## 3 Results  
### Blackbody Furnace Temperature Calibration Experiment  
In this study, a 25-band multispectral camera [27] was utilized for monitoring forest fires. A single imaging can obtain 25 spectral images, revealing the radiation intensity in the band range of 658.88-949.26 nm. The parameters of the multispectral camera are shown in Table 2.  
To obtain the response characteristics of the multispectral camera under high-temperature conditions, this study conducted a temperature calibration using the HT271 blackbody furnace (China Aviation Industry Metrology Institute). The calibration was performed at 100 K intervals over the temperature range of 1973.15 K to 2973.15 K. The blackbody source had an effective emissivity of 0.9985 and an effective radiating aperture diameter of 25 mm. The calibration was carried out at a fixed distance of 50 cm. The environmental temperature of the calibration experiment was 25.6 \({}^{\circ}\)C and the air humidity was 29.2%. The test was performed after each temperature had stabilized for 5 min, and \begin{table}
\begin{tabular}{c c} \hline
**Type** & **Parameters** \\ \hline Resolution & 2048 \(\times\) 1088 \\ Sampling bit depth (bit) & 12 \\ Sensor Type & CMOS \\ Image Size (\(\upmu\)m) & 5.5 \\ Lens Focal Length (mm) & 35 \\ Number of Spectral Channels & 25 \\  & 658.88, 668.29, 687.05, 700.34, 711.78 \\  & 728.19, 739.31, 752.47, 767.36, 780.66 \\ Spectral wavelength (nm) & 788.17, 803.58, 814.62, 827.64, 841.82 \\  & 852.64, 864.40, 879.41, 889.84, 898.70 \\  & 913.20, 921.46, 931.61, 941.35, 949.26 \\ \hline \end{tabular}
\end{table} 
Table 2: Multi-spectral camera parameters. \begin{table}
\begin{tabular}{c c} \hline
**Q/kJ\(\cdot\)m\({}^{-2}\)** & **Damage Effect** \\ \hline
1030 & Ignite wood \\
592 & Death \\
392 & Seriously injured \\
375 & Third-degree burns \\
250 & Second-degree burns \\
172 & Flesh wound \\
125 & First-degree burn \\ \hline \end{tabular}
\end{table} 
Table 1: Criteria for thermal dose \(Q\) damage. the average was averaged 10 times repeatedly. The experimental setup is illustrated in Figure 3.  
Based on the calibration results, the relationship between the grayscale response values of each spectral channel and the corresponding spectral radiance under high-temperature conditions was established. The functional relationship can be expressed as:  
\[G_{i}=A_{\lambda i}L(\lambda_{i},T)+B_{i} \tag{19}\]  
The average gray value of the effective radiation region of the blackbody furnace was selected as the response value of different bands. The sampling bit depth of the multispectral camera was 12 bit, and the range of the gray value is 0-4096, which ensured that the multispectral camera had a wide temperature range after high-temperature calibration. The average gray values of the 25 bands at temperatures from 1973.15-2973.15 K are shown in Figure 4.  
Figure 5 shows the calibration curves of the gray scale value versus the spectral irradiance for 25 bands. The gray scale value and the spectral irradiance for each channel showed an approximately linear relationship. Figure 3: Schematic diagram of high temperature blackbody furnace calibration experiment. (**a**) Temperature calibration overall picture; (**b**) multispectral radiance camera (MRC) and high temperature blackbody furnace site plan. Using the linear fitting tool, the gray value-radian exitance linear fitting parameters for the 25 bands at 1973.15-2973.15 K were obtained, as shown in Table 3. The goodness of fit R\({}^{2}\) were all greater than 0.96, which made the fitting results valid. Figure 4: Response gray values of the 25-bands of the high temperature blackbody furnace at 1973.15-2973.15 K.  
Figure 5: Calibration curve; (**a**) 658.88–711.78 nm bands; (**b**) 728.19–780.66 nm bands; (**c**) 788.17–841.82 nm bands; (**d**) 852.64–898.70 nm; (**e**) 913.20–949.26 nm.