A Wavelet-Based Assessment of Topographic-Isostatic Reductions for GOCE Gravity Gradients
A Wavelet-Based Assessment of Topographic-Isostatic Reductions for GOCE Gravity Gradients
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DOI：
10.1007/s10712-014-9283-1
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发表时间：
2014-03
影响因子：
4.6
通讯作者：
T. Grombein;Xiaoguang Luo;K. Seitz;B. Heck
中科院分区：
文献类型：
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作者：
T. Grombein;Xiaoguang Luo;K. Seitz;B. Heck
欧空局卫星使命重力场和稳态海洋环流探测器（GOCE）的重力梯度测量结果包含重要的高频和中频信号成分，这主要是由地球地形和均衡质量的吸引力造成的。为了减轻由此产生的谐波向下延拓的数值不稳定性，所观察到的梯度可以使用移除-计算-恢复技术相对于地形均衡效应进行平滑。为此，地形均衡减少计算的正演模拟，采用先进的岩石-水-冰的方法。这种方法的基础是一个三层分解的地形与可变的密度值和修改后的Airy-Heiskanen均衡的概念，将深度模型的Mohorovičić不连续。此外，镶嵌体用于质量离散化，并布置在椭球参考表面上。为了评估GOCE重力梯度通过地形均衡还原的平滑程度，本文提出了一种基于小波的评估，并与空间域中的统计推断进行了比较。使用Morlet小波，连续小波变换应用到测量GOCE重力梯度之前和之后减少地形均衡信号。通过分析喜马拉雅地区的代表性数据集，就业的减少导致显着平滑的梯度。此外，在空间域中不可见的平滑效应可以在小波尺度图中检测到，使得基于小波的谱分析成为强大的工具。
Gravity gradient measurements from ESA’s satellite mission Gravity field and steady-state Ocean Circulation Explorer (GOCE) contain significant high- and mid-frequency signal components, which are primarily caused by the attraction of the Earth’s topographic and isostatic masses. In order to mitigate the resulting numerical instability of a harmonic downward continuation, the observed gradients can be smoothed with respect to topographic-isostatic effects using a remove–compute–restore technique. For this reason, topographic-isostatic reductions are calculated by forward modeling that employs the advanced Rock–Water–Ice methodology. The basis of this approach is a three-layer decomposition of the topography with variable density values and a modified Airy–Heiskanen isostatic concept incorporating a depth model of the Mohorovičić discontinuity. Moreover, tesseroid bodies are utilized for mass discretization and arranged on an ellipsoidal reference surface. To evaluate the degree of smoothing via topographic-isostatic reduction of GOCE gravity gradients, a wavelet-based assessment is presented in this paper and compared with statistical inferences in the space domain. Using the Morlet wavelet, continuous wavelet transforms are applied to measured GOCE gravity gradients before and after reducing topographic-isostatic signals. By analyzing a representative data set in the Himalayan region, an employment of the reductions leads to significantly smoothed gradients. In addition, smoothing effects that are invisible in the space domain can be detected in wavelet scalograms, making a wavelet-based spectral analysis a powerful tool.