Brightness temperature

Shuman, C. A., Alley, R. B., Anandakrishnan, S. et al. (1995). Temperature and accumulation at the Greenland Summit Comparison of high-resolution isotope profiles and passive microwave brightness temperature trends. /. Geophys. Res. 100(D5), 9165-9177. 

When the absorbing slab is effectively very cold compared to the brightness temperature of I, notably in the interstellar case, Rc0 = 1. 

TEMPERATURE TRANSFER STANDARD. A device for the transfer of a temperature scale from one standardizing laboratory to another. One form consists of a sample of a purified material, the freezing point of which (when realized by a prescribed technique) is reproducible within narrow limits. Materials commonly employed are metals, such as zinc and tin, and organic compounds, such as benzoic acid, phenol, naphthalene, and phthalic anhydride. Another form is a tungsten ribbon-filament lamp, characterized by a stable lamp current-brightness temperature relation. This device is particularly useful for temperatures above 1.050WC. 

Microwave. Millimetre and sub-millimetre wave radiometry have been very successfully used from a variety of platforms to measure stratospheric gases. By using microwave local oscillators (LOs) and filter banks, or appropriate spectrometers, the observed brightness temperatures can be measured at various frequencies or across an emission line from a particular molecule. 

In the process of monitoring, a multitude of data series is formed, the use of which needs the establishment of correlations between the parameters of the object under study. Consider a situation that occurs under conditions of radio-physical monitoring. Let, at time moment /, at the output of each measuring device (radiometer), the values Zy (i = 1,..., M j = 1,..., rj) be fixed so that Zy 7 I , / Here 7 is the real value of the yth parameter (radio brightness temperature at wavelength A,), and Ly is the noise constituent. Search for the correlation is reduced to determination of the dependence... 

Table 5.7. Example of retrieval of brightness temperature measured over the Sarakamysh hollow (central Asia) from a flying laboratory using a microwave radiometer at the 1.35 cm wavelength.

Brightness temperature measured at 1.35 cm wavelength Retrieved brightness temperature and introduced error ... 

One advantage of a spectral radiation pyrometer is that the emissivity or emittance at only a specific wavelength (e.g. 0.653 pm) is of importance. A non-blackbody source will be less luminescent than a blackbody source at the same temperature. Thus, a falsely low temperature will be determined by sighting a calibrated disappearing filament pyrometer on the non-blackbody. This temperature has been referred to as the brightness temperature . 

A calorimetric method may be used where an electric heater is imbedded in the object of interest, and the power dissipated by the element is accurately calculated from voltage and current. Once steady state is established and the object is at constant temperature, the body must emit radiation at the same rate at which it is supplied. As long as conduction and convection are eliminated as mechanisms of heat transfer (e.g. vacuum conditions), the blackbody temperature is known by Rt = o"T4. The emittance can then be determined after py-rometric measurements of the brightness temperature of the object. 

By measuring the brightness temperature using a disappearing filament pyrometer at two wavelengths, the blackbody (actual) temperature can be calculated. 

Radiation intensities are referred to the radiation of a black body. In the radio frequency range it is convenient to express line intensities in equivalent line brightness temperatures, since the surface brightness Bv of a black body... 

In radio astronomy multichannel or autocorrelation (Fourier) spectrometers are used which simultaneously cover the whole line profile. Consider a molecular cloud observed against a source of continuum radiation of a given brightness temperature. The continuum brightness temperature is the sum of the 2.7 °K isotropic background radiation Tbh of a continuum source (such as an HII region or a supernova remnant) which may be in the line of sight and located behind the molecular cloud. A specific molecular transition with optical... 

One of the striking features of interstellar maser emission is the enormous intensity the maser lines have. In the case of water, the brightness temperature for the source W49 reaches about 1015 °K. Furthermore, the line widths of the observed lines are extremely narrow, typically only a few ten of kHz. Both properties, intense and narrow emission lines, are intrinsic indications of maser emission. It has been found that the angular size of all interstellar maser sources is very small, i.e. much smaller than the spatial resolution obtained with large single dish radiotelescopes. From long baseline interferometry, however, an upper limit has been placed on the apparent source size of about 0.002 seconds of arc (for W49 = 0.0003 , Orion = 0.001 ) (Hills et al., 1972), which, for example, at the distance of Orion, 450 pc, makes this particular water vapor source about 1/2 AU in size. This is comparable with the diameter of a red... 

Optical-pyrometer measurements are most reliable when the object being examined is the interior of a furnace or cavity of uniform temperature viewed through a small opening. Readings for an exposed surface are dependent upon the emittance e of the substance concerned, which for an ideal blackbody is unity and for actual materials is less than unity. The emittance in the visible range is near unity for carbon (e — 0.85) and oxidized metals, but it is considerably less for platinum (e = 0.3) and other unoxidized metals, especially when they are polished. The difference between the brightness temperature Tb obtained from the optical pyrometer and the actual temperature can be approximated by... 

The temperature derived from this equation is called the total brightness temperature and is measured by determining the total illumination (E) emitted by the hot source. If reabsorption by cool gases does occur then corrections must be made. 

Another possible approach uses the laboratory finding that is linearly related to the fractional area of the water surface covered by white caps (Asher et al., 1998). Since it is potentially possible to estimate white-cap coverage from the micro-wave brightness temperature of the sea surface, which can itself be measured by satellite or aircraft-borne radiometers, this may represent a way forward for the estimation of on the wide range of scales available by using these various platforms. 

Asher W., Wang Q., Monahan E. C., and Smith P. M. (1998) Estimation of air-sea gas transfer velocities from apparent microwave brightness temperature. Mar. Tech. Soc. J. 32, 32-40. 

We often measure the temperature of solid or liquid substances at high temperature by comparing them with the brilliancy or colour of the black body. This value does not show the true temperature of the substance, but this method is quite favourably used because we have no other simple method like this. The temperature which is measured by the comparison with the brilliancy of the black body is called black body temperature or brightness temperature, and with the colour of the black body colour temperature. 

Brightness temperature (K) True temperature (K) Color temperature (K)... 

Armstrong RL, Knowles KW, Biodzik MJ, Hardman MA (2003) DMSP SSM/I Pathfinder daily EASE-Grid brightness temperatures. National Snow and Ice Data Center. Digital media and CD-ROM, Boulder, CO... 

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