Residual errors in altimetry data detected by combinations of single- and dual-satellite crossovers

 The single- and dual-satellite crossover (SSC and DSC) residuals between and among Geosat, TOPEX/Poseidon (T/P), and ERS 1 or 2 have been used for various purposes, applied in geodesy for gravity field accuracy assessments and determination as well as in oceanography. The theory is presented and various examples are given of certain combinations of SSC and DSC that test for residual altimetry data errors, mostly of non-gravitational origin, of the order of a few centimeters. There are four types of basic DSCs and 12 independent combinations of them in pairs which have been found useful in the present work. These are defined in terms of the `mean' and `variable' components of a satellite's geopotential orbit error from Rosborough's 1st-order analytical theory. The remaining small errors, after all altimeter data corrections are applied and the relative offset of coordinate frames between altimetry missions removed, are statistically evaluated by means of the Student distribution. The remaining signal of `non-gravitational' origin can in some cases be attributed to the main ocean currents which were not accounted for among the media or sea-surface corrections. In future, they may be resolved by a long-term global circulation model. Experience with two current models, neither of which are found either to cover the most critical missions (Geosat & TOPEX/Poseidon) or to have the accuracy and resolution necessary to account for the strongest anomalies found across them, is described. In other cases, the residual signal is due to errors in tides, altimeter delay corrections or El Ni?o. (Various examples of these are also presented.) Tests of the combinations of the JGM 3-based DSC residuals show that overall the long-term data now available are well suited for a gravity field inversion refining JGM 3 for low- and resonant-order geopotential harmonics whose signatures are clearly seen in the basic DSC and SSC sets. Received: 15 January 1999 / Accepted: 9 September 1999     

基于数学优化方法的全站仪设站研究

文中提出了一种数学优化方法对大射电望远镜(Large Radio Telescope)LT5 m模型中用于跟踪测量的全站仪的站点坐标进行修正.目的是为了提高全站仪的设站精度,从而进一步提高其跟踪测量精度.实验表明,应用该方法使得全站仪的测量精度由原来的最大误差5 mm降低至最大误差为1 mm.达到了预期的目的.     

奎-玛两河流域冰雹灾害时空分布规律及特征分析

利用奎—玛两河流域7个气象站和33个农业点(兵团团场,农场)1970—2005年4—9月的成灾冰雹资料,对其发生的天气气候规律、时空分布特征,本区域内分布情况及差异、移动路径、冰雹直径、强度等方面进行分析,旨在为该区域成灾降雹天气的分析预报提供背景依据。     

Variation of singularity of earthquake-size distribution with respect to tectonic regime

Frequency-size relation of earthquakes in a region can be approximated by the Gutenberg-Richter law(GR). This power-law model involves two parameters: a-value measuring seismic activity or earthquake productivity, and b-value describing the relation between frequencies of small and large earthquakes.The spatial and temporal variations of these two parameters, especially the b-value, have been substantially investigated. For example, it has been shown that b-value depends inversely on differential stress. The b-value has also been utilized as earthquake precursor in large earthquake prediction.However, the physical meaning and properties of b-value including its value range still remain as an open fundamental question. We explore the property of b-value from frequency-size GR model in a new form which relates average energy release and probability of large earthquakes. Based on this new form of GR relation the b-value can be related to the singularity index(1-2/3 b) of fractal energy-probability power-law model. This model as applied to the global database of earthquakes with size M ≥ 5 from 1964 to 2015 indicates a systematic increase of singularity from earthquakes occurring on mid-ocean ridges, to those in subduction zones and in collision zones.     

基于最大顺序统计量的P波初动极性自动读取方法的小震震源机制反演及在云南小江地区的应用研究

地震P波震相到时与初动极性的精确读取是地震资料分析处理的重要步骤之一.本研究采用了一种新的高精度自动确定地震波P波震相到时与初动极性的概率分布的方法(POI方法,后同),在此基础上研究开发了一套自动化小震震源机制解的反演流程,并将其应用在云南小江断裂带周边区域的小震震源机制和构造应力场反演中.得到的震源机制与应力场反演结果与前人的研究一致,且与区域GPS观测结果和构造背景吻合度较好,显示该方法具有良好的应用前景,为高效分析密集台阵地震观测资料,开展小震震源参数测量与区域应力场反演提供了新的研究思路和技术手段.     

Multivariate analysis and geochemical investigations of groundwater in a semi-arid region,case of superficial aquifer in Ghriss Basin,Northwest Algeria

This study aims to investigate the hydrochemical characteristics of shallow aquifer in a semi-arid region situated in northwest Algeria, and to understand the major factors governing groundwater quality. The study area is suffering from recurring droughts, groundwater resource over-exploitation and groundwater quality degradation. The approach used is a combination of traditional hydrochemical analysis methods of multivariate statistical techniques, principal component analysis (PCA), and ratios of major ions, based on the data derived from 33 groundwater samples collected in February 2014. Results show that groundwater in the study area are highly mineralized and collectively has a high concentration of chloride (as Cl^?). The dominant water types are Na-Cl (27%), Mg-HCO₃ (24%) and Mg-Cl (24%). According to the (PCA) approach, salinization is the main process that controls the hydrochemical variability. The PCA analysis reveal the impact of anthropogenic factor especially the agricultural activities on the groundwater quality. The PCA highlighted two types of recharge: Superficial recharge from effective rainfall and excess irrigation water distinguished by the presence of nitrate and lateral recharge or vertical leakage from carbonate formations marked by the omnipresence of HCO₃^?. Additionally, three categories of samples were identified: (1) samples characterized by good water quality and receiving notable recharge from carbonate formations; (2) samples impacted by the natural salinization process; and (3) samples contaminated by anthropogenic activities. The major natural processes influencing water chemistry are the weathering of carbonate and silicate rocks, dissolution of evaporite as halite, evaporation and cation exchange. The study results can provide the basis for local decision makers to ensure the sustainable management of groundwater and the safety of drinking water.     

岩溶区桩基力学特性分析及桩型优化设计研究

设计人员在岩溶区进行市政、铁路等重荷载建筑作业时,往往采用桩基础以满足上部结构对地基土的承载力需求。桩基设计亦按照岩溶区桩基技术规范,在完整基岩满足限值的前提下,验算基础承载力并选定基础设计参数,进而指导施工。分析我国各地区岩溶勘探现状,基岩裂隙的不均匀性造成岩溶发育的不规律性,导致基岩岩溶分布与埋深无特定关系。故按照既有经验,机械执行设计规范,以完整基岩作为桩长控制的唯一因素,不可避免地造成经济浪费。通过采用土工布等限定成桩边界,建立桩基受力模型,得出岩溶段桩体可提供的最大摩阻力,并将其作为桩体力学平衡组成因素。最终通过岩溶率统计,估算潜在摩阻力值,从而在满足承载力需求的情况下,调整设计桩长及勘探深度,进而制定特定地区设计原则,优化成桩工艺、节约工程造价。     

Automated metric characterization of urban structure using building decomposition from very high resolution imagery

Classification approaches for urban areas are mostly of qualitative and semantic nature. They produce interpreted classes similar to those from land cover and land use classifications. As a complement to those classes, quantitative measures directly derived from the image could lead to a metric characterization of the urban area. While these metrics lack of qualitative interpretation they are able to provide objective measure of the urban structures.Such quantitative measures are especially important in rapidly growing cities since, beside of the growth in area, they can provide structural information for specific areas and detect changes. Rustenburg, which serves as test area for the present study, is amongst the fastest growing cities in South Africa. It reveals a heterogeneous face of housing and building structures reflecting social and/or economic differences often linked to the spatial distribution of industrial and local mining sites. Up to date coverage with aerial photographs is provided by aerial surveys in regular intervals. Also recent satellite systems provide imagery with suitable resolution. Using such set of very high resolution images a fully automated algorithm has been developed which outputs metric classes by systematically combining important measures of building structure. The measurements are gained by decomposition of buildings directly from the imagery and by using methods from mathematical morphology. The decomposed building objects serve as basis for the computation of grid statistics. Finally a systematic combination of the single features leads to combined metrical classes.For the dominant urban structures verification results indicate an overall accuracy of at least 80% on the single feature level and 70% for the combined classes.     

ArcGIS在地理国情普查图设计中的应用研究

当前,地理国情普查在我国全面展开,数据采集工作即将完成。未来,普查成果的应用及展示将是地理国情普查的主要工作。本文论述了利用ArcGIS软件,设计、制作地理国情普查图的实现过程,为地理国情普查成果的图形化展示提供了新的思路和方法。     

Development and comparison of aerial photograph aided visualization pipelines for LiDAR datasets

Light Detection and Ranging (LiDAR) technology generates dense and precise three-dimensional datasets in the form of point clouds. Conventional methods of mapping with airborne LiDAR datasets deal with the process of classification or feature specific segmentation. These processes have been observed to be time-consuming and unfit to handle in scenarios where topographic information is required in a small amount of time. Thus there is a requirement of developing methods which process the data and reconstruct the scene in a small amount of time. This paper presents several pipelines for visualizing LiDAR datasets without going through classification and compares them using statistical methods to rank these processes in the order of depth and feature perception. To make the comparison more meaningful, a manually classified and computer-aided design (CAD) reconstructed dataset is also included in the list of compared methods. Results show that a heuristic-based method, previously developed by the authors perform almost equivalent to the manually classified and reconstructed dataset, for the purposes of visualization. This paper makes some distinct contributions as: (1) gives a heuristics-based visualization pipeline for LiDAR datasets, and (2) presents an experimental design supported by statistical analysis to compare different pipelines.