用多角度遥感观测和BRDF模型对植物状况诊断评估(英文)

Diagnostic Assessments of Plant Condition Using Multiangular Remote Sensing Measurements and BRDF Models

用遥感技术进行植物评估可与光谱植被指数联系起来，如规一化差分植被指数ＮＤＶＩ。ＮＤＶＩ值的变化一般被认为是植被数量和密度的变化，但直接与植物生长状况有关的植物光谱特性也会导致光谱植被指数的变化。因此，低植被指数可能由于低密度或肥料不足二者之一或共同造成。这会限制植被指数作为监测手段的使用。二向反射分布函数ＢＲＤＦ模型把植物密度和光学特性区别对待，因而它有助于植物状况的客观评估。在这项研究中，我们测量了两个冬小麦冠层多角度光谱反射：一个氮肥充足，一个贫乏。这些测量随后用于ＢＲＤＦ的反演，来估计光学特性和植物密度。结果表明，同时获得这两种参数是可行的。因此，用ＢＲＤＦ和多角度遥感测量手段进行氮肥养料有关的植物状况诊断分析是可能的。结果也显示出这种方法中如反演和计算时间所带来的一些局限性。

Plant condition assessment using remote sensing techniques have been associated with spectral vegetation indices such as the normalized difference vegetation index (NDVI). A change in NDVI values has been normally regarded as changes in vegetation amount or density. The spectral properties of plants, which are directly related to the health conditions, would also result in changes in spectral vegetation indices. Consequently, a lower vegetation index value may result from either lower density or nutrient stress, or a combination of the two. This would limit the use of vegetation indices as a monitoring tool. Bidirectional reflectance distribution function (BRDF) models treat plant density and optical properties differently and, therefore, can help to assess plant condition objectively. In this study, multiangular spectral reflectances were measured over two winter wheat canopies: one being under nitrogen stress and the other not. These multiangular measurements were then used in inversions of BRDF models to estimate the optical properties and the plant densities. The results show that it is feasible to obtain simultaneously the optical properties and plant densities and, therefore, it is possible to use BRDF models and multiangular remote sensing measurements to make diagnostic analysis of nitrogen-related plant conditions. The results also revealed some limitations of this approach such as inversion problems and computation time.