Multi Sensor-based Array Shape Direct Measurement Approach for Deep-sea Vertical Linear Array

A system based on vertical linear array is brought forward. The localization model is presented, and the localization principle of vertical linear array is discussed. With range, elevation angle induced from time-delay and the measurement of azimuth angle, three dimensional equation of state and equation of measurement have been established. The localization precise according to length of baseline and precise of time-delay is simulated and analyzed. According to the observability principle of nonlinear system, the observability qualifications of the system are given.

Estimation of modal wavenumbers is important for inference of geoacoustic properties and data-driven matched field processing in shallow water waveguides. This paper introduces a deep neural network called combining physical informed neural network (CPINN) for modal wavenumber estimation using a vertical linear array (VLA). Note that the sound field recorded by a VLA can be expressed as a linear superposition of finite modal depth functions, and the differential equations satisfied by the modal depth functions are related to the corresponding modal wavenumbers. CPINN can estimate the modal wavenumbers by introducing the proxies of the modal depth functions and constraining them to satisfy the corresponding differential equations. The performance of the CPINN is evaluated by simulated data in a noisy shallow water environment. Numerical results show that, when compared with the previous methods, CPINN does not need to know the exact horizontal distance between the sound source and the VLA. Moreover, CPINN can estimate the modal wavenumbers at the VLA position in the case where the range segment traversed by the source, i.e., the aperture in the range direction, is smaller than the maximum modal cycle distance and in a range-dependent waveguide.

Firstly, the elementary principle of passive estimation of target depth is studied, which is supported by underwater acoustic detection system of vertical linear array and is conducted in deep sea. Then, error sources of passive estimation of target depth are analysed theoretically from points of view of random error and deployment deviation of vertical linear array, and correlative formulae are deduced. After simulation experiments, it is concluded that how these error sources impact accuracy of passive estimation of target depth, which is the basis of further research for passive estimation of target depth and improvement of accuracy of passive estimation of target depth.

Natural gas hydrate (NGH) has the huge exploitation potential for clean energy in the current world energy pattern. Its total organic carbon storage is about twice the sum of carbon content of oil, gas, and coal and hence attracts the attention of the world. China has carried out some gas hydrate exploitation works and delineation of three gas hydrate deposits whose reserve scale is over 100 billion cubic meters, and the NGH resource is abundant. The NGH reservoir in the South China Sea is of low porosity and permeability, is unconsolidated, has poor cementation, and is easy to fragment in hydrate production. On the one hand, the condition of low porosity and permeability around the well would severely reduce the production effect; on the other hand, the hydrate decomposition would more easily bring wellbore instability caused by stratum stress change. Therefore, to achieve safe and efficient exploitation of NGH, proper reservoir reconstruct technology needs to be chosen for enhancing the reservoir's permeability and stability. This paper chose the Shenhu area of South China Sea as the research area, constructed the three-dimensional heterogeneous geological model of hydrate-bearing sediments which can be approximated realistically to depict, then used high-pressure jet grouting (HPJG) technology to reconstruct the hydrate reservoir, optimized the grouting hole direction, location, and spacing, and assessed the productivity increasing effect. The research results show the following: (a) Because of the higher hydrate saturation (SH) and lower permeability (k) around the well, the HPJG in the vertical direction was profitable for reservoir productivity. (b) Considering the heterogeneous SH and k in the horizontal direction, the HPJG in the front of the horizontal well was profitable for the reservoir productivity. (c) The HPJG spacing needs to be properly designed in combination with the absolute standard (VP), the relative standard (RGM), and the specific production index (J). (d) Under the conditions of this paper setting, the optimal HPJG reconstruction scheme is as follows: the HPJG in the vertical direction was arranged at the front of the horizontal well, and the spacing between the holes was 10 m. The productivity after reconstruction ranged up to 55.69% compared with before.

Association between multiphase seepage and exploitation of natural gas hydrate based on the Shenhu area of South China Sea

In shallow water, modal wavenumbers are useful for many applications. This paper presents an approach for wavenumber estimation of range-independent waveguide based on pressure and its finite difference (FD) data matrices built on the vertical linear array (VLA) data. The core of this method is that wavenumber information is expressed in the singular value decomposition (SVD) of the FD data matrix. Therefore, wavenumbers can be estimated directly by combining the SVDs of the pressure data matrix and FD data matrix. The method is validated on simulated data. The dependence of the proposed method on relevant parameters is discussed.

In view of exponential growth in data traffic demand, the wireless communications industry has aimed to increase the capacity of existing networks by 1000 times over the next 20 years. A combination of extreme cell densification, more bandwidth, and higher spectral efficiency is needed to support the data traffic requirements for fifth generation (5G) cellular communications. In this research, the potential improvements achieved by using three major 5G enabling technologies (i.e., small cells, millimeter-wave spectrum, and massive MIMO) in rural and urban environments are investigated. This work develops SPM and KA-based ray models to investigate the impact of geometrical parameters on terrain-based multiuser MIMO channel characteristic. Moreover, a new directional 3D channel model is developed for urban millimeter-wave (mmW) small cells. Path-loss, spatial correlation, coverage distance, and coherence length are studied in urban areas. Exploiting physical optics (PO) and geometric optics (GO) solutions, closed form expressions are derived for spatial correlation. Achievable spatial diversity is evaluated using horizontal and vertical linear arrays as well as planar 2D arrays. In another study, a versatile near-ground field prediction model is proposed to facilitate accurate wireless sensor network (WSN) simulations. Monte Carlo simulations are used to investigate the effects of antenna height, frequency of operation, polarization, and terrain dielectric and roughness properties on WSNs performance.

The conservation of marine tourism resources based on the public’s preference for non-use values is important to the sustainable development of marine tourism. The objectives of this article are to explore the willingness to pay (WTP) for the non-use values of marine tourism resources and how such WTP differs among types of marine tourism resources in China. A contingent valuation study was undertaken at three archipelagic tourism destinations: the Miaodao Archipelago, with beaches and maritime geological heritage (Yellow Sea and Bohai Sea areas); the Zhoushan Archipelago, with beaches and maritime culture (East China Sea area) and Sanya and nearby islands, with beaches and coral reefs (South China Sea area). Tourists’ WTP varies by resource type, among which the WTP for the above six subsamples ranged from ¥192.93 to ¥373.16, confirming the existence of the non-use values of marine tourism resources in China. These results not only provide references for determining priorities for protecting marine tourism resources but also suggest that policymakers can focus on the more attractive resources to raise conservation funds, thus promoting the realization of general conservation objectives. Furthermore, this article offers novel insights into the validity and reliability test of contingent valuation method (CVM) studies.

The fundamental and practical problem of passive localization in range and depth, of an acoustic underwater source is addressed, with application to an at-sea experiment. We propose and try a new matching method based on a metric called as Hausdorff distance as a cost-function to be minimized, in order to perform the localization inversion. The data set analyzed here was collected during the DGA campaign ALMA 2015, which took place in a shallow water environment of the southern coast of France. Acoustic data were measured over a 10m-high vertical linear array (VLA), composed of 64 hydrophones. The 2-D localization, in range and depth, is performed by matching the patterns of time difference of arrival (TDOA), between respectively observed and modeled sequences. Several variants of the Hausdorff Distance are applied, firstly separately in each single hydrophone, and then combined in order to improve the localization accuracy, reducing the ambiguity either is depth and in range. The performance is evaluated in terms of the localization accuracy of the proposed method, in a context of passive localization with a cooperative system considering a motionless target. Very satisfactory performance and accuracy are obtained.

This In order to reduce the difficulty of the practical application of the time reversal method (TRM), this paper proposed a new method of virtual TRM with a short vertical line array. The measurement field received by the short array is used to reconstruct an acoustic field of a virtual long vertical array. The method is mainly divided into three steps: Initially, using the modal decomposition to decompose the sound field received by the short vertical array into a modal function matrix and a modal coefficient vector. Furthermore, we obtain the estimated values of the modal coefficients of each order. In this paper, an iterative algorithm was used to obtain the modal coefficients of each order, and then the measured field of the long vertical line array is extended through the obtained modal coefficients. Finally, we use the extended vertical line array measurement field for time reversal processing. The results from the final computer simulation indicated that, due to the measurement field of the long vertical line after continuation contains more environmental information, the virtual time reverse processing method with the extended measurement field has superior focus positioning performance.

Past 140-year environmental record in the northern South China Sea: Evidence from coral skeletal trace metal variations

In this paper, the evolution of intraseasonal oscillation over the South China Sea and tropical western Pacific area and its effect to the summer rainfall in the southern China are studied based on the ECMWF data and TBB data) analyses. A very low-frequency waves exist in the tropics and play an important role in dominating intraseasonal oscillation and lead to special seasonal variation of intraseasonal oscillation over the South China Sea / tropical western Pacific area. The intraseasonal oscillation (convection) over the South China Sea and tropical western Pacific area is closely related to the summer rainfall (convection) in the southern China. Their relationship seems to be a seesaw feature, and this relationship resulting from the different pattern of convection in those two regions is caused by the differnt type of local meridional circulation.

Enhancing gas production in low-permeability natural gas hydrate reservoirs by the axial water jet slotting and grouting in vertical wellbores

Summary It has always been the focus of researchers to accurately identify gas hydrate location. Geophysical prospecting is a widely used method for gas hydrate exploration, which has high credibility, especially seismic exploration technology is most generally used. In our study, we analyze the different physical properties of gas hydrate and other minerals bearing in unconsolidated and high porosity marine sediments based on the effective medium theory. Thus, a new attribute is put forward to discriminate gas hydrate. The logging data at Dongsha area of South China Sea and Hydrate Ridge in Oregon continental margin are applied to validate this method. Our test results are basically in line with actual situation, which provides a new understanding in hydrate identification.

A fast identification method based on the typical geophysical differences between submarine shallow carbonates and hydrate bearing sediments in the northern South China Sea