Study on Terrain Shadow Detection of Sentinel-2 Data Considering Water Area
Aiming at the problem that dark feature information such as water bodies affects the accuracy of ter-rain shadow extraction in mountainous areas,this paper proposes a terrain shadow extraction method based on the first principal component features and spectral features of ground objects.Firstly,the spectral features and the first principal component features of four typical ground features including topographic shadows were ana-lyzed,and the shadow component(PCA1)and the water component(NDMBWI)were established to con-struct the Normalized Shadow Index(NSI).Then,the dynamic threshold was constructed by analyzing the two-dimensional spatial distribution between NSI and NDVI.Finally,the image information is segmented to obtain the terrain shadow area.The test results show that:(1)Compared with other methods,the dynamic threshold method based on NSI has the highest overall accuracy and Kappa coefficient(about 0.893 and 0.759).The three statistics(Range,Standard Deviation,and Coefficient of Variation)of the reflectance in the shadow area are the lower,indicating that the method can effectively remove the influence of water and other dark ground objects,and accurately extract the shadow;(2)The dynamic threshold method based on NSI can ex-tract topographic shadows in different phases and different study areas with good results.The topographic shad-ows are highly distinguishable from water bodies,dark features and buildings,and can suppress the influence of cloud shadows to a certain extent.The algorithm has good stability and applicability.
Terrain shadowsShadow detectionWater bodiesShadow index
NETL
NSTL
万方数据
