The Reflection Characteristics of Healthy Green Leaves
- Issue S1, (1997)
Published:1997
DOI: CNKI:SUN:YGXB.0.1997-S1-007
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Published:1997
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任何植物冠层的遥感信息都是包含叶、茎、花、周围的土壤(当冠层较稀疏时)信息的信息集合体。因此,要研究植物冠层的特性需首先研究其最重要的组成成分。正如我们所知,通过植物冠层的能量变化主要是通过叶片的反射、透射、吸收来实现的,因此叶片的光学特性必须经过适当的定量化、特征化,以发展复杂的、具有可靠预测性的冠层辐射传输模型。植物冠层叶片有不同的角度,受不同入射方向的太阳光照射。一般地,冠层反射模型都假定叶片为一个漫反射体。但Rvachev和Guminetski等多人的实验表明叶片的反射在某些情况下反映出较强的镜面反射。因此叶片的反射特性可以为既有漫反射性(朗伯性)又有镜面反射性(非朗伯性)。叶片反射的朗伯性主要是由叶内部结构的多次散射引起的,并且可用朗伯定律来计算。当入射光线仅被考虑为法线或近法线方向时,镜面反射对整个反射的贡献很小,镜面反射的情况可被忽略。许多研究表明当增大入射角时,镜面反射明显,叶片反射率增大,且增加程度随叶表面特征变化而变化,这就说明镜面反射是一个叶表面现象。并且镜面反射光是极化光,这个特性使得分离镜面反射和朗伯反射成为可能。在研究植被反射时,叶片是最重要的因子,因此单叶反射特性的定性、定量研?
A remote observation of any plant canopy derives from the collective effect of all the individual component parts including leaves
stems
flowers
and the soil background when the canopy is sparse. Therefore
canopy remote signatures can best understood by characterizing at least the most important components. The most important radiative components in live vegetation are leaves. The partitioning of radiation as reflectance transmitted
or absorbed energy depends on a number of factors including leaf cellar structure
leaf pubescence and roughness
leaf morphology
and leaf surface characteristics. Reflectance from leaves can be thought of as having both Lambertian (diffuse) and nonLambertian (specular) components. The diffuse
Lambertain character of leaf reflectance emanates primarily from the interior of the leaf through multiple scattering. The specular and nonLambertain character of the leaf reflectance arises at the surface of the leaf.In this paper
we introduce a laboratory goniometer
which was designed and built to measure and model light scattered by individual plant leaves. Goniometric measurements were taken during the summer of 1995 on individual plant leaves of soybean
corn
cotton in Changchun. Source wavebands selected were VIS band (600-690nm) and NIR band (690-760nm)
and three illumination angles were used
20°
40°
and 60° from the normal on both the adaxial(top) and abaxial(bottom) side of leaves. View zenith angles are also used
20°
40°
and 60° for every incident angle. Reflected radiation was measured at 10° increments between 0° and 350° along view zenith angles and illumination angles. The polaroids of0° and 90° are used to investigate polarized reflectance of leaf in the visible and near infrared wavelength ranges. These results shows the leaf BRDF depends strongly on wavelength
and
has a marked dependence on source incidence angle
view zenith angle and view azimuth angle. The bidirectional reflectance characteristics of individual leaves should be useful in formulating mathematical representations of nonLambertian leaf properties in radiative transfer models
and this work be continued further to obtain detailed information for s variety of species and leaf conditions.
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