Study On Uncertainty Of Snow Information Extraction From NDSI

Snow has great significance in many scales of time and space,it is also one of theimportant factors that affect the global climate due to the low Spatial density of the groundobservation,it can’t provide sufficient snow distribution characteristics, the remotesensingsatellite data，satellite remote sensing data which takes wide application good continuity andshort information acquisition cycle as its features，has become an ideal means of continuousmonitoring of snow, and made good progress.In the arid area of China snow cover is one of the important input parameters of accuratesimulation and forecast spring runoff simulation so extract the correct information of snow isparticularly important. This research using TM images and DEM data extract snow coverinformation in the study area based on the method of NDSI and visual interpretationmethod,by virtue of the absolute uncertainty(UA)and the relative uncertainty(UR),qualitativeand quantitative analysis terrain factor and land cover factor which affect its uncertainty ofNDSI method to extract snow cover information. The main research contents and conclusionsof this paper are as follows:(1) Due to different slopes has different atmospheric condition and reflectivity， with theincrease of the slope the uncertainty of extract snow information using the method of NDSIhas generally trended down.(2)Because of in different slope direction the length of time that accept the solarradiation is different lead to snow’s thickness of shade slops and sunny slope is different.Extract snow information using the method of NDSI the uncertainty is less in shade slops andlarger in half shade slops and half sunny slopes are between the two.(3) Along with the increase of altitude, the tend of extract snow information using themethod of NDSI,the absolute is increases at first then decreases, that means in the seasonalsnow cover area,with the rise of altitude the uncertainty of extract snow information by themethod of NDSI increased, in a stable snow cover area, with the increase of altitude, itsuncertainty decreases rapidly.(4) With the decrease of the slope angle cosine (cosi), some areas that cannot receive sunilluminate directly produce significant terrain shadow,the influence of different shadow zoneis different, drop shadow area uncertainty is less than umbra area.(5) In the process of extracting snow, the surface of the cover will generate false orleakage phenomenon, by comparing the values of relative uncertainty we can found that, invegetation region the uncertainty of extract snow automatically are greater than non-vegetatedarea.