperature. The corresponding losses must be known to an accuracy of better than 0.01 dB and must remain stable within the same limits.
In present simulation, the spectral brightness temperatures of dust for a 3 km height in conjunction with an optical thickness of 1.0 (at infrared wavelength of 10 [micro]m, 1000 [cm.sup.-1] in wave-number) are simulated.
Since the zenith brightness temperature in the K-band are generally less than 50 K under clear sky, K-band microwave radiometer can be calibrated using the tipping calibration.
The land surface brightness temperatures at day and night were calculated using the AMSR-E (The Advanced Microwave Scanning Radiometer--EOS) data from satellite-borne passive microwave radiometer and used to calculate the criterion factors for measuring the changes in land surface temperature and emissivity.
The brightness temperature due to this noise depends on the RF frequency and elevation angle.
where T([xi], [eta]) is the brightness temperature, ([xi], [eta]) = (sin [theta] cos [phi], sin [theta] sin [phi]) the direction cosines with respect to (x,y) axes as shown in Figure 1, and ([u.sub.k,l], [[upsilon].sub.k,l]) = ([x.sub.k] - [x.sub.l], [y.sub.k] - [y.sub.l])/[lambda] the spacing between the two antennas in wavelengths.
These include radiometric uncertainties: badly corrected residual solar effects on the brightness temperature images, varying noise level depending on the pixel location within the field of view, and brightness temperature image reconstruction biases (e.g., seasonal, orbital, at land-sea transitions).
Figure 6 shows a time series of brightness temperature observations from SSM/T-2.
Deviations between model predictions brightness temperature and backscatter coefficient in active or passive microwave radiation cannot be unambiguously explained due to multiple concurrentsources of uncertainties: i) physical model limitations ii) limitations of snow characterisation iii) additional influences e.g.
Level-1A is defined as, "Reconstructed, unprocessed instrument data at sensor's full resolution, time-referenced, and annotated with ancillary information, including radiometric and geometric calibration coefficients and geo-referencing parameters (e.g., platform ephemeris) computed and appended but not applied to Level-0 data." For Level-1B, it is defined as, "Level 1A data that have been processed to sensor units (not all instruments have Level-IB source data)." For GPM, an additional Level-1 category, Level-1C, has been added for common inter-calibrated microwave brightness temperature (Tc) products from GPM constellation satellites, which is necessary to ensure no systematic differences for multi-sensor and multi-satellite precipitation retrieval algorithms such as GPM IMERG.