An effective filtering for GRACE time‐variable gravity: Fan filter
An effective filtering for GRACE time‐variable gravity: Fan filter
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DOI：
10.1029/2009gl039459
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发表时间：
2009-09
影响因子：
5.2
通讯作者：
Zizhan Zhang;Benjamin F. Chao;Yang Lu;Hou Tse Hsu
中科院分区：
文献类型：
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作者：
Zizhan Zhang;Benjamin F. Chao;Yang Lu;Hou Tse Hsu
空间低通滤波是处理GRACE时变重力（TVG）数据所必需的，否则会受到短波长噪声的困扰。在这里，我们设计了一种新的非各向同性滤波器，称为扇形滤波器：就球谐频谱而言，扇形滤波器只是一个二维双滤波器，由一个沿沿着阶的低通滤波器（与传统的各向同性滤波器相同）和一个沿沿着阶的低通滤波器组成，其在（n，m）平面上的轮廓投影是扇形的。它是确定性的，独立于先验或外部信息，其实施是直接的，结果是客观的。最重要的是，我们证明了这个简单的滤波器在类似条件下的同类滤波器中表现良好，特别是针对GRACE TVG解决方案中普遍存在的N-S条带噪声。我们证明了这与高斯权重在过滤器的长度，因此空间分辨率为300公里。我们还推导出风扇滤波器的标称幅度降低因子作为遵循Kaula规则的TVG信号的滤波器长度的函数。
Spatial low‐pass filtering is necessary for processing the GRACE time‐variable gravity (TVG) data which are otherwise plagued with short‐wavelength noises. Here we devise a new non‐isotropic filter, called the fan filter: In terms of the spherical harmonic spectrum, the fan filter is simply a 2‐D double filter consisting of a low‐pass along the degree n (the same as the conventional isotropic filter) simultaneously with a low‐pass along the order m, whose contour projection onto the (n, m) plane is fan‐shaped. It is deterministic and independent of a priori or external information, its implementation is straightforward, and the result is objective. Most importantly, we show that this simple filter performs well among its counterparts under similar conditions, in particular against the N‐S striping noises prevalent in the GRACE TVG solutions. We demonstrate this with Gaussian weights at filter length and hence spatial resolution as fine as 300 km. We also deduce the fan filter's nominal amplitude‐reduction factor as a function of the filter length for TVG signals that follow the Kaula rule.