Translation-invariant wavelet denoising of full-tensor gravity-gradiometer data

Denoising of full-tensor gravity-gradiometer data involves detailed information from field sources, especially the data mixed with high-frequency random noise. We present a denoising method based on the translation-invariant wavelet with mixed thresholding and adaptive threshold to remove the random noise and retain the data details. The novel mixed thresholding approach is devised to filter the random noise based on the energy distribution of the wavelet coefficients corresponding to the signal and random noise. The translation- invariant wavelet suppresses pseudo-Gibbs phenomena, and the mixed thresholding better separates the wavelet coefficients than traditional thresholding. Adaptive Bayesian threshold is used to process the wavelet coefficients according to the specific characteristics of the wavelet coefficients at each decomposition scale. A two-dimensional discrete wavelet transform is used to denoise gridded data for better computational efficiency. The results of denoising model and real data suggest that compared with Gaussian regional filter, the proposed method suppresses the white Gaussian noise and preserves the high-frequency information in gravity-gradiometer data. Satisfactory denoising is achieved with the translation-invariant wavelet.

A Preliminary Analysis of the Tomography Problems in Constructing Bridge and Dike-Road across Taiwan Strait

The construction of the bridge across Taiwan Strait has been studied for a long time and the feasibility study that has attracted attention among scientists and engineers on both sides of the Taiwan Strait[1-4].The key question is whether this bridge and dike-road across Taiwan Strait can be constructed with present technology under such complex geological conditions or not.The results of current researches indicate that the sea floor of the Strait is covered with a horizontal layer composed of both the Pleistocene and the Holocene sandstone and shale with a thickness of about 200~300m.The distance from Pingtan island to China's Xinzhu seashore is 124 km,which might be connected by 4-6 section bridges and 5-7 section of dike-roads,and serve as a best program of the route in the north Strait section.The NE offshore fault along the Fujian coast and that along the west coast of Taiwan,China are the major tectonic lines separated by several NW faults under the upper horizontal layer,these fault 3D feature may be detecting by geo-tomography technique,which can help to deal with the foundation of bridge and dike-road piers.It is judged that the construction of bridge and dike-road beginning from Pingtan to the China's Xinzhu seashore is worth recommendation.In the procedure of the construction of large and high height bridges,must consider the steel structural member be detected by industrial CT technology,and might detect the pier of bridge and dike-road which built by steel tube and reinforced concrete at dike-roads two side,in order to get the hard basement and getting the depth of the pier extend below the sea-floor by the seismic tomographic detection method.

长江口-杭州湾及其邻近海域沉积动力环境及物源分析

长江口—杭州湾及其邻近海域的物质输运与生态环境受海域沉积动力特征和物质来源影响。本文利用长江口—杭州湾及其邻近海域沉积物的粒度、铂族元素、稀土元素等分析资料,采用Pejrup M等提出的三角图分类法对长江口—杭州湾及其邻近海域沉积动力环境进行详细分析,将研究区分为8个沉积环境分区:二个强动力河口现代沉积区,二个近岸水团交汇作用区,一个陆架水团锋面区,二个残留沉积区,一个冷涡旋的现代沉积区。对比分析了各沉积动力环境区的粒度特征及其水动力条件,揭示各种水动力条件下的沉积特征,以及各种沉积环境的物源输入特征,为长江、黄河与东海间的物质输运和交换等的研究提供基础资料,有助于我们进一步理解物源、搬运介质、沉积条件等因素对海岸—陆架沉积体系的影响,为河口沉积学和生物地球化学等方面研究提供有用信息。