It is known from relationship between brightness temperature and true temperature of a multi-spectral thermometer that
brightness temperature is equal to true temperature if the wavelength approaches to zero. Thus true temperature can be
acquired by fitting brightness temperatures and corresponding wavelengths using non-linear least squares method. This
method was named AMBT (approach method based on brightness temperature). The emissivities of metals and nonmetals
were used to simulate AMBT at a temperature from 160K to 3000K. The effective wavelengths chosen are 3.00,
3.25, 3.50, 3.75, 4.00, 4.25, 4.50 and 4.75 micron in the atmospheric window of 3-5 micron. While in another
atmospheric window of 8-12 micron, the effective wavelengths are 8.00, 8.50, 9.00, 9.50, 10.00, 10.50, 11.00 and 11.50
micron. Actual measurements were used to verify the effectiveness of AMBT. Results show that the errors are always
smaller at a lower temperature and increase with the increase in temperature. The errors of 3-5 micron are lower than
those of 8-12 micron. At same temperature, the errors of metals are lower than those of non-metals. AMBT is more
accurate to be used at a low temperature than be used at a high temperature. AMBT can be used to identify materials in
common use, offering a new method to get true temperature of low temperature objects.ï
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