Approach method based on brightness temperature for multi-spectral thermometer

Abstract

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.i