## 4 Experiment and Result Analysis
The radiation angle factors of the three guide vanes to the target point calculated using the three-dimensional dynamic reflection model of turbine blades proposed in this paper are shown in Table 1. The temperature of the measured point on the target blade, measured by a thermocouple, was used as the true temperature of the point. The voltage signals at seven temperature points on the target blade measured by the pyrometer in three channels (channel 1: 1500 nm; channel 2: 1600 nm; channel 3: 1700 nm) are shown in Figure 12a-c. The measurement results show that the radiation signals collected at the three guide vanes (the temperature distribution of a guide vane is uniform, so the radiation average of three points on a vane is used to represent the radiation of the entire vane) are almost equal to the radiation signals collected at the target blade for different temperatures due \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Vane 1** & **Vane 2** & **Vane 3** & **Furnace Wall** \\ \hline Angular factor & 0.2304 & 0.2246 & 0.1122 & 0.3018 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The angular factor between each part in the furnace and the target point on target blade. Figure 12: Measurement results at different temperatures of: (**a**) channel 1: 1500 nm; (**b**) channel 2: 1600 nm; (**c**) channel 3: 1700 nm. to the uniform heating of the heater. The inner wall of the furnace is the main source of heat, so its radiation is higher than that of the blades in the furnace. With reference to the measurement and calculation results in Table 2, a three-wavelength radiation temperature measurement method, based on reflection error correction, and three colorimetric temperature measurement methods are used to demodulate the temperature. The four radiation temperature measurement methods are listed in Table 3, and the inversion results and relative errors are shown in Figures 13 and 14. The three-wavelength radiation temperature measurement method based on reflection error correction proposed in this paper and the three colorimetric temperature measurement methods are listed in Table 3. The measured temperature results and relative temperature measurement errors of these radiation temperature measurement methods are compared, as shown in Figures 13 and 14. The temperature measurement error of method 2 is the smallest at 930.6 K, and the error is only 0.55%, but the temperature error is 6.09% at 1080.2 K of the target blade temperature. In method 3, when the target blade temperature is 1129.7 K, the temperature measurement error is the smallest, only 0.996%, but when the target blade temperature is 1031.3 K, it reaches 5.04%. The temperature measurement error of method 4 is the smallest when the target blade temperature is 1129.7 K, only 0.19%, but it is 6.00% when the target blade temperature is 1080.2 K. The demodulated temperature results of the three colorimetric temperature measurement methods have considerable uncertainty. Analysis shows that the temperature measurement error is mainly affected by differences in emissivity of the blade at the three wavelengths, the reflection of ambient radiation, and measurement noise. The maximum temperature error of the proposed three-wavelength radiation temperature measurement method is 2.13% when the target blade temperature is 1031.1 K. The average relative errors of the four methods are 1.20%, 2.69%, 2.82%, and 2.74%, respectively. The demodulated temperature of the proposed method is close to the real temperature and is less affected by differences in emissivity and by measurement noise. The proposed method realizes the reflection error correction of the blade surface with unknown emissivity in a radiation environment and improves the accuracy of temperature measurement.