Causes of systematic over‐ or underestimation of low streamflows by use of index‐streamgage approaches in the United States

Low‐flow characteristics can be estimated by multiple linear regressions or the index‐streamgage approach. The latter transfers streamflow information from a hydrologically similar, continuously gaged basin (‘index streamgage’) to one with a very limited streamflow record, but often results in biased estimates. The application of the index‐streamgage approach can be generalized into three steps: (1) selection of streamflow information of interest, (2) definition of hydrologic similarity and selection of index streamgage, and (3) application of an information‐transfer approach. Here, we explore the effects of (1) the range of streamflow values, (2) the areal density of streamgages, and (3) index‐streamgage selection criteria on the bias of three information‐transfer approaches on estimates of the 7‐day, 10‐year minimum streamflow (Q_{7, 10}). The three information‐transfer approaches considered are maintenance of variance extension, base‐flow correlation, and ratio of measured to concurrent gaged streamflow (Q‐ratio invariance). Our results for 1120 streamgages throughout the United States suggest that only a small portion of the total bias in estimated streamflow values is explained by the areal density of the streamgages and the hydrologic similarity between the two basins. However, restricting the range of streamflow values used in the index‐streamgage approach reduces the bias of estimated Q_{7, 10} values substantially. Importantly, estimated Q_{7, 10} values are heavily biased when the observed Q_{7, 10} values are near zero. Results of the analysis also showed that Q_{7, 10} estimates from two of the three index‐streamgage approaches have lower root‐mean‐square error values than estimates derived from multiple regressions for the large regions considered in this study. Published in 2011 by John Wiley & Sons, Ltd.     

Selenium and heavy metals content in some Mediterranean soils

The study of metal contents in industrial, agricultural or/and polluted soils compared with natural or unpolluted soils is currently necessary to obtain reference values and to assess soil contamination. Nonetheless, very few works published appear in international journals on elements like Se, Li and Sr in Spanish soils. This study determines the total levels of Se, Li, Sr, As, Cd, Co, Cr, Cu, Ni, Pb, V, Zn, Fe, Mn and Ba in 14 natural (unpolluted) soils (Gypsisols, Leptosols, Arenosols and Acrisols), 14 agricultural soils (Anthrosols, Fluvisols and Luvisols), and 4 industrial–urban affected-surface soil horizons (Anthrosols and Fluvisols) of Eastern Spain. The geochemical baseline concentrations (GBC) and reference values (RV) have been established, and the relationships among elements and also between soil properties and elemental concentrations have been analysed. The RV obtained in this study were (mg kg⁻¹): Se 2.68, Li 115, Sr 298, Cd 0.97, Co 35, Cr 217, Cu 46, Ni 50, Pb 137, V 120, Zn 246, Fe 124,472, Mn 2691, and Ba 743. The RV for Se and Li were used as a preliminary approach to assess soil contamination in Spanish soils. The results confirm human impact on Sr, As, Cd, Cr, Cu, Ni, Pb and Zn soil concentrations, but evidence no deviation from natural Se, Li, Co, V, Fe, Mn and Ba concentrations. The results obtained from the statistical analysis reveal significant correlations between some elements and clay and soil organic matter (SOM) contents, indicating that metal concentrations are controlled by soil composition. One particularly interesting finding is the high correlation coefficients obtained between SOM and Se, Cd, Cr, V, Fe, and Mn, and between clay and Cd, Zn, V, Fe and Mn. Once again, these facts confirm the role of SOM and clay minerals in soil functions and that soil is an ecosystem element responsible for maintaining environmental quality.     

机载PPP与动基线测量相对定位精度比较与分析

机载精密单点定位可测量单个载体的位置和速度,这一模式能够满足大多数应用的需求。但在某些特殊应用场合,比如:远洋编队航行、舰载飞机着舰、空中加油、飞船交会对接等,要求解决两个运动目标之间高精度的相对定位问题。文中通过采用PPP模式和动基线测量两种模式对两个运动目标的相对定位进行比较与分析。     

北斗导航卫星系统测距信号的精度分析

基于单测站和短基线实验的伪距相位差值 (Code-minus-phase Combination, CC)和多路径(Multipath, MP)两类组合观测值,对比分析了北斗（BD）和GPS测距信号质量,并检验了多路径误差对CC模糊度固定的影响。结果表明：BD GEO卫星(Geostationary Earth Orbit)的测距信号质量优于IGSO卫星(Inclined Geosynchronous Satellite Orbit),且两类测距信号的多路径误差分别包含长、短期的变化趋势。针对CC模糊度固定,当采用较长时间段（如本文中的600s）时,GPS L1/L2和BD B1/B2四个频段上的成功率均超90%;而对于快速模糊度固定（如仅采用120秒）,由于受强多路径误差影响,BD IGSO卫星的固定成功率最低,不超过50%。     

基于GAMIT的基线解算应用探究

GAMIT基线解算是GPS数据分析和处理的重要方法。本文主要介绍利用虚拟的linux系统,以GAMIT软件进行精确定位、基线解算的批处理过程。对GAMIT软件安装过程进行详细的介绍,并利用基站的数据信息进行基线解算,对结算结果进行分析并得出结论,其目的在于解算后能形成模块以进行不同点的精确定位。     

一种CORS基准站整周模糊度解算方法

利用CORS基准站坐标精确已知,根据各种双频线性组合观测方程,探讨了一种长基线整周模糊度快速解算方法,详细介绍了其解算原理,逐步推导了计算公式。最后通过CORS站实例,数据计算分析结果显示,其方法可快速、准确地确定整周模糊度值。     

GPS长基线数据处理方法分析

对长基线数据处理理论及流程进行了简要介绍,并用Bernese软件对试验数据采用不同的处理策略进行了长基线解算(大于500km),系统分析了观测时间长度、截止高度角和固定IGS站的个数,对于长基线坐标解算结果的影响,得出了一些有益的结论。     

使用GAMIT软件进行高精度GPS基线解算的方法与步骤

GAMIT是国际上常用的高精度GPS定位和定轨软件,在处理长基线和连续时段的静态定位方面有很多优点。本文结合具体实例,介绍GAMIT的安装、基本操作以及应用GAMIT进行高精度基线向量解算。     

基于GAMIT的IGS跟踪站网基线解算

简要阐述了应用GAMIT软件进行数据准备和数据处理的方法,在数据处理部分采用了批处理和分步处理两种方法,并结合国际地球力学服务组织(IGS)跟踪站部分站点所构成的控制网数据进行基线解算和精度分析。结果表明:GAMIT软件解算中长基线的相对精度能达到10-9量级,完全满足各级精度要求。     

GPS在卫星影像控制测量中的应用

随着遥感卫星影像分辨率的不断提高,利用卫星遥感影像进行地形图更新和测绘逐步成为一种高效率的测绘手段。利用GPS测量技术对卫星影像进行控制测量则是其中一项重要的基础工作。主要从GPS全野外控制测量作业方法、作业中的精度控制与分析及应注意的问题三个方面,就GPS测量技术在卫星影像控制测量中的应用作一介绍。