Blackbody simulators

In the article humorously titled Blackbody, blackbody simulator, blackbody simulator cavity, blackbody simulator cavity aperture, and blackbody simulator aperture are each different from one another, Bartell (1989b) points out important conceptual differences that should be recognized but are generally overlooked when we speak of BBS. A (true) BB is an idealization. The devices in our laboratories that we call BBS are actually blackbody simulators. One type uses an approximately isothermal cavity and a separate aperture. For a well-designed simulator, accurate radiometric calculations can be done by fleating that separate aperture (not the cavity itself, nor the cavity opening) as the IR source. The IR irradiance depends on the distance from the separate aperture. 

Bartell (1989b) Blackbody, Blackbody Simulator, Blackbody Simulator Cavity, Blackbody Simulator Cavity Aperture, and Blackbody Simulator Aperture are Each Different from One Another by F. O. Bartell, Proc SPIE, 1110, 183. 

The most common source for IR work is a blackbody, and a blackbody is the obvious choice whenever it will generate acceptable signal levels at obtainable temperatures. A well-made cavity blackbody (technically a blackbody simulator) has an emissiv-ity so close to unity that we can safely assume that value. It requires no calibration except that required for the temperature sensors. Given the cavity temperature and the area of the separated aperture, Planck s radiation law yields the exitance and irradiance - both as a function of wavelength, and integrated over any desired spectral region. These were discussed in Chapter 2. Mounting and calibration of blackbodies is discussed in Section 9.3.1. 

The most common source for detector testing in the 3-20 pm region is a cavity type blackbody simulator - a heated cavity with diffuse walls and a large wall area-to-opening ratio. To the extent that such a cavity simulates a true blackbody, its exitance can be predicted using Planck s law this is discussed in Chapter 2. Hereafter, we will follow convention and refer to such a cavity simply as a blackbody. Blackbodies rely on multiple internal reflections to achieve effective emissivities of 0.99 and more. 

At this point, we consider Equation (A3.1), which is only valid for pure monochromatic incident radiation. As we are dealing with blackbody radiation, we simulate the elemental density of radiation Paidco by monochromatic radiation that has the same power. According to Equation (A3.1), the corresponding probability of elemental transition (absorption or stimulated emission) dP is as follows ... 

Comment by Author The analogy pointed out by D. J. Santeler is certainly correct and can be used to advantage in the design of space solar simulation systems. A collimated solar radiation beam is analogous to a high gas-speed ratio, w hereas, a diffuse radiation source, such as blackbody radiation from a large test article is equivalent to the random diffuse gas case. 

In SkyParams.xlsx the user defines the sky map to be created if no science input map is used. The first sheet in the file is the one that the simulator reads, so different configurations can be stored in the same file. The first option is the Full Width Half Maximum (FWHM) if empty, a point source is created, if full, a Gaussian source is simulated with this FWHM. The user may input the source position in the sky at jc j)os and y j)os. If empty the simulator will display a sky grid where the user selects the position or a source by clicking on that position. Temp is for the temperature in Kelvin of a Blackbody spectrum, cut-on and cut-off will filter the Blackbody spectrum at the wavenumbers given at these parameters. For verification purposes, if the user inputs 1 the spectrum for that given source will be the one measured with the Cardiff-UCL FIRI testbed. If the user inputs 0 the spectrum will consist of a single wavenumber tone, defined at tone wl. 

Figure4.3 shows an example of a simulated datacube, where 4 sources have been positioned on the sky grid (left) two gaussian sources, and two point sources. The spectra of these sources are different, corresponding to blackbodies of different temperatures which have been multiplied by Alters with different cut-on and cut-off wavenumbers (right). For the loading of more complex sky map data cubes such as science datacubes the simulator will interpolate or decimate to meet the instrument parameters.

Fig. 5.20 Spectra generated with the Sky Simulator for the source consisting of a blackbody at 1800 K with cut-on and cut-off wavenumbers of 5cm and 33cm respectively and attenuated by the atmosphere (left) and the same source with the 21 cm low-pass filter (right)...

A gas turbine combusion chamber can be simulated as a long tube (0.4-m diameter surface temperature of 500°C. The flowing combustion gas at 1 atm and 1000°C contains carbon dioxide and water vapor (both mole fractions are 0.15). If the chamber surface is a blackbody, what is the net radiative flux ... 

BGO crystals with eulithine structure have a very small absorption coefficient in the wavelength band where the main part of the blackbody radiation is concentrated. In contrast to this, the absorption coefficient of sillenite crystals reaches 0.3-0.4cm in the wavelength range from 2 to 6 tm. One can expect that absorption and emission of radiation by a crystal appreciably influence the heat-transfer process. Two growth processes were simulated. The first was performed in the setup used for the growth of BGO eulithine crystals, while the second was carried out in the Laboratory of Crystal Growth of the Autonomic University of Madrid. Results of simulation are described in Refs. [38, 45], respectively. Here, we focus on the second process. 

If a larger source area is desired, or if you want to simulate the spectral content typical of many imaging applications, then extended-area ( flat-plate ) blackbodies work well. For these, it is common to assume an emissivity of 100%, but 95% is probably a better estimate. 

Background is, by definition, the irradiance level that remains when the source (usually blackbody) irradiance is set to zero. In low-background testing, we may use a blackbody to cause an irradiance level that simulates the background at which the detector will operate in another application. In this case, we would use the apparently contradictory expression the background due to the blackbody. ... 

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