Research On Distribution And Vegetation Cover Grade Characteristics Of Grassland In Yunnan Province Based On Sentinel-2

Based on Sentinel-2 multispectral and digital elevation data,this paper used GEE cloud platform to study the characteristics of grassland distribution and vegetation cover grades in Yunnan province.By establishing vegetation index time series,the optimal extraction temporal and phenological information of grassland were obtained,and the grassland spectral features,gray texture features and terrain feature space were constructed.The large-scale grassland distribution information was extracted and drawn by Random Forest(RF)algorithm.Then based on this basic data map,the spatial distribution characteristics of different gradients of grassland in Yunnan province were analyzed.Finally,the grassland vegetation cover grade was evaluated by comprehensively using the size of grassland pattern area and vegetation coverage,and the spatial distribution information of grassland grade was extracted,which provided a large-scale spatial data base map for the sustainable utilization of grassland in Yunnan province and had important scientific and practical significance.The main conclusions of this study are as follows:(1)Study on distribution extraction of grassland in Yunnan province based on GEE.The NDVI time series data are compared and analyzed,and the images from February to March are selected as the basic images for extraction grassland.The spectral characteristic analysis showes that the reflectance of the grassland in B2-B8A band is significantly higher than that in the growing season,and the reflectance difference between the two seasons in B4 band is the largest.Combined with the features constructed by optimal selection,the overall classification accuracy is 0.846 and Kappa coefficient is 0.791,among which the grassland producer accuracy and user accuracy are 0.923 and 0.879 respectively.(2)In 2019,the total grassland area of Yunnan Province is estimated to be 7.17157 million hm~2 by remote sensing,which is mainly distributed in the southern subtropical,northern subtropical and temperate zones.Among them,Diqing is the most widely distributed,accounting for 10.80%,followed by Chuxiong Prefecture and Dali,accounting for 9.41%and 9.23%,and Xishuangbanna has the smallest grassland area,accounting for only 0.64%.In terms of climatic elements,Grassland is mainly distributed in the range of monthly average temperature 18.12～19.28℃,monthly average precipitation 63.99～81.23 mm,monthly average sunshine hours duration 176.66～205.75 hours.In terms of topographic elements,the grassland is mainly distributed in flat areas such as 1 800 to 2 200 m above sea level,south slope,flat land and valley bottom,etc.,but the area distribution on different slopes has little difference.(3)Grassland growth and its distribution characteristics in Yunnan province.Most of the grassland patches in Yunnan is large patches larger than 50 hm~2,which accounted for 65.57%,and mainly distributed in the northwest of Yunnan.The distribution of grassland patterns in Yunnan province is relatively discrete,showing the spatial pattern characteristics of serious fragmentation and strong habitat heterogeneity.The vegetation coverage of grassland in Yunnan province is generally high during the growing season,mainly in the range of 50-80%.The high coverage areas are mainly concentrated in northwest,northeast and eastern Yunnan,while the low coverage grasslands are mainly distributed in the economically developed and human-intensive areas in central Yunnan.(4)The grassland vegetation cover grade is classified based on the classification results of grassland pattern size and vegetation coverage in Yunnan province.It is found that the grasslands in Yunnan province are mainly medium and high-grade grasslands with high quality,of which first-class grasslands accounts for 18.48%,second-class grasslands accounts for 32.84%,third-class grasslands accounts for 43.54%,and fourth-class and fifth-class grasslands accounts for5.07%and 0.07%,respectively.The grassland production grade in Yunnan province show obvious regional differentiation characteristics,with continuous grassland distribution,high vegetation coverage and high grassland vegetation cover grade in northwest and eastern Yunnan,while scattered grassland distribution,low vegetation coverage and low grassland vegetation cover grade in central Yunnan,which mainly are hot and warm grassland.