Research On The Theory And Method Of Passive Gas Leak Infrared Imaging Detection

Because of the advantages of remote sensing, quickly locating and large range detecting, Gas leak infrared imaging detection technology has become one of the most effective means to detect gas leaks. Since the passive gas leak infrared imaging detection technology has more significant advantages, such as the farther detection distance, the wider detectable spectrum, the more kinds of detectable gases and the unnecessary of the reflective background and the illumination of the radiation source, it has attracted more and more attentions from home and abroad. However, the current products of gas leak infrared imaging detection systems are mostly cooled infrared focal plane systems. Furthermore, as the imaging waveband is generally limited to media or long infrared waveband, a single system is impossible to detect the leaks of the common kinds of gases. In addition, there is no standard performance evaluation method for the gas leak infrared imaging detection systems, which have the same application purpose, while the different technical methods. The current performance evaluation methods have different defects, which cannot evaluate the gas leak infrared imaging detection systems comprehensively and accurately. What’s worse, there is no comparability of these different evaluation methods. The development of the gas infrared imaging detection technology is severely limited. Therefore, there are all-important theoretical values and realistic meanings to research the theory and key techniques of the new gas leak infrared imaging detection systems with low-cost, wideband response and relatively high sensitivity, and also the more comprehensive and accurate evaluation method.After summarizing and analyzing the development status of the passive gas leak infrared imaging detection technology home and abroad, this thesis has done in-deep study on the theory and method of the passive gas leak infrared imaging detection and has achieved some innovative results:(1) The theory of the passive gas leak infrared imaging detection is deeply studied. The radiation transfer model is studied, and the simplified conditions and forms of the layer radiation transfer model are proposed. The Gas Equivalent Blackbody Temperature Difference model is established and the influences of the background temperature, the gas temperature and concentration are simulated and analyzed. Using the computational fluid dynamics software, the characteristics of the single-point gas detection mode and the infrared imaging detection mode are simulated and analyzed. The advantages of fast detecting and precisely position the leaking source are verified.(2) The gas leak infrared imaging detection system based on the wideband uncooled focal plane detector is proposed and developed. The key technical problems are analyzed and the feasible solutions are given in this thesis. Based on the development of the wideband Uncooled Focal Plane Array(UFPA), the wideband infrared optical system, the sub-band filter and the digital imaging processing circuit, the experimental system of gas leak infrared imaging detection based on the wideband UFPA is developed for the first time, which realized wideband infrared imaging detecting the typical kinds of gases.(3) The gas leak infrared image enhancement methods based on anisotropic diffusion and bilateral filtering are proposed. For the two different application modes of fixed point monitoring and Scanning-Searching, two gas infrared image enhancement methods are proposed respectively. One focuses on highlighting the gas target and improving the interpretation ability of the human eyes; the other focuses on enhancing the faint details of the gas cloud and accurately locating the leaking source. The research and application of the two enhancement methods provide significant technical means to improve the effect of the gas infrared images for the human eyes observation, and to equivalently improve the sensitivity of the gas infrared imaging detection systems.(4) For the first time, the performance evaluation methods of Minimum Resolvable Gas Concentration(MRGC) are proposed. A set of MRGC performance measurement system for the gas leak infrared imaging detection system is developed, by which the MRGC evaluation index can be measured. The MRGC equivalent-measurement method for the gas leak infrared imaging detection system is proposed, which is able to measure the MRGC value by the MRTD measurement system of the traditional thermal imaging system and the gas infrared spectrum database. The MRGC measurement system and method are greatly simplified.Under the supports of Key project of Natural Science Foundation of Beijing and National 863 Program, this thesis has done effective research on the theory and method of the passive gas leak infrared imaging detection. Some achievements have been obtained in many aspects, such as the Gas Equivalent Blackbody Temperature Difference model,the analysis of the technical advantages, the designation of the wideband gas leak infrared imaging detection system, the gas leak infrared image enhancement method and the MRGC performance evaluation method and system. The development of the theory, technology and system of gas leak infrared imaging detection has been greatly improved. The theoretical values and realistic meanings of this research project are very important.