Locally adjusted cubic-spline capping for reconstructing seasonal trajectories of a satellite-derived surface parameter
Locally adjusted cubic-spline capping for reconstructing seasonal trajectories of a satellite-derived surface parameter
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DOI：
10.1109/tgrs.2006.872089
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发表时间：
2006-08-01
影响因子：
8.2
通讯作者：
Chen, Mingzhen
中科院分区：
文献类型：
--
作者：
Chen, Jing M.;Deng, Feng;Chen, Mingzhen
卫星衍生的植被指数及其产生的地表参数，如叶面积指数（LAI），不可避免地受到大气的影响。在地表参数的季节轨迹中，大气校正的误差通常很容易识别，因为大气效应通常会导致植被指数的不规则减少。本文提出了一种局部调整的三样条封顶（LACC）方法来筛选像素中受影响的数据点，并通过时间插值来替换它们。在LACC中，根据原始季节变化模式的局部曲率，自动确定控制拟合曲线局部平滑度的可变局部平滑参数。设计了一个迭代程序，通过逐步用拟合值替换异常低值来产生季节性封顶曲线。与现有的基于谐波的方法相比，该方法有两个优点，即：1)三次样条可以灵活地模拟大范围的季节变化模式；2)可变的局部平滑参数允许拟合的封顶曲线模拟不同季节的快速或缓慢变化模式。封顶曲线在数学上也是可微分的，可用于进一步的应用。通过对中国几种覆盖类型的实例研究和对2001年中国中分辨率成像光谱仪LAI图像的处理，验证了该方法的有效性。
Satellite-derived vegetation indices and their resulting surface parameters, such as the leaf area index (LAI), are inevitably affected by the atmosphere. Errors in the atmospheric corrections can often be easily identified in a seasonal trajectory of a surface parameter because the atmospheric effect generally causes erratic reductions in vegetation indices. A locally adjusted cubic-spline capping (LACC) method is developed here to screen affected data points in a pixel and to replace them through temporal interpolation. In LACC, a variable local smoothing parameter, which controls the local smoothness of the fitted curve, is automatically determined according to the local curvature of the original seasonal variation pattern. An iteration procedure is designed to produce a seasonal capping curve by progressively replacing abnormally low values with fitted values. This method has two advantages over existing methods based on harmonics, namely: 1) cubic splines are flexible for simulating a wide range of seasonal variation patterns and 2) a variable local smoothing parameter allows the fitted capping curve to mimic either rapid or slow variation patterns in various seasons. The capping curve is also mathematically differentiable for further applications. The effectiveness of this method is demonstrated through case studies for several cover types in China and processing a series of Moderate Resolution Imaging Spectroradiometer LAI images of China in 2001.