# Dual-Channel Mapping-Gas Column Concentration Inversion Method Based on Multispectral Imaging
## 3 Experimental Verification
### Column Concentration Inversion under Different Environments
#### 3.3.2 Inversion of Gas Column Concentration under a Dynamic Environment  
In order to verify the inversion effect of this method in an actual environment, an outdoor gas column concentration inversion experiment was set up. The experiment was carried out on a sunny day with a high outdoor temperature, and the experimental scene is shown in Figure 11. SF\({}_{6}\) gas with 99.99% concentration in the gas cylinder was directly released into the atmosphere, and the concentration distribution of the gas column was retrieved using the above method. Figure 12 is a grayscale image under different channels during the operation of the exhaust in the experiment, and Figure 12a,b are gas release images of the target spectral channel and the reference spectral channel, respectively. In the image of the target spectral channel, the gas leakage position and its diffusion in the atmosphere can be observed. Since the experimental environment was outdoors and the gas diffusion was fast, the gas column concentration at the gas cylinder exhaust port was relatively high, and the gas column concentration decreased with an increase in diffusion distance. Compared with the target spectral channel, in the grayscale image under the reference spectral channel, we cannot observe the gas at all, indicating that the background image under the reference spectral channel is not affected by the target gas. The background gray image under the target spectral channel was obtained by mapping the gray image under the reference spectral channel. The absorbance distribution image of the gas was calculated in combination with Figure 12a. The absorbance distribution image was substituted into the column concentration calibration parameters to obtain a column concentration distribution image of the gas, as shown in Figure 13a. Figure 13b is  
Figure 11: Outdoor gas column concentration inversion experiment. Figure 10: (**a**) Absorbance distribution image; (**b**) column concentration distribution image. the column concentration distribution image. In Figure 13b, the maximum value of the gas column concentration is 7579.8 ppm\(\cdot\)m, and the gas column concentration is close to 0 in the background part without gas. The applicability of this method under different conditions was verified by repeating the experiments in different environments. Different scenes were selected as the gas release background, and the flow rate of gas released from the gas cylinder was reduced. The experimental results are shown in Figure 14, where Figure 14a is the experimental scene, Figure 14b is the gas release image and Figure 14c is the gas column concentration inversion image. The background of the experiment was an asphalt pavement, the temperature was 51.9 \({}^{\circ}\)C and the maximum value of gas column concentration was 6810 ppm\(\cdot\)m. In the gas column concentration distribution image, it can be clearly distinguished that the gas column concentration was high in the middle and low at both ends. In order to test the inversion effect of the system under a relatively low-temperature background, the background was replaced with a cement pavement with a lower temperature of 42.3 \({}^{\circ}\)C, and the gas release was further reduced. The inversion results are shown in Figure 15, where Figure 15a is the experimental scene, Figure 15b is the gas release image and Figure 15c is the gas column concentration inversion image. As the temperature difference between the gas and the background decreases, the system is limited by the performance of the uncooled detector, and the inversion image is fuzzy, but the  
Figure 14: (**a**) Experimental scene; (**b**) gas release image; (**c**) gas column concentration inversion image. Figure 12: (**a**) Image under the target spectral channel; (**b**) image under the reference spectral channel. Figure 13: (**a**) Image of absorbance distribution; (**b**) image of column concentration distribution. column concentration distribution of the gas can still be distinguished.