Pyrometric method of temperature measurement with compensation for solar radiation

Outdoor remote temperature measurements in the infra red 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 m easuring 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 muc h higher than the real on e. Error rate depends mainly on the emissivity of an object and intensity of solar radia tion. 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 simultan eous measurements in two different spectral bands, short wavelength 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 radiat ion 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 bot h spectral bands, it is possible to reduce the measurement error several times. K eywords: intensity of solar radiation, emissivity, pyrometry, radiometric temperature measurements.