What is to our knowledge a novel infrared thermometer (IRT) for remote measurement of the temperature rise (-20-100 K) above the variable ambient (270-320 K) of a distant object is described. A radiation-balancing method is successfully extended to the near-ambient temperature range by variation of the temperature of a built-in blackbody, until the radiation from it equals the radiation from the source, so that its temperature is proportional to that of the source. Another feature believed to be novel is simplifying the design by elimination of the need for cooling the blackbody for subambient temperature range by use of a second blackbody, strategically located, which is heated to achieve radiation balance. Detailed theoretical analysis is given, showing that the IRT can measure remotely the total emissivity or even the electric current or voltage. Resistive inserts are proposed for improving the accuracy of current measurement. A method is proposed for simultaneous remote measurement of absolute temperature and emissivity by variation of the heating current and the aperture of the blackbody for radiation balancing in two bands so that prior knowledge of the object's emissivity is not needed.
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