关键词: 植被覆盖度, 像元二分模型, 地形分异特征, 遥感, 崇礼区

Abstract:

Objective: Based on the results of remote sensing quantitative estimation of vegetation coverage, the temporal and spatial characteristics of vegetation coverage and topographic differentiation effects were analyzed statistically, and the driving factors of vegetation coverage changes were also discussed, which were expected to provide a reference for ecological planning, ecological environmental protection and forest fire prevention in the study area. Method: In this study, Chongli core area of Beijing Winter Olympic Games was taken as the research area, GF-1 WFV and Sentinel-2 multispectral images were used as data sources, and the pixel dichotomy method of DNVI was used to estimate the vegetation coverage of the study area in 2014, 2016 and 2020. Combined with digital elevation model, the spatial and temporal variation characteristics of vegetation cover and its topographic differentiation were analyzed by difference index, Markov model, dynamic attitude of vegetation cover and topographic distribution index. Result: 1) The spatial difference of vegetation coverage in the study area is significant, showing a pattern of low vegetation coverage in the middle and high vegetation coverage in the periphery, which is closely related to the topography and geomorphology of the whole study area. The vegetation coverage in the mountainous area is high, while that in the plain area or the mountain base is the area of human activities, and the vegetation coverage is relatively low. 2) The vegetation status of the study area was mainly dominated by middle and high vegetation coverage. In 2014, 2016 and 2020, the areas covered by the three planting grades accounted for 81.59%, 90.00% and 86.88%, respectively. The vegetation coverage of the three periods in the study area was at a good level (more than 80%), indicating that the vegetation growth status in the study area was perfect. 3) For the elevation gradient, from 2014 to 2016, the improved type and the significantly degraded type had a distribution advantage below 1 800 m, but there was no distribution advantage above 1 800 m, and the slightly degraded type had a distribution advantage below 1 700 m and above 2 000 m. From 2016 to 2020, the improved type and degraded type under 1 700 m had a distribution advantage, and the obvious degraded type showed a strong distribution advantage. From 2014 to 2020, the significantly improved type had a distribution advantage below 1 700 m and had a weak distribution advantage above 2 000 m, while the significantly degraded type showed a strong dominance distribution below 1 700 m and had no distribution advantage above 1 700 m. 4) From 2014 to 2016, the improved type had a dominant distribution on sunny and semi-sunny slopes, while the slightly degraded type had a dominant distribution on shady and semi-shady slopes. 5) From 2014 to 2016, the improved vegetation had a dominant distribution on sunny slope and semi-sunny slope, and the significantly degraded vegetation had a dominant distribution on shady slope. From 2016 to 2020, the slightly improved vegetation had a dominant distribution on sunny slope and semi-sunny slope, and the significantly degraded and slightly degraded vegetation had a dominant distribution on shady slope. Conclusion: 1) The vegetation coverage was spatially low in the middle and high in the surrounding areas. The structure of vegetation coverage among different levels in 2014, 2016 and 2020 was stable, but the local vegetation coverage was seriously degraded. The overall trend is to increase vegetation coverage. 2) The vegetation coverage of the study area showed a regular distribution at different levels of altitude, slope and aspect; there are significant differences between the types of vegetation coverage changes and topographical factors. Obviously the degraded areas gathered where the slope is less than 8° and the altitude is 1 533-1 700 m, but do not show obvious differentiation in the slope direction, mainly due to the construction land for the Winter Olympics venues. Obviously improved vegetation coverage is concentrated in sunny and semi-sunny slope areas, indicating that the effects of artificial afforestation are more obvious. 3) The focus of forest fire prevention is in the mountainous areas with a high vegetation coverage.

Key words: fraction vegetation cover(FVC), dimidiate pixel model, topographic differentiation features, remote sensing, Chongli