The influencing factors and an error correction method of the use of infrared thermography in human facial skin temperature

This study analyzed the influencing factors of the thermal infrared imager's measurement of facial skin temperature based on infrared radiation theory, temperature measurement principle, and a proposed simplified operation range estimation method. Climate-controlled experiments were carried out to determine the influencing factors further. The experiments include nine temperature levels (12, 15, 18, 21, 24, 26, 28, 30, and 32 °C), three target-object distances (1,2 and 3 m), and two view angles (0° and 38.7°). A total of 866 valid samples from 40 participants were collected. The results revealed that the factors influencing operation range are the specifications of the infrared camera and human body height. The main factors impacting measurement are the measured skin temperature, the surrounding air temperature and the position between the camera and the human. Among them, the measured skin and air temperatures contributed 54.3% and 26.7% to the measurement difference. Compared to the distance, the influencing degree of the angle is more prominent. Considering these factors, we proposed an error correction method. The correction results show that the mean difference is −0.01 °C (95% confidence interval is −0.19 to 0.17 °C) with the 95% limits of agreement (LoA) within ±0.53 °C, which significantly reduces the original measurement difference with the mean difference of −0.58 °C (95%LoA: ±1.31 °C). The results of this study provide a theoretical basis for providing high-quality facial skin temperature data when subsequent thermal infrared imagers are used in the human body.