Change in temporal-spatial pattern of vegetation coverage in Weichang County based on Landsat remote sensing image

Based on the Google Earth engine remote sensing cloud platform, the Landsat series remote sensing satellite images from 1987 to 2016 were collected, and the vegetation coverage of Weichang Manchu and Mongolian Autonomous County in Chengde was estimated by using the pixel binary model, and the dynamic changes in vegetation coverage in the study area in the past 30 years were analyzed through combining the meteorological data and terrain information. The results indicate that the normalized vegetation index (NDVI) value of Weichang County from 1987 to 2016 showed an overall upward trend, and the average NDVI value of Weichang County increased from 0.63 to 0.78, and the vegetation coverage status improved continuously. Among the vegetation improvement in the study area, 49.28% of the county's vegetation area was accounted for with the NDVI difference value > 0.15 from 1987 to 2016 (with the largest proportion), while the proportion of vegetation area with NDVI difference value less than -0.15 from 1987 to 2016 was only 0.82%. The transfer matrix of vegetation coverage at all levels from 1987 to 2016 shows that the vegetation condition in 2016 was obviously better than that in 1987, and the area of vegetation with extremely high coverage was 7 991.84 km². From 1987 to 2016, the fragmentation degree of vegetation coverage landscape decreased continuously, the average patch area index increased from 13.147 8 to 31.703 4, and the vegetation coverage types tended to be centralized distribution with good connectivity. The overall climate change trend in the study area has adverse effects on vegetation growth. The vegetation coverage of different slope and aspect is different. The influence of human activities and socio-economic factors plays an important role in vegetation improvement in the study area.