Angular Reflectance of Leaves With a Dual-Wavelength Terrestrial Lidar and Its Implications for Leaf-Bark Separation and Leaf Moisture Estimation
Angular Reflectance of Leaves With a Dual-Wavelength Terrestrial Lidar and Its Implications for Leaf-Bark Separation and Leaf Moisture Estimation
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DOI：
10.1109/tgrs.2017.2652140
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发表时间：
2017-06-01
影响因子：
8.2
通讯作者：
Danson, F. Mark
中科院分区：
文献类型：
--
作者：
Hancock, Steven;Gaulton, Rachel;Danson, F. Mark
新一代多波长激光雷达提供了同时测量植被的结构和生物化学的潜力，使用距离分辨光谱指数来克服被动光学测量中的混淆效应。然而，叶片的反射率取决于入射角，如果这种依赖性在波长之间变化，所得到的光谱指数也将随入射角而变化，使其在分离植被冠层的结构和生物化学效应中的应用复杂化。索尔福德高级激光冠层分析仪（SALCA）的双波长地面激光扫描仪被用来测量反射率的角度依赖性的范围内的叶片在所使用的波长由新一代的多波长激光雷达，1063和1545纳米，所使用的SALCA，DWEL，和Optech泰坦。还评估了入射角对这些波长的归一化差异指数（NDI）的影响。在两个波长的反射率取决于入射角，可以很好地模拟为余弦。与观察到的鲜叶和干叶之间以及叶和树皮之间的NDI差异相比，NDI随叶片入射角的变化较小。因此，可以得出结论，角度效应不会显着影响叶片水分检索或防止叶/树皮分离的波长中使用的新一代的1063-和1545-nm多波长激光雷达。
A new generation of multiwavelength lidars offers the potential to measure the structure and biochemistry of vegetation simultaneously, using range resolved spectral indices to overcome the confounding effects in passive optical measurements. However, the reflectance of leaves depends on the angle of incidence, and if this dependence varies between wavelengths, the resulting spectral indices will also vary with the angle of incidence, complicating their use in separating structural and biochemical effects in vegetation canopies. The Salford Advanced Laser Canopy Analyser ( SALCA) dual-wavelength terrestrial laser scanner was used to measure the angular dependence of reflectance for a range of leaves at the wavelengths used by the new generation of multiwavelength lidars, 1063 and 1545 nm, as used by SALCA, DWEL, and the Optech Titan. The influence of the angle of incidence on the normalized difference index ( NDI) of these wavelengths was also assessed. The reflectance at both wavelengths depended on the angle of incidence and could be well modelled as a cosine. The change in the NDI with the leaf angle of incidence was small compared with the observed difference in the NDI between fresh and dry leaves and between leaf and bark. Therefore, it is concluded that angular effects will not significantly impact leaf moisture retrievals or prevent leaf/bark separation for the wavelengths used in the new generation of 1063- and 1545-nm multiwavelength lidars.