Pyrometric Method of Temperature Measurement with Compensation for Solar Radiation
Outdoor remote temperature measurements in the infrared range can be very inaccurate because of the influence of solar radiation reflected from a measured object. In case of strong directional reflection towards a measuring device, the error rate can easily reach hundreds per cent as the reflected signal adds to the thermal emission of an object. As a result, the measured temperature is much higher than the real one. Error rate depends mainly on the emissivity of an object and intensity of solar radiation. The position of the measuring device with reference to an object and the Sun is also important. The method of compensation of such undesirable influence of solar radiation will be presented. It is based on simultaneous measurements in two different spectral bands, shor-twavelength and long-wavelength ones. The temperature of an object is derived from long-wavelength data only, whereas the short-wavelength band, the corrective one, is used to estimate the solar radiation level. Both bands were selected to achieve proportional changes of the output signal due to solar radiation. Knowing the relation between emissivity and solar radiation levels in both spectral bands, it is possible to reduce the measurement error several times.
Madura, H., Kołodziejczyk, M., (2005). Influence of sun radiation on results of non-contact temperature measurements in far infrared range. Opto-Electronics Review, 13, 253-257.
Bielecki, Z., Chrzanowski, K., Matyszkiel, R., Piąkowski, T., Szulim, M. (1999). Infrared pyrometer for tem-perature measurement of objects of both wavelength- and time-dependent emissivity. Optica Applicata, 29, 284-292,.
H. Madura, T. Piątkowski, E. Powiada: "Multispectral precise pyrometer for measurement of seawater surface temperature". Infrared Physics and Technology, no. 46, 2004, pp. 69-73.
Riedl, M. J., (2001). Optical Design, Fundamentals for Infrared Systems. Bellingham, Washington: SPIE Press.
Holst, G. C. (1998). Testing and Evaluation of Infrared Imaging Systems. Bellingham, Washington: SPIE Press.
Zissis, J. G. (1993). The Infrared&Electro-Optical Systems Handbook. Sources of Radiation, 1, Bellingham: SPIE Press.
Nayar, S. K., Ikeuchi, K., Kanade, T. (1989). Determining shape and reflectance of lambertian, specular, and hybrid surfaces using extended sources. International Workshop on Industrial Application of Machine Intelligence and Vision. Tokyo.
Madura, H., Kastek, M., Piątkowski, T. (2007). Automatic compensation of emissivity in three-wavelength pyrometers. Infrared Physics and Technology, 51, 1-8.
Madura, H., Piątkowski, T. (2004). Emissivity compensation algorithms in double-band pyrometry. Infrared Physics and Technology, 46, 185-189.