Comparison of radiation temperature measurement precision between middlewave and longwave thermal-imaging systems

A comparison study on temperature measurement precision between middlewave 3-5μm and longwave 8-12μm measuring thermal imaging systems has been conducted. The study was limited to systems working in indoor conditions and the target´s temperature is in the range of 270K~900K. First, the Disturb Resisting Function (DRF) of infrared systems is deduced. On the base of DRF curve, we find that the middlewave infrared system get the smaller influences under the same size disturb compared with the longwave system. A theory of the influence of target´s physical characteristic and measurement conditions on the accuracy of temperature measurements has been developed. On the basis of the developed formulas an analysis of the influence of signal disturbances (because of incorrectly assumed emissivity, limited transmittance of the atmosphere, radiation reflected by the object and shift of optics radiation) on the accuracy of temperature measurement has been made. It has been found that the middlewave systems in typical temperature range offer generally better accuracy in temperature measurement than the longwave ones do.