GPS接收机天线装置定向标志线及平均相位中心参数的检测

本文讨论了GPS测量的重要误差来源之一——接收机天线相位中心漂移误差,研究了表征平均相位中心的基本参数及其检测和处理方法。如果用户设备进行了这种检测,并对观测成果作了相应的修正,目前大部分商品接收机在几十公里以内的短过测量中,精度可以提高到3 mm+2 ppm·d(d为边长,单位:km),同时解决了混合机组参加GPS网观测和处理的难题。     

National distribution of chemical concentrations in mussels and oysters in the USA

Since 1986 the NOAA National Status and Trends (NS&T) Program Mussel Watch has monitored concentrations of trace chemicals in the coastal United States by sampling mussels, oysters, and sediment. The sediment data have been used to define the status or geographic distribution of chemical concentrations (Daskalakis, K. D., & O'Connor, T. P. (1995). Distribution of chemical contamination in coastal and estuarine sediments. Marine Environmental Research 40, 381-398) and the molluscan data have provided an estimate of temporal trends (O'Connor, T. P. (1996). Trends in chemical concentrations in mussels and oysters collected along the US coast from 1986 to 1993. Marine Environmental Research 41,183-200, O'Connor, T. P. (1998). Mussel Watch results from 1986 to 1996. Marine Pollution Bulletin 37, 14-19). This paper centers on chemical concentrations in mollusks at 263 sites around the United States. It provides perspective on concentration ranges and on geographic distributions. For most organic chemicals and lead, concentrations vary in proportion to numbers of people living near a site. For elements, other than lead, high concentrations in mollusks can be due more to natural factors than to human activity. Concentrations of PAHs in tissues of mussels from urban areas are in a range reported to exert biological responses.     

Identification, definition and quantification of goods and services provided by marine biodiversity: implications for the ecosystem approach

This paper identifies and defines ecosystem goods and services provided by marine biodiversity. Case studies have been used to provide an insight into the practical issues associated with the assessment of marine ecosystem goods and services at specific locations. The aim of this research was to validate the definitions of goods and services, and to identify knowledge gaps and likely difficulties of quantifying the goods and services. A validated theoretical framework for the assessment of goods and services is detailed, and examples of the goods and services at a variety of case study areas are documented. These results will enable future assessments of marine ecosystem goods and services. It is concluded that the utilisation of this goods and services approach has the capacity to play a fundamental role in the Ecosystem Approach, by enabling the pressures and demands of society, the economy and the environment to be integrated into environmental management.     

精密水准测量成果的折光改正

精密水准测量是研究地壳垂直运动及其它一些地球物理现象的一个重要手段,而大气折光则为精密水准测量成果中一项主要的系统误差,数值远比一般预期的为大。影响对资料的分析,有必要找到适当的计算方法将它消去。本文在比较几种不同方案之后,推荐一种以安格斯·李潘公式为基础的改进方案,可以用来处理历史上的水准测量成果及未来的水准成果,其适用范围有待于进一步外业试验加以鉴定。     

切比雪夫多项式逼近在大地测量计算中的应用

本文根据切比雪夫多项式的定义和基本性质,导出求多项式函数最佳逼近的代数式,并运用这一结果解决了一些大地测量常用计算公式的最佳逼近问题。在同一电子计算机上利用这些数值逼近公式,其计算速度,以子午线孤长正反算为例可比相应的同精度的经典方法提高五倍至数十倍。     

Hydraulics of recirculating well pairs for ground water remediation

Recirculating well pairs are a proven means of implementing bioremediation and may also be useful for applying other in situ ground water remediation technologies. A bromide tracer test was performed to characterize the hydraulic performance of a recirculating well pair installed at Moffett Field, California. In particular, we estimate two important properties of the recirculating well pair: (1) the fraction of captured water that is recycled between the wells, and (2) the travel-time distribution of ground water in the induced zone of recirculation. We also develop theoretical estimates of these two properties and demonstrate they depend upon a dimensionless pumping rate, denoted xi. The bromide breakthrough curve predicted from theory agrees well with that determined experimentally at Moffett Field. The minimum travel time between the wells is denoted t(min). In theory, t(min) depends inversely on Q, the pumping rate in the recirculating wells, and is proportional to a2, the square of the distance between the wells. Both the experimental and theoretical travel-time distributions indicate that at least half the recirculating water travels between the wells along fast flowpaths (travel time < 2*t(min)). Therefore, when designing recirculating well pairs, engineers should ensure that t(min) will be sufficiently high to allow biologically mediated reactions (or other in situ remediation processes) sufficient time to proceed.     

带COGO的实时GPS测量及其功能扩展

实时ＧＰＳ测量作用ＧＰＳ测量的一种新技术,它拥有许多传统ＧＰＳ所不具备的优势,已经得到越来越多用户的认可。带ＣＯＧＯ功能的实时ＧＰＳ测量尽管问世半年有余,但此项功能仍然鲜为人知。作者研究结果表明此项技术值得广泛推广应用,同时指出其潜力其大,在待深入开发。文中给出的种种案例和操作步骤可供实进作业用户参考。     

GPS动力法定位的模型与估计问题

研究GPS在动力学环境下的网定位,对我国来说具有很大的吸引力。在GPS定位实践中,动力法及半动力法的轨道改进定位方式都具有广泛的应用,但前者概括了卫星定位中最一般的动力学问题。因此,本文归纳和建立了相应的动力法定位模型,包括轨道状态方程、地面测站的状态方程及观测方程。简要介绍了更能反映卫星定位问题统计和力学本质的最优滤波和最优控制的估计方法。最后给出了事后轨道估计的最佳平滑方程。