基于沙化土地变化指数的中国北方沙化土地年度动态监测分析

[Objective]The land desertification is the main concerned of the Sustainable Development Goal 15.3 land degradation neutrality.The traditional land desertification assessment methods for field surveys carry out long time period and often fails to show true situation of land desertification in time.At present,large-scale,high-spatial resolution land desertification annual dynamic monitoring is still need to be developed,which brings great difficulties to formulate the desertification control policies.This research aims to monitor and evaluate the annual changes of land desertification in the northern China based on remote sensing technology and the big earth data methods,and finally contribute to the target 15.3.[Method]The Sentinel-2 timeseries image collection is filtered,cloud removed,shadow removed with other preprocess based on the Google earth engine cloud platform from 2019 to 2020.Based on the preprocessed image collection,the annual maximum NDVI value is composited with RGB images and desertification indicators was calculated.The NDVI-Albedo feature space was constructed based on each degree of land desertification samples,The distribution of land with different degrees of desertification in the feature space was analyzed,and the annual land desertification change index was proposed and constructed.Finally,other irrelevant landcover which include water bodies,cities,and snow bodies were removed,and the annual land desertification changes in the entire northern region were evaluated based on this index.[Result]The results showed that the land area with obvious sandy land degradation trend was 39,700 square kilometers,accounting for 10.96%of the total desertification land area,and the land area with obvious sand restoration was 69,700 square kilometers,accounting for 18.95%of the total desertification area.Gansu has the highest proportion of sandy land restoration area at 27.33%,followed by Ningxia with 26.91%.Qinghai has the largest proportion of degraded sandy land at 22.55%.Gansu accounts for the largest proportion of net restoration area,with a proportion of 18.74%.[Conclusion]The net restoration area of China's desertification land is 30,000 square kilometers,indicating that China's desertification land has achieved land degradation neutrality.From the spatial distribution of desertification,the restoration trend is mainly concentrated in northern Inner Mongolia,and the degradation trend is mainly concentrated in Gansu,Shaanxi,Ningxia and other provinces.Among the 11 provinces in the study area,five provinces have achieved land desertification neutrality from 2019 to 2020.The restoration of sandy land in northern Inner Mongolia was mainly caused by the increase in vegetation coverage.The degradation of sandy land in Ningxia was mainly caused by the reduction of vegetation coverage and the desertification of cultivated land.The annual desertification characteristic index can provide information on the land desertification changes.