3D reconstruction of surface temperature field in spontaneous combustion coal gangue dump fire area and its practice

Objective The spontaneous combustion of coal gangue dumps has severely damaged the ecological environment and affected the production safety, which has become a bottleneck in the process of ecological civilization construction in China. In order to formulate a fire extinguishing plan and implement a fire extinguishing project, it is very important to accurately detect the fire area of the spontaneous combustion coal gangue dump.

Methods Herein, the idea of detecting the three-dimensional distribution of high-temperature areas using unmanned aerial vehicle (UAV) based thermal infrared oblique photogrammetry technology was proposed. Meanwhile, the multi-scale Gaussian filtering detail enhancement technology for thermal infrared image was developed to highlight the target edge information. Besides, the one-click batch processing software for thermal infrared images was created based on the FLIR Tools SDK, and the multithread asynchronous processing of thermal infrared images was efficiently carried out using ThreadPool, thereby realizing the global unification of the corresponding relationship between the color and temperature value of all thermal infrared images. Finally, the surface temperature field of fire area of the spontaneous combustion coal gangue dump was three-dimensionally reconstructed based on a batch of processed thermal infrared images. This method was also applied on the site of a burning coal gangue dump in Shaanxi Province.

Results and Conclusions  The key findings indicate that: (1) Through multi-scale Gaussian filtering detail enhancement, the detail features of the colorful thermal infrared images are significantly enhanced, and the information entropy of thermal infrared images increases from 6.989 to 7.624. (2) The developed batch processing software of thermal infrared image could quickly process 1 000 thermal infrared images within 10 minutes, greatly improving the work efficiency. (3) The above technology has been applied to successfully construct the three-dimensional surface temperature fields for two zones in a coal gangue dump fire area in Shaanxi, delineating the high-temperature areas of 11 693 m² and 10 800 m², respectively, which provides support to the assessment of the fire development trend and the creation of subsequent fire extinguishing plans. The research results could be directly applied to the three-dimensional reconstruction of temperature fields in high-temperature scenarios such as coal gangue dump fires, coal fires, landfill fires, forest fires, and building fires, providing comprehensive fire data support for fire investigation and fire source locating.