The Influence Of The Satellite Observation And Sunshine Direction On Vegetation-Shade

The research of shadow is a hot and difficult problem in the field of remote sensing. At present, the main research of shade includes shadow detection and removal, shadow algorithm and processing and so on. But, there are fewer people pay attention to the influence factor or mechanism of shadow formation. Shade is one of the most important bases to test the accuracy of vegetation cover extracted in the field of vegetation remote sensing. Based on Landsat-8 OLI data, from the point of satellite observation direction and sun exposure position, we proposed the qualitative describable model about satellite-the sun-vegetation.Based on MESMA and VIPER Tools, we took an example of Wudaoliang to Tuotuo river area and Tuotuo river to Tanggula area and we discussed the influence of satellite observation direction and sun exposure position on vegetation shadow. The conclusions are as follows:(1) According to the principle of OLI sensor imaging, satellite-the sun-the earth position in imaging time, the sun shining the earth position in imaging time, the relative location of the satellite and the earth in imaging time, the image information parameters and geographical knowledge, the qualitative describable model about satellite-the sun-vegetation in regard to the same species of vegetation at the same time and in different places and the same vegetation at different times and in the same place was put forward. In summary, in the qualitative describable model about satellite-the sun-vegetation in regard to the same species of vegetation at the same time and in different places, the length of shadow that satellite azimuth and the sun azimuth angle are opposite is more than the length of shadow that satellite azimuth and the sun azimuth angle are in the same direction. And in the same latitude,the greater longitude is, the smaller shadow is. In the qualitative describable model about satellite-the sun-vegetation in regard to the same vegetation at different times and in the same place, the length of shadow is less than the other when solar altitude is greater and imaging time is later.(2) Based on multiple endmember spectral mixing analysis arithmetic, vegetation classification abundance map, shadow abundance map, vegetation cover abundance map and soil type abundance map of typical vegetation in the research area were extracted by plug-in tool of VIPER Tools.(3) Based on extracted vegetation cover abundance and shadow abundance, the theoretical model was validated. In the qualitative describable model about satellite-the sun-vegetation in regard to the same species of vegetation at the same time and in different places, the results show that extracted Tibetan carex shade and extracted little wormwoodshade have a decreasing trend with longitude becoming larger at the same latitude, which is in the premise of similar vegetation cover and soil type as well as small RMSE. It is proved that the length of the shadow is larger when satellite observation direction and sun exposure position are in the opposite direction than that in the same direction and in the same latitude,the greater longitude is, the smaller shadow is, which is for the same species of vegetation at the same time and in different places. The results are consistent with the theoretical models.For the same vegetation at different times and in the same place, the length of shadow is less than the other when solar altitude is greater and imaging time is later, which is in the premise of a small difference of vegetation cover values and soil type values and RMSE in the overlapping areas of the two images. The results are consistent with the theoretical models.For TM data, the ranges of different vegetation shadow are not the same. Shade is influenced on satellite observations and solar radiation, but the height of vegetation itself. For the same species of vegetation, the satellite observation position and the solar altitude angle cause vegetation shadow change which is about 7%-19% in the same time and different regions.But at different time and in the same area, the satellite observation position and the solar altitude angle cause vegetation shadow change which is about 1%-9%.