# Dual-Channel Mapping-Gas Column Concentration Inversion Method Based on Multispectral Imaging
## 1 Introduction  
Infrared imaging gas detection technology has seen rapid development in recent years; it uses the infrared radiation absorption spectrum of gas to achieve qualitative and quantitative analyses of gas. With the advantages of long-distance, wide-ranging and rapid detection, as well as being dynamic and intuitive, it has been widely used in industrial production, environmental monitoring, national defense security and other fields [1; 2; 3; 4; 5]. Infrared imaging detection technology is mainly divided into two forms: active and passive. The active infrared gas imaging detection technology represented by the radiation absorption mode employing a laser light source has the advantages of a high signal-to-noise ratio, high detection sensitivity and no need for a temperature difference between the gas and background [6; 7; 8]. However, due to the limitations of the laser light source, it also has the disadvantages of a large volume, a narrow spectral detection range, few detectable gas types and low safety, which makes it limited in terms of practical application [9; 10; 11; 12; 13; 14]. In contrast to this, passive infrared gas imaging detection technology is a new gas detection technology that has developed rapidly in recent years. Compared with the active method, passive infrared gas imaging detection technology has the advantages of simple structure, more types of detectable gases, no active light source, etc. However, it requires a temperature difference between the measured gas and the background and a low signal-to-noise ratio, making it suitable for gas detection under harsh environments and background temperature differences [15; 16; 17; 18; 19; 20]. Currently, passive infrared gas imaging detection technology can be divided into hyperspectral imaging technology and multispectral imaging technology according to the number of detection bands. Hyperspectral imaging technology can obtain the spatial and spectral information of gases, has the ability to detect the composition of mixed gases and can detect gas column concentration more accurately. However, it also has the limitations of a complex structure, a large volume and high cost [21; 22; 23; 24]. Meanwhile, multispectral imaging technology is used to image and detect gases with absorption peaks through filters, and is widely used in the field of gas detection as it has the benefits of simple instrument structure, fast response and low cost [25; 26; 27; 28]. Nowadays, there is more and more research on multispectral gas detection technology across the world. In 2017, [PERSON] et al. developed a multi-aperture longwave-infrared multispectral imaging technique and uniquely combined, for the first time, the advantages of high throughput, real-time optimization and low cost. The applicability of this technique to the detection and classification of multiple gases is demonstrated [29]. The Gas Find IR thermal gas imager of the FLIR Company in the United States added a narrow-band filter covering the absorption peak of the target gas between the lens and the infrared focal plane. In order to improve the sensitivity of the imaging system, a variety of adjustable time integration modes were adopted, and a variety of infrared image-processing algorithms were used to achieve gas imaging detection in the narrow spectral band [30]. The above detection instrument can achieve good qualitative detection of gas leaks and distribution, but it cannot achieve the quantitative detection of gas column concentration, mainly because it is affected by the absorption of the target gas, and it is difficult to obtain accurate background radiation information. Aiming to address the problems existing in multispectral infrared gas imaging detection technology, this paper proposes a dual-channel mapping-gas column concentration inversion method based on the multispectral imaging principle.