Calibrating the GOCE accelerations with star sensor data and a global gravity field model

A reliable and accurate gradiometer calibration is essential for the scientific return of the gravity field and steady-state ocean circulation explorer (GOCE) mission. This paper describes a new method for external calibration of the GOCE gradiometer accelerations. A global gravity field model in combination with star sensor quaternions is used to compute reference differential accelerations, which may be used to estimate various combinations of gradiometer scale factors, internal gradiometer misalignments and misalignments between star sensor and gradiometer. In many aspects, the new method is complementary to the GOCE in-flight calibration. In contrast to the in-flight calibration, which requires a satellite-shaking phase, the new method uses data from the nominal measurement phases. The results of a simulation study show that gradiometer scale factors can be estimated on a weekly basis with accuracies better than 2 × 10⁻³ for the ultrasensitive and 10⁻² for the less sensitive axes, which is compatible with the requirements of the gravity gradient error. Based on a 58-day data set, scale factors are found that can reduce the errors of the in-flight-calibrated measurements. The elements of the complete inverse calibration matrix, representing both the internal gradiometer misalignments and scale factors, can be estimated with accuracies in general better than 10⁻³.     

Non-stationary covariance function modelling in 2D least-squares collocation

Standard least-squares collocation (LSC) assumes 2D stationarity and 3D isotropy, and relies on a covariance function to account for spatial dependence in the observed data. However, the assumption that the spatial dependence is constant throughout the region of interest may sometimes be violated. Assuming a stationary covariance structure can result in over-smoothing of, e.g., the gravity field in mountains and under-smoothing in great plains. We introduce the kernel convolution method from spatial statistics for non-stationary covariance structures, and demonstrate its advantage for dealing with non-stationarity in geodetic data. We then compared stationary and non- stationary covariance functions in 2D LSC to the empirical example of gravity anomaly interpolation near the Darling Fault, Western Australia, where the field is anisotropic and non-stationary. The results with non-stationary covariance functions are better than standard LSC in terms of formal errors and cross-validation against data not used in the interpolation, demonstrating that the use of non-stationary covariance functions can improve upon standard (stationary) LSC.     

面向流媒体传输的空间数据变化累积模型

将流媒体技术引入到以矢量数据为主的网络GIS传输中,其关键是建立逐级精细化的多层次表达模型,并在服务器端数据预组织上建立线性索引结构。本研究针对该目标建立一种矢量数据多重表达的新模型,即变化累积模型,认为尺度空间中从粗到细的数据表达过程是一些"变化"的累积,"变化"表现为两个连续尺度表达间的差别,通过"变化"元素的逐渐增加或减少来实现渐进传输。基于该模型对面状数据渐进式传输进行研究,将多边形分级剖分为一系列凸壳或外接矩形的基础上建立变化累积模型,通过剖分元素的组合完成渐进式流媒体传输。     

基于能量守恒的星间距离变率与地球重力场频谱关系的建立与分析(英文)

The spectral relationship between range-rate measurements and the gravity potential for low-low satellite-to-satellite tracking mission was established based on the energy conservation theory. Then the performances of satellite separation, the orbital altitude, and the accuracy of range-rate measurements in recovering the earth’s gravity field were simulated and analyzed by this method. Finally, the cumulative geoid errors of the reference mode were obtained by using the configuration parameters of the GRAC...     

基于ERMapper软件的QuickBird卫星影像处理实践

采用卫星遥感方法制作的数字正射影像是获取基础空间信息最快速、高效的手段,利用高精度卫星遥感成图,处理速度快、工艺简便、图像清晰,而且精度达到成图要求。本文介绍了以高分辨率的QuickBird卫星影像为研究对象,利用ERMapper图像处理系统进行图像的几何校正、全色与多光谱数据融合方法与过程。     

Ocean coast effect on magnetotelluric data: a case study from Kachchh, India

The effects of the ocean coast on magnetotelluric (MT) data have been studied and results are described in this article. MT soundings from various sites along coastal plains of Kachchh were acquired where volcanic rocks overlie Mesozoic sediments having potential resource prospects. The region of our study lies in the proximity of Gulf of Kachchh and Arabian Sea. This article describes the effects the presence of a conductive body on the acquired MT data. With the help of synthetic MT modelling and induction arrows we demonstrate the influence of shallow conductive body on the MT data. The modelling results when compared to the field observations show that much of the high frequencies are unaffected by the coast, however low frequencies of the data do seem to be distorted by onshore–offshore resistivity contrasts. The least affect on high frequencies can be attributed to very shallow water depth as well as to the fact that the onshore–offshore resistivity contrasts are not large enough to influence the high frequency data badly. The results presented here report for the first time the effect of the coast on the analysis on MT data from Kachchh. Due to several academic as well as industrial onshore–offshore MT experiments presently being carried out to explore its hydrocarbon potential, our results have an important bearing on designing and acquisition of future MT surveys in this region.     

Numerical calculation of free-surface potential flow around a ship using the modified Rankine source panel method

A modified Rankine source panel method is presented for solving a linearized free-surface flow problem with respect to the double-body potential. The method of solution is based on the distribution of Rankine sources on the hull as well as its image and on the free surface. An iterative algorithm is used for determining the free surface and wave resistance using upstream finite difference operator. A verification of numerical modeling is made using the Wigley hull and the validity of the computer program is examined by comparing the details of wave profiles and wave making resistance with Series 60 model.     

Numerical flow and performance analysis of a water-jet axial flow pump

The purpose of the present study is to investigate the performance and three-dimensional flow fields in a water-jet pump. TASCflow is employed to simulate the rotator-stator coupling flow field. A standard k-ε turbulence model combined with standard wall functions is used. In order to investigate the effect of a rear stator on flow fields, the flows in two water-jet pumps with and without a rear stator are studied. Computational fluid dynamics (CFD)-predicted overall performances are in good agreement with the experimental results. Then the flow fields, such as the pressure distribution on the blade surfaces, and the axial and tangential velocity distribution, especially the radial loading distribution, are investigated at different flow rates. In addition, the effects of a rear stator and different spacings between the rotor and the stator on the overall performance and the flow fields of the water-jet pump are also investigated.     

大黄鱼病原副溶血弧菌拮抗菌的筛选

用点种法从大黄鱼肠道优势菌群中筛选出104株病原性副溶血弧菌的拮抗菌,进一步研究拮抗效果最好的11株拮抗菌的抗菌谱和生长曲线,其中NAC平板上筛选的4株拮抗菌的抗菌范围较广,锰营养琼脂培养基上筛选的3株拮抗菌具有生长优势。用BIOLOG板测定了抗菌谱较广、有一定生长优势3株拮抗菌(R22,Y58和J312)的碳源利用情况,结果表明,3株拮抗菌的碳源谱都比较广,都能利用糖类、有机酸和氨基酸等,而且与鱼类营养的竞争较小。16S rRNA基因同源性分析的结果显示与R22,Y58,J312同源性达99%以上的菌株分别来自弧菌属、芽孢杆菌属和假单胞菌属。进一步对R22,J312和Y58三株拮抗菌进行生化鉴定,结果显示R22为溶藻弧菌,J312为荧光假单胞菌,但Y58的种属未能得到确认。所得到的3株拮抗菌R22,Y58,J312在拮抗病原菌、抗菌谱、生长特性和营养利用等方面都初步满足益生菌的筛选条件,有待进一步检测其安全性和实用效果以便能够成为能实用的益生菌。     

Surface current field and seasonal variability in the Kuroshio and adjacent regions derived from satellite-tracked drifter data

The muhiyear averaged surface current field and seasonal variability in the Kuroshio and adjacent regions are studied. The data used are trajectories and （1/4） ° latitude by （1/4） ° longitude mean currents derived from 323 Argos drifters deployed by Chinese institutions and world ocean circulation experiment from 1979 to 2003. The results show that the Kuroshio surface path adapts well to the western boundary topography and exhibits six great turnings. The branching occurs frequently near anticyclonic turnings rather than near cyclonic ones. In the Luzon Strait, the surface water intrusion into the South China Sea occurs only in fall and winter. The Kuroshio surface path east of Taiwan, China appears nearly as straight lines in summer, fall, and winter, when anticyclonic eddies coexist on its right side; while the path may cyclonically turning in spring when no eddy exists. The Kuroshio intrusion northeast of Taiwan often occurs in fall and winter, but not in summer. The running direction, width and velocity of the middle segment of the Kuroshio surface currents in the East China Sea vary seasonally. The northward intrusion of the Kuroshio surface water southwest of Kyushu occurs in spring and fall, but not in summer. The northmost position of the Kuroshio surface path southwest of Kyushu occurs in fall, but never goes beyond 31 °N. The northward surface current east of the Ryukyu Islands exists only along Okinawa-Amami Islands from spring to fall. In particular, it appears as an arm of an anti- cyclonic eddy in fall.