山丘区苹果树花期冠层反射率的定量遥感反演

采用山东省栖霞市苹果树花期不同分辨率的TM和ALOS影像,充分考虑坡向系数和冠层花叶比,通过地形辐射校正获取地表反演反射率,再经混合像元分解获取苹果树冠层的反演反射率,将30个果园样方的反演结果与同时段实测反射率及表观反射率进行比较,分析反演效果和精度.结果表明:地形辐射校正有效减弱了地形和大气的影响,恢复了阴影处地物,地表反演反射率影像的解析力大幅提高；无论是TM还是ALOS影像,冠层反演反射率的绝对误差和相对误差均最小,所有波段的相对误差表现出一致性,且样方间变化趋势与实测值最一致,说明混合像元分解是必要的.反演方法应用于不同分辨率影像,表现出相似的反射率变化特点,高分辨率图像更具优势,但受波段限制,可与中分辨率影像结合使用.

Quantitative remote sensing retrieval of apple tree canopy reflectance at blossom stage in hilly area

By using the TM and ALOS images with different resolutions at the prosperous blossom stage of apple trees in Qixia City of Shandong Province,and taking the slope aspect coefficient and the ratio of canopy flower to leaf into account,the ground surface reflectance was retrieved through radiometric correction.The canopy reflectance of the apple trees was further retrieved by pixel unmixing method,and the retrieval effect and accuracy were assessed by the comparison of the retrieved reflectance with the measured canopy reflectance and apparent reflectance of 30 sample apple orchards.The results showed that radiometric correction effectively weakened the effects of atmosphere and topography,recovered the ground objects in the shadows,and obviously enhanced the analytical ability of ground surface retrieval reflectance images.Either TM or ALOS images,both the absolute and relative errors between retrieval reflectance and measured reflectance of apple tree canopy were the smallest.The relative errors of all bands were consistent,and its variation trend among the 30 sample apple orchards was also consistent with the measured reflectance,which showed the necessary of pixel unmixing.Moreover,the changes of the reflectance among the sample apple orchards showed similar characteristics when the retrieval method was used for different resolution images.The images with high resolution were more superior,but,because of band limitation,it would be better to integrate the high resolution images with moderate resolution images.