Improving retrieval accuracy of apple tree canopy reflectance at blossom stage by combining 6S radiometric correction with pixel unmixing method

In order to obtain approximate true reflectance of apple tree canopy, taking Qixia City in Shandong province as the study area, the ground surface reflectance was retrieved from TM image through radiometric correction based on DEM and atmospheric parameters from 6S Model. And the reflectance of apple tree canopy at blossom stage in 26 sample orchards was further retrieved using pixel unmixing method. Then the retrieval accuracy was assessed by the comparison of retrieval reflectance with measured canopy reflectance at the same time, apparent reflectance, and apparent-unmixing reflectance of 26 samples. The results showed that this method could weaken the effects caused by atmosphere and topography effectively, recover the ground objects in the shadow of the hills. So the analytical ability of ground surface retrieval reflectance images was improved obviously. Errors between canopy retrieval reflectance and measured value were the least of the four types of reflectance, while correlation coefficient between them was the highest. Moreover, the display features of canopy retrieval reflectance among samples were more similar to measured reflectance than that of the other types. It could be concluded that this retrieval method was feasible, so this study will be served as a reliable reference to obtain the base data for the apple tree management, and other similar agriculture retrieval research.