Forest fire analysis in Jinyun Mountain based on "star-machine-ground" technology
[Background] The investigation of burned areas after forest fires is a key and difficult point in the field of forest fire research. Traditional manual on-site investigation methods, satellite remote sensing images, and drone technology, as common investigation methods, have their own drawbacks when used alone, which cannot solve the problem of quickly and accurately dividing the severity of large-scale forest fires. Therefore, taking the location of the Chongqing Jinyun Mountain fire in September 2022 as the experimental area, and combining the advantages of the above three methods, a "star machine ground" forest fire investigation system is constructed. [Methods] Selecting mildly, moderatly, and severely fire plots, and ruler processing and mapping for each wood was conducted. Based on satellite remote sensing and unmanned aerial vehicle remote sensing images of the survey area, NDVI was calculated and spatially matched with the measured tree height, chest diameter, scorch height, and crown width of the plots. Grey correlation analysis was conducted to analyze the correlation between various indicators of the sample plots with different degrees of fire and NDVI values, and then NDVI values were extended to satellite images. [Results] 1) According to ground survey data, the scorch height of trees in each fire plot increased with the increase of fire severity. The changes in the average values of tree height and diameter at breast height were consistent, with moderate fire being the largest, mild fire being the second, and severe fire being the smallest. The average change trend of crown diameter was different from these two items, with moderate fire being the largest, followed by severe fire, and mild fire being the smallest. Large fires mainly occur in the lower layers of the forest. 2) The relationship between the four indicators of the three plots and their NDVI was above 0.55. The scorch height, crown diameter, and crown diameter indicators of the moderately burned plots were moderately correlated with their NDVI. The correlation between the tree height, DBH, and the height of the lightly burned plot and their NDVI was above 0.8, indicating a strong correlation. The correlation degree of other indicators was between 0.6 and 0.8, indicating a strong correlation. 3) Using the NDVI threshold of drone multispectral images as the standard, the NDVI ranges for severe, moderate, and mild fires were determined to be 0-0.245 6,>0.245 6-0.347 1, and >0.347 1-0.690 0, respectively. [Conclusions] Through the method of grey correlation analysis, the correlation between UAV NDVI and four ground survey data is strong, that is, the accuracy of UAV image NDVI is verified with ground survey data validation, indicating that NDVI can be used as the basis for forest fire grading. And using the NDVI threshold of each fire plot in the drone multispectral image as the standard to reclassify satellite remote sensing images of forest fire areas, it can achieve rapid and accurate classification of large-scale fire degree levels. On this basis, the soil type, dominant tree species and elevation data of different fire grades are analyzed, which is of great significance to the cause of fire and the restoration of ecological environment after forest fire.
ZHANG Xingcun, CHENG Yumeng, LI Tong, QI Zihan, HE Xiangchang, LUO Pizhao, WANG Yujie, WANG Yunqi
Dynamic mechanism of river bank stability and analysis of ecological support scheme
[Background] In order to study the dynamic mechanism of bank stability under the condition of rainfall combined with water level fluctuation, a reasonable ecological slope protection scheme was designed. [Methods] In this study, the combination of field investigation, mechanical test and numerical simulation was used to reveal the characteristics of the slope stability changing with water level and the failure mechanism of the slope in the Beibei section of the Jialing River, and the key technical parameters of the "living wood pile slope protection" measures were discussed by comparing with traditional plant slope protection methods and engineering pile slope protection methods. [Results] 1) The stability of the river bank beach slope fluctuated with the rise and fall of water level, and the slope stability dropped rapidly during the water level fluctuation stage. The reason is that the external hydrostatic pressure of the slope unloaded with the rise and fall of water level, and the seepage pressure inside the slope pointing outward from the slope caused shallow damage to the middle slope. In summer and autumn, when the water level of the river dropped more than 3 m/d, the early warning of landslide disaster on the river bank and beach should be triggered. 2) When the live wood pile, pile diameter and pile angle were fixed, properly increasing the pile length and reducing the pile spacing will help limit the horizontal displacement of the slope. It was suggested that the pile configuration of the gentle slope of the river bank beach was the middle upper part between the warning water level and the normal water level, with the pile spacing D=2.3 m, pile length L=3.3 m. The stability of topsoil will be affected only when the pile length was closed to the potential sliding layer. 3) At the initial stage of the configuration of live wood piles under the optimized parameter configuration, the stability coefficient increased by 18.6% under the extreme conditions of water level fluctuation, which was 3.8 times of the effect of traditional grass and shrubs on slope consolidation. After the root system of wood piles was fully grown, the slope stability coefficient increased by 22.3%, which was 3.7% more than that of piles configured with the same configuration. [Conclusions] This paper studied the change of pore water pressure of bank slope under the conditions of rainfall and water level fluctuation, and compared the slope stability of different support measures of bank slope in the Jialing River section of the Three Gorges Reservoir. On this basis, the arrangement parameters of movable wooden piles were optimized to provide theoretical basis and technical support for the ecological protection of the riverside in the Three Gorges Reservoir area.