A physically based approach to model LAI from MODIS 250 m data in a tropical region
A physically based approach to model LAI from MODIS 250 m data in a tropical region
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DOI：
10.1016/j.jag.2009.09.013
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发表时间：
2010-02
期刊：
影响因子：
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通讯作者：
P. Propastin;S. Erasmi
中科院分区：
文献类型：
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作者：
P. Propastin;S. Erasmi
根据250m分辨率中分辨率成像光谱仪(MOD250_LAI)的16天归一化植被指数(NDVI)数据，建立了叶面积指数(LAI)的时间序列。MOD250_LAI产品使用了一个物理辐射传输模型，该模型建立了LAI、植被覆盖率(FVC)和给定的地表反射率、景观照明条件和植被光学特性之间的关系。利用半球照相法对166个样地的LAI和FVC进行了现场测量，用于模型参数的校准和模型结果的验证。基于85个样地的地面测量树冠构型与Landsat ETM+波段光谱值之间的经验模型，在局部(像元)水平上计算了植被覆盖的光学特性，以光消光系数来概括。建立了一个综合了太阳天顶角和传感器视角的视角几何模型，模拟了光照条件对冠层光学特性的影响。结果表明，生成的MOD250_LAI数据集与地面实况信息和使用类似算法估计的30m分辨率的Landsat ETM+LAI具有很高的一致性。并将得到的MOD250_LAI与全球MODIS 1000m LAI产品(MOD15A2 LAI)进行比较。结果表明，两个LAI产品的空间分布和时间动态具有很好的一致性。然而，结果也表明，MOD15A2产品的年LAI幅度显著高于MOD250_LAI。这种较高的幅度是由于MOD15A2在叶片产量较低的季节阶段对热带雨林的叶面积指数有相当大的低估所致。
A time series of leaf area index (LAI) has been developed based on 16-day normalized difference vegetation index (NDVI) data from the Moderate Resolution Imaging Spectroradiometer (MODIS) at 250m resolution (MOD250_LAI). The MOD250_LAI product uses a physical radiative transfer model which establishes a relationship between LAI, fraction of vegetation cover (FVC) and given patterns of surface reflectance, view-illumination conditions and optical properties of vegetation. In situ measurements of LAI and FVC made at 166 plots using hemispherical photography served for calibration of model parameters and validation of modelling results. Optical properties of vegetation cover, summarized by the light extinction coefficient, were computed at the local (pixel) level based on empirical models between ground-measured tree crown architecture at 85 sampling plots and spectral values in Landsat ETM+ bands. Influence of view-illumination conditions on optical properties of canopy was simulated by a view angle geometry model incorporating the solar zenith angle and the sensor viewing angle. The results revealed high compatibility of the produced MOD250_LAI data set with ground truth information and the 30m resolution Landsat ETM+ LAI estimated using the similar algorithm. The produced MOD250_LAI was also compared with the global MODIS 1000-m LAI product (MOD15A2 LAI). Results show good consistency of the spatial distribution and temporal dynamics between the two LAI products. However, the results also showed that the annual LAI amplitude by the MOD15A2 product is significantly higher than by the MOD250_LAI. This higher amplitude is caused by a considerable underestimation of the tropical rainforest LAI by the MOD15A2 during the seasonal phases of low leaf production.