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首页> 外文期刊>IEEE Transactions on Geoscience and Remote Sensing >Locally adjusted cubic-spline capping for reconstructing seasonal trajectories of a satellite-derived surface parameter
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Locally adjusted cubic-spline capping for reconstructing seasonal trajectories of a satellite-derived surface parameter

机译：局部调整的三次样条上限用于重建卫星衍生的表面参数的季节性轨迹

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摘要

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.
机译：卫星衍生的植被指数及其产生的表面参数，例如叶面积指数（LAI），不可避免地受到大气的影响。大气校正中的误差通常可以很容易地在表面参数的季节性轨迹中识别出来，因为大气效应通常会导致植被指数的下降。此处开发了一种局部调整的三次样条加盖（LACC）方法，以筛选像素中受影响的数据点并通过时间插值替换它们。在LACC中，根据原始季节变化模式的局部曲率自动确定一个变量局部平滑参数，该参数控制拟合曲线的局部平滑度。迭代过程旨在通过用拟合值逐渐替换异常低的值来生成季节性上限曲线。与基于谐波的现有方法相比，该方法有两个优点，即：1）三次样条可以灵活地模拟各种季节性变化模式； 2）可变的局部平滑参数允许拟合的上限曲线模拟快速变化模式或缓慢变化模式在各个季节。封顶曲线在数学上也可以区分以用于进一步的应用。通过对中国几种封面类型进行案例研究并在2001年处理了一系列中国的中分辨率成像光谱仪LAI图像，证明了该方法的有效性。

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