Estimation of incident photosynthetically active radiation from Moderate Resolution Imaging Spectrometer data
Estimation of incident photosynthetically active radiation from Moderate Resolution Imaging Spectrometer data
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DOI：
10.1029/2005jd006730
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发表时间：
2006-08-08
影响因子：
4.4
通讯作者：
Running, Steven
中科院分区：
文献类型：
--
作者：
Liang, Shunlin;Zheng, Tao;Running, Steven
[ 1]入射光合有效辐射（PAR）是几乎所有陆地生态系统模型所需的关键变量。不幸的是，目前的事件PAR产品估计从遥感数据在空间和时间分辨率是不够的碳循环建模和各种应用。在这项研究中，作者开发了一种新的方法的基础上查找表的方法来估计瞬时入射PAR的极轨中分辨率成像光谱仪（MODIS）数据。由于大气层顶（TOA）辐射取决于地面反射率和大气属性，在很大程度上决定了入射PAR，我们的第一步是估计表面反射率。该方法假设已知的气溶胶属性的观测与最小的蓝色反射从每个像素的时间窗口。然后将其反演的表面反射率插值以确定其他观测的表面反射率。第二步是通过将查找表中计算的TOA反射率与卫星观测的TOA值进行匹配来计算PAR。直接和漫射PAR分量以及总短波辐射都以完全相同的方式确定。还探讨了从一个或两个瞬时PAR值计算日平均PAR值。从七个FLUXNET站点的地面测量用于验证算法。结果表明，该方法可以产生合理的PAR产品在1 km分辨率，适合全球应用，但仍需要更多的定量验证活动。
[ 1] Incident photosynthetically active radiation ( PAR) is a key variable needed by almost all terrestrial ecosystem models. Unfortunately, the current incident PAR products estimated from remotely sensed data at spatial and temporal resolutions are not sufficient for carbon cycle modeling and various applications. In this study, the authors develop a new method based on the look-up table approach for estimating instantaneous incident PAR from the polar-orbiting Moderate Resolution Imaging Spectrometer (MODIS) data. Since the top-of-atmosphere (TOA) radiance depends on both surface reflectance and atmospheric properties that largely determine the incident PAR, our first step is to estimate surface reflectance. The approach assumes known aerosol properties for the observations with minimum blue reflectance from a temporal window of each pixel. Their inverted surface reflectance is then interpolated to determine the surface reflectance of other observations. The second step is to calculate PAR by matching the computed TOA reflectance from the look-up table with the TOA values of the satellite observations. Both the direct and diffuse PAR components, as well as the total shortwave radiation, are determined in exactly the same fashion. The calculation of a daily average PAR value from one or two instantaneous PAR values is also explored. Ground measurements from seven FLUXNET sites are used for validating the algorithm. The results indicate that this approach can produce reasonable PAR product at 1 km resolution and is suitable for global applications, although more quantitative validation activities are still needed.