范文经典 时间:2020-03-23


Unit 9 Basic Statistical Analysis of Random Errors (随机误差的统计学基本分析)

Random errors are those variables that remain after mistakes are detected and eliminated and all systematic errors have been removed or corrected from the measured values.【eliminate】后,并且所有系统误差被从测量值中移除或修正后,保留下的那些变量【variable变量、变化n.】)

They are beyond the control of the observer.So the random errors are errors the occurrence of which does not follow a deterministic pattern.确定性的】模式【pattern】而发生的误差)

In mathematical statistics, they are considered as stochastic variables, and despite their irregular behavior, the study of random errors in any well-conducted measuring process or experiment has indicated that random errors follow the following empirical rules:【mathematical statistics】中,它们被当成随机变量【stochastic variable】,尽管它们的行为无规律,在任一正确的【well-conducted原意为品行端正的,这里指测量实验和活动是无误的】测量活动和实验中,对的随机误差的研究显示【indicate】随机误差遵循以下经验法则【empirical

⑴A random error will not exceed a certain amount.(随即误差不会超过一个确定的值)

⑵Positive and negative random errors may occur at the same frequency.(正负误差出现的频率相同)

⑶Errors that are small in magnitude are more likely to occur than those that are larger in magnitude.比数值大的误差出现可能性大【be likely to 可能】)

⑷The mean of random errors tends to zero as the sample size tends to infinite.随机误差的平均值趋近于0)

In mathematical statistics, random errors follow statistical behavioral laws such as the laws of probability.【statistical】行为【behavioral行为的】规律,如概率法则)

A characteristic theoretical pattern of error distribution occurs upon analysis of a large number of repeated measurements of a quantity, which conform to normal or Gaussian distribution.观测分析【analysisn.】中的误差分布的一个特征理论模式,遵照

【conform to遵照】正态或高斯分布)【在对一个量进行大量重复观测分析后,得到一个误差分布的理论特征——正态或高斯分布】

The plot of error sizes versus probabilities would approach a smooth curve of the characteristic bell-shape.与……相对】概率的关系图,接近一条光滑的特有的【characteristic特有的】钟形曲线。)

This curve is known as the normal error distribution curve.


It is also called the probability density function of a normal random variable.【probability density】函数)

It is important to notice that the total area of the vertical bars for each plot equals 1.This is true no matter the value of n (the number of single combined measurements), and thus the area under the smooth normal error distribution curve is equal to 1.量数目【独立观测数】)是多少,在光滑的误差正态分布曲线下的面积都是1。)

If an event has a probability of 1, it is certain to occur, and therefore the area under the curve represents the sum of all the probabilities of the occurrence of errors.线下方的面积代表了所有误差发生的概率。)

A number of properties that relate a random variable and its probability density function are useful in our understanding of its behavior.具【property】与随机变量和它的概率密度函数有关,有助于我们理解它的行为)

Mean and standard deviation are two most popular statistical properties of a random variable.


Generally, a random variable which is normally distributed with a mean and standard deviation can be written in symbol form as N(μ,σ2).地,一个通常由平均值和标准偏差描述的随机变量可以用符号

【symbol】表示为N(μ,σ2They can be explained as follows.

Mean: The most commonly used measure of central tendency is the mean of a set of data (a sample).【measure】就是一系列数据(一个样本)的平均值)

The concept of mean refers to the most probable value of the random variable.It is also called by any of the several terms—expectation, expected value, mean or average. 平均值或平均值)

The mean is defined as Where xi are the observations, n is the sample size, or total number of observations in the sample, and x is the mean which is also called most probable value (MPV).测值的总数,x是平均值,经常被称为最或是值(MPV)

The MPV is the closest approximation to the true value that can be easily achieved from a set of data.【approximation】,可以很容易由一系列数据得到。)

It can be shown that the arithmetic mean of a set of independent observations is an unbiased estimate of the meanμof the population.以看出【It can be shown that】一系列独立【independent】观测值的算数平均值【arithmetic mean】是一个样本【population】的期望值μ的无偏估计【unbiased estimate】。)

Standard deviation is a numerical value indicating the amount of variation about a central value.指示【indicate】相对于中值的偏离)

In order to appreciate the concept upon which indices【index的复数】 of precision devolve one must consider a measure that takes into account all the values in a set of data.(考虑一系列数据的所有值精度指标 必需顾及一个量,这个量考虑到【takes into account考虑】一组【a set of】数据的所有值)

Such a measure is the deviation from the mean x of each observed value xi i.e. (xi- x), and the mean of the squares of the deviations may be used, and this is called the varianceσ2,的离差【deviation】,也就是,(xi- x),离差的平方的平均值被采用,称之为方差σ2)

Where μ is the mean (expectation) of the population.体【样本】的平均值(期望值)。)


Uuit1 What is Geomatics? (什么是测绘学)

Geomatics Defined(测绘学定义) Where does the word Geomatics come from?(Geomatics-测绘或地球空间信息学,这个名词 是怎么来的呢?)

GEODESY+GEOINFORMATICS=GEOMATICS or GEO- for earth and – MATICS for mathematical or GEO- for Geoscience and -MATICS for informatics. (大地测量学+地理信息 学=GEOMATICS 测绘学或者 geo 代表地球,matics 代表数学,或者 geo 代表地球科学, matics 代表信息学)It has been said that geomatics is many things to many people.(据说测 绘学这个词对不同的人有不同的理解) The term geomatics emerged first in Canada and as an academic discipline; it has been introduced worldwide in a number of institutes of higher education during the past few years, mostly by renaming what was previously called “geodesy” or “surveying”, and by adding a number of computer scienceand/or GIS-oriented courses.(这 个术语作为一个学科第一次形成于加 拿大;在过去的几年里被全世界的许多高等教育研究机构所熟知,通常是以前的“大地测量 学”或“测量学”在引入了许多计算机科学和 GIS 方向的课程后重新命 名的。 )

Now the term includes the traditional surveying definition along with surveying steadily increased importance with the development of new technologies and the growing demand for a variety of spatially related types of information, particularly in measuring and monitoring our environment.

(随着新技术的发展和不断增长的对空间关系的信息类型的需求,尤其是在测 量和监测我们的环境方面 , 现在, 传统测量学定义连同 日益增长的测量的重要性一起包含在这个术语里了。) Increasingly critical are areas of expanding populations,

appreciating land values, dwindling natural resources, and the continuing stressing of the quality of our land, water and air from human activities. (日益增长的危机来自人口扩张,地价上涨,资源紧缩【紧张】 ,还有由于 人类活动引起的土地、水、空气质量的持续的压力 As such, geomatics bridges wide arcs from the geosciences through various engineering sciences and computer sciences to spatial planning, land

development and the environmental sciences.(这样,测绘学在地球科学,各种工程学,计算机科 学, 空间规划, 土地开发和环境科学相互之间架起了广泛的桥梁。 ) Now the word geomatics has been adopted by several international bodies including the International Standards Organization(ISO),so it is here to stay.(现在 geomatics 这个词已经被包括 ISO在内的数个国际机构 所采用, 因此它就这样被普遍接受

The term “surveyor” is traditionally used to collectively describe those engaged in the above activities. (surveyor 这个词按惯例用来总指 (这换成 “总 称” 较好) 那些从事上述活动的人。 ) More explicit job descriptions such as Land Surveyor, Engineering Surveyor or Hydrographic Surveyor for example, are commonly used by practitioners to more clearly describe and market their specialized expertise. (更具

体的工作如土地测量员、工程测量员和水道测量员,被业内人士用来更准确的描述他们的专门技术。 The term geomatics is a recent creation to convey the truecollective and scientific nature of these related activities and has the flexibility to allow for theincorporation of future technological developments in these fields.(geomatics 这个术语是个新 词,表达了实体集合和它们相关联的活动的自然科学,并使这些领域的未来技术发展的结合成为可能。)

Adoption of the term also allows a coherent marketing of the profession to industry and schools on a worldwide basis. (这个术语的采用同时也在全世界范围里为行业里和学校建立了一个一致的专业市场) As a result, both course and awardtitles in the traditional Land Surveying sector at many of the world’ s leading universities are being changed to “Degree in Geomatics”. (结果,世界上许多一流大学的传统的测量专业的无论是课程还是授予资格都改为“测绘学位”的了) This does not suggest the demise of the term “surveyor” and graduates will still practice as land

surveyors or photogammertrists, etc. as appropriate to their specialization.(这并不意味着“surveyor”这个词的消亡,测绘毕业生还将从事适合他们专业的土地测量员、摄影测量员及其他的工作) In the last decade, there has been dramatic development and growth in the use of hardware and software solutions to both measure and process geo-spatial data.(在过去的十年中,在应用硬件和软件的方法来测量和处理地球空间数据工作时有着戏剧性的发展和增长)This has created and will continue to create new areas of application, with associated job opportunities for suitably

qualified graduates. (创造并将继续创造新的应用领域,并为合适的、合格的毕业生提供相关的工作。) As a result, the role of the “surveyor” is expanding beyond traditional areas of practice, as described above, into new areas of opportunity.(结果是,“surveyor”的角色大大超越传统实践领域――如前面所述的领域,进入到新的领域。) In addition, recent advances in the technology of data collection and

processing have blurred the boundaries of practice and activity between what were previously regarded as related but separate areas.(另外,最近的数据采集和处理技术的发展模糊了以前被认为有联系却分离的领域的界限) Such developments are forecast to continue and willcreate new career paths for graduates whose education and training is broadly based and of a high academic standard.(可以预见,这种发展继续并将为涉猎广泛、学识一流的毕业生创造新的事业。) To enable graduatesto take full advantage of these developments, significant changes in education and training are required.(为了使毕业生能充分利用这些发展,教育和训练的重大改革成为必需的) Academic and professional institutions are also responding, in part, by adopting the term geomatics both as a course and as an award title. (学院的和专业的机构也作出反应,部分地,采用术语“geomatics”作为一门课程和一项授予资格)。

A working definition of geomatics, which reflects current thinking and predicted

change, is:(测绘学的一个现在使用的反映了当前的思想和对未来的预期的定义是:)

The science and technology of acquiring, storing, processing, managing, analyzing and presenting geographically referenced information(geo-spatial data ).(获取、处理、存储,分析和上呈地理参考信息(地理空间信息)的科学和技术。) This broad term applies both to science and technology, and mapping, geodesy, satellite positioning, photogrammetry, remote sensing, geographic information systems(GIS), land management ,computer systems, environmental visualization and computer graphics.(这个广泛的术语应用于科学和技术,以及制图、大地测量学、卫星定位、摄影测量学、遥感、地理信息系统、土地管理、计算机系统、环境可视化和计算机制图等领域) Several terms such as “geomatics” , “geomatic engineering,” and “geoinformatics” are now in common use pertaining to activities generally concerned with geographic information.(现在一些术语如“测绘学”,“测绘工程”“地学信息学”和共同应用于某些活动中―――专属于通常涉及地理信息的活动。) These terms have been adopted primarily to represent the general approach that geographic information is collected, managed, and applied. (这些术语起初被采用用来表示地理信息的采集、管理和应用的总体的方法。) Along with land surveying,

photogrammetry, remote sensing, and cartography, GIS is an important component of geomatics. (连同土地测量学,摄影测量学,遥感和制图学一起,GIS 也是测绘学中重要的一个组成部分。)

Branches of Geomatics(测绘学分支)

Data acquisition techniques include field surveying, global positioning system(GPS), satellite positioning, and remotely sensed imagery obtained through aerial

photography and satellite imagery. (数据获取技术包括普通野外测量,GPS 测量,卫星定位和遥感图像获取,通过航空摄影和卫星成像) It also includes the acquisition of database material scanned from older maps and plans and data collected by

related agencies.(它还包括数据库资料的获取――通过扫描就有地图和设计图,还有有关机构收集的数据。) Data management and process are handled through the use of computer programs for engineering design, digital photogrammetry, image analysis, relational data base management, and geographic information systems

(GIS).(通过计算机程序,数据管理和处理应用于工程设计,数字摄影测量,图像分析,相关资料库的管理和 GIS。) Data plotting(presentation) is handled through the use of mapping and other illustrative computer programs; the presentations are displayed on computer screens(where interactive editing can occur) and are output on paper from digital plotting devices.(数据成图是通过制图和其他直观的计算机程序进行的;其表达显示在计算机屏幕上(交互式编辑处理),也可以通过数字绘图仪输出到纸上。) Once the positions and attributes of geographicentities have been digitized and stored in computer memory, they are available for use by a wide

variety of users.(一旦地理实体的位置和属性被数字化并被存储进计算机存储器,就可以有效的为广泛的各种的使用者所用) Through the use of modern information technology(IT), geomatics brings together professionals in the following disciplines: surveying, mapping, remote sensing, land registration, civil and marine engineering, forestry,

agriculture, planning and development, geology, geographical sciences,

infrastructuremanagement, navigation, environmental and natural resources

monitoring, and computerscience.(通过现代信息技术,测绘学将以下学科的专业人员整合到一起:测量学、制图学、遥感、国土注册、土木工程和海洋工程,林业,农业,决策与发展,地质学,地理科学,基础设施管理,导航,环境与自然资源监测和计算机科学。)

Other Definitions of Geomatics (测绘学的其他定义)

As defined by the Canadian Institute of Geomatics in their quarterly journal “Geomatica”: Geomatics is a field of activities which, using a systemic approach, integrates all the means used to acquire and manage spatial data required as part of scientific, administrative, legal and technical operations involved in the process of the production and management of spatial information. (加拿大测量学会在他们的季刊“地球空间信息学”中这样定义:测绘学是利用系统的方法,为生产和处理科学的,行政的,法律的和技术的业务所需的空间信息,将所有获取和管理空间信息的方法整合在一起的活动领域的一部分

The definition of Geomatics is evolving. A working definition might be “ the art, science and technologies related to the management of geographically-referenced information.” Geomatics includes a wide range of activities, from the acquisition and analysis of site-specific spatial data in engineering and development surveys to the application of GIS and remote sensing technologies in environmental management. It includes cadastral surveying, hydrographic surveying, and ocean mapping, and it plays an important role in land administration and land use management .(测绘学定义在发展。现行的一个定义是“涉及工艺、科学和技术的地理信息的处理”。测绘学或地球空间信息学包括一个广泛的生产活动――从工程学和发展了的测量学领域中特殊点的空间数据的获取和分析到 GIS 和遥感技术在环境管理中的应用。它包括地籍测量、水道测量和海图测量,在土地管理和土地使用中扮演重要的角色。)

Geomatics is the modern scientific term referring to the integrated approach of measurement, analysis, management, storage and display of the descriptions and location of Earthbased data, often termed spatial data. These data come from many sources, including earth orbiting satellites, air and sea-borne sensors and ground based instruments. It is processed and manipulated with state-of-the-art information technology using computer software and hardware. It has applications in all disciplines which depend on spatial data, including environmental studies, planning, engineering, navigation, geology and geophysics, oceanography, land development and land ownership and tourism. It is thus fundamental to all the geoscience

disciplines which use spatially related data .(测绘学是一个现代科学术语,用以表示测量、分析、管理,存储和显示基于地球信息,经常被称为空间数据 数据的描述和位置的集成方法。这些数据来自各种数据源,包括地球轨道卫星,空载和舰载传感器及地面仪器。利用计算机软件和硬件,借助现代信息技术。它的应用覆盖所有依赖空间数据的学科,包括环境研究,规划,工程学,导航,地质和地球物理学,海洋学,土地开发,土地经营和旅游学。它因而成为所有使用空间数据地球科学学科的基础。)

[from the School of Geomatic Engineering, Univ. of New South Wales](摘自新南威尔士大学测绘工程学院)

Geomatics is concerned with the measurement, representation, analysis, management, retrieval and display of spatial data concerning both the Earths physical features and the built environment. The principal disciplines embraced by Geomatics include the mapping sciences, land management, geographic information systems, environmental visualization, geodesy, photogrammetry, remote sensing and surveying. (测绘学是测量、表示,分析,处理,重获和显示关于地球物理特征和环境的空间数据的科学。其包括的主要学科有制图学,土地管理,GIS,环境可视化,大地测量学,摄影测量学,遥感和测量学。) [from the Dept. of Geomatics at Univ. of Melbourne](摘自墨尔本大学测绘学系

Geomatics comprises the science, engineering, and art involved in collecting and managing geographically-referenced information. Geographical information plays an important role in activities such as environmental monitoring, management of land and marine resources, and real estate transactions. (测绘学包括自然科学,工程学和工艺或学;对地理信息的收集与管理。地理信息在环境监测,陆地和海洋资源管理,以及房地产交易中扮演重要角色。 [from the Dept. of Geodesy and Geomatics Engineering at UNB](摘自加拿大纽布朗斯维克大学测量与大地测量学系)

The science of Geomatics is concerned with the measurement, representation, analysis,management, retrieval and display of spatial information describing both the Earth’s physicalfeatures and the built environment. Geomatics includes disciplines such as : Surveying, Geodesy,Remote Sensing & Photogrammetry, Cartography, Geographic Information Systems, Global Positioning Systems. (测绘学测量,表示,分析,管理,重获和显示空间信息,用来描述地球物理特征和环境。测绘学包括的学科有:测量学,大地测量学,遥感和摄影测量学,制图学,GIS,GPS ) [from the Dept. of Sruveying and Spatial Information Science at the Univ. of Tasmania] (摘自塔斯马尼亚大学,测量与空间信息科学系)

Unit 2 Geodetic Surveying and Plane Surveying(大地测量与平面测量) Surveying has been traditionally defined as the art and science of determining the position of natural and artificial features on, above or below the earth’s surface; and representing this information in analog form as a contoured map, paper plan or chart, or as figures in report tables, or in digital form as a three dimensional mathematical model stored in the computer. (测量传统定义为确定地表、地下和地上的自然与人工地貌特征;并使之按比例测绘成地形图、平面图或图表,或形成报告图表,或以数字形式形成三维立体数学模型存储进计算机。) As such, the surveyor/geodesist dealt with the physical and mathematical aspect of measurement. (同样的,测量员/大地测量学家处理的就是测量出的物理的和数学的特征) The accurate determination and monumentation of points on the surface of the Earth is therefore seen as the major task. (因此精确确定并标定地表点位便成为测量的主要任务)



Unit 20 Understan ding the GPS(认识 GPS)

What Is GPS?(什么是 GPS)

The global Positioning System (GPS) operated by the U .S. Department OF Defense (DOD)is a satellite-based system that can be used to locate positions anywhere on the earth(.全球定位系统(GPS),由美国国防部管理,是一个基于人造卫星的系统,可以用来在全球任何地方定位)GPS provides continuous (24 hours/day), real-time, 3-dimensional positioning, navigation and timing worldwide.(GPS 提供全世界范围内的全天候,实时,三维坐标,导航和授时的功能。)Any person with a GPS receiver can access the system, and it can be used for anyapplication that requires location coordinates.(任何拥有一台 GPS 接收机的人都可以使用这套系统,可以应用于任何需要位置坐标的工作中)The GPS system consists of three segments: ⑴ the space segment: the GPS satellitesthemselves, ⑵the control segment, operated by the U .S. military, and ⑶the user segment,which includes both military and civilian users and their GPS equipments(.GPS 由三个部分组成:⑴太空部分:GPS 卫星自己,⑵地面控制部分,由美国军方控制,⑶用户部分,包括军方和民用用户和他们的装备。)Space Segment: The GPS Constellation(太空部分: GPS 星座)The first GPS satellite was launched by the U .S. Air Force in early 1978.(第一颗 GPS 卫星由美国空军在 1978 年的早些时候发射的)There are now 24 satellites orbiting the earth at an altitude of about 10,900 miles.(现在有24 颗卫星在绕地球大约 10900 英里的高度运行)The high altitude insures that the satellite orbits are stable, precise and predictable, and that the satellites’ motion through space is not affected by atmospheric drag.(这么高的高度确保了卫星轨道是稳定、精确和可知的,并且确保了卫星穿过太空的运行不受到大气阻力的影响)There are four satellites in each of 6 orbital planes.(6 个轨道平面中每个有 4 颗卫星。)Each plane is inclined 55 degrees relative to the equator, which means that satellites crosstie equator tilted at a 55 degrees angle.(每个平面相对于赤道面倾斜55 度,这就意味着这些卫星以 55 度角穿过赤道)The system is designed to maintain full operational capability even if two of the 24satellites fail.(这套系统被设计成即使 24 颗卫星的 2 颗故障也能维持全工作能力)These 24 satellites make up a full GPS constellation.(这 24 颗卫星组成了一个完整 的GPS 星座)The GPS satellites are powered primarily by sun-seeking solar panels, with nicad batteries providing secondary power.(GPS 卫星主要由太阳定向太阳能电池板提供动力,镍镉蓄电池提供备用动力)Each GPS satellite has four atomic clocks on board, only one of which is in use at a time. These highly accurate atomic clocks enable GPS to provide the most accurate timing system that exists. (每一个 GPS 卫星有四个原子钟,某一时刻只有一台在使用。这些高精度原子钟能够使 GPS 提供最准确的时间系统)Control Segment: U.S. DOD Monitoring(控制部分:美国国防部监控)The U .S. Department Of Defense maintains a master control station at Falcon Air Force Base in Colorado Springs.(美国国防部维持了一个主控站,在科罗拉多斯普林斯的佛肯空军基地)There are four other monitor stations located in Hawaii, Ascension Island, Diego Garcia and Kwajalein.(还有 4 个监控站座落在夏威夷、阿松森岛、迭哥加西亚岛、卡瓦加兰岛)The DOD stations measure the satellite orbits precisely.(DOD 站精确测量卫星轨道)Any discrepancies between predicted orbits and actual orbits are transmitted back to the satellites.(任何预报轨道和实际轨道之间的偏差被传回卫星。)The satellites can then broadcast these corrections, along with the other position and timing data, so that a GPS receiver on the earth can precisely establish the location of each satellite it is tracking.(然后卫星可以广播这些改正值 ——连同位置和时间数据一起,以便地球上的 GPS 接收机可以精确确定它所跟踪的每个卫星的位置)User Segment: Military and Civilian GPS Users (用户部分:军方和民用 GPS 用户)The U .S. military uses GPS for navigation, reconnaissance, and missile guidance systems.(美国军方把 GPS 用在导航、侦察和导弹制导系统上Civilian use of GPS developed at the same time as military uses were being established, and has expanded far beyond original expectations.(GPS 的民用在军用建立起之时就发展起来了,并且已经发展的远远超过起初的期望)There are civilian applications for GPS in almost every field, from surveying to transportation to natural resource management to agriculture.(GPS 的民用用途几乎 用在每个领域,从测量到交通到自然资源管理到农业)Most civilian uses of GPS, however, fall into one of three categories: navigation, positioning and timing.(然而, GPS 的大部分民


How Does GPS Work?( GPS 如何工作)

A GPS receiver calculates its position by a technique called satellite ranging, which involves measuring the distance between the GPS receiver and the GPS satellites it is tracking.(GPS 接收机利用一项被称为卫星测距的技术,计算它自己的位置,涉及到 GPS 接收机到它所跟踪的 GPS 卫星的距离测量)The range (the range a receiver calculates is actually a pseudorange, or an estimate orange rather than a true range) or distance is measured as elapsed transit time.(距离(接收机测的距离实际上是伪距,或者说是距离估值,而不是真实距离)是用传播时间来测的)The position of each satellite is known, and the satellites transmit their positions as part of the “ messages” they send via radio waves.(每个卫星的位置已知,并且卫星将它们的位置作为它们用无线电波发出的“讯文”的一部分传送出去)The GPS receiver on the ground is the unknown point, and must compute its position based on the information it receives from the satellites.(地面 GPS 接收机是未知点,必需基于它从卫星收到的这些信息计算它的位置。)The first step in measuring the distance between the GPS receiver and a satellite requires measuring the time it takes for the signal to travel from the satellite to the receiver.(测量GPS 接收机和卫星的第一步,要求测出从卫星到接收机的信号传播时间。)Once the receiver knows how much time has elapsed, the travel time of the signal multiplies the speed of light (because the satellite signals travel at the speed of light, approximately 186,000 miles per second) to compute the distance.(一旦接收机知道用了多少时间,用信号的传播时间乘上光速(因为卫星信号以光速传播,大约186,000 英里每秒)来计算距离。)Distance measurements to four satellites are required to compute a 3-dimensional (latitude, longitude and altitude) position.(计算一个三维(纬度、精度和高程)位置需要4 颗卫星的距离值)

In order to measure the travel time of the satellite signal, the receiver has to know when the signal left the satellite and when the signal reached the receiver.(为了测出卫星信号的传播时间,接收机需要知道信号是什么时候离开卫星的和什么时候到达接收机的)Knowing when the signal reaches the receiver is easy, the GPS receiver just “ checks” its internal clock when the signal arrives to see what time it is(.确定信号到达接收机的时间容易,GPS 接收机只需在信号到达时“检查”自己内置的钟,看看是什么时间)But how does it “know” when the signal left the satellite?(但是怎样“知道”信号何时离开卫星的呢?)All GPS receivers are synchronized with the satellites so they generate the same digital code at the same time.(所有 GPS 接收机与卫星是同步的,因此它们在同一时间产生同样的信号码)When the GPS receiver receives a code from a satellite, it can look back in its memory bank and “remember” when it emitted the same code(.当 GPS 接收机收到一个从卫星来的码时,它可以在它的内存条中回忆并“记起”它发出的相同码)This little “ trick” allows the GPS receiver to determine when the signal left the satellite.(这个小小的“技巧”使得 GPS 接收机能够确定信号是何时离开卫星的)Once the receiver has the distance measurements, it’s basically a problem of geometry(.一旦接收机测出了距离,基本上就只有几何上的问题了)If it “ knows” where the four satellites are, and how far it is from each satellite, it can compute its location through trilateration. Here’s an illustration of how it works.(如果知道了 4 颗卫星的位置,距每颗卫星的距离,就可以通过三边测量来计算它的位置。这里有个例子说明它如何工作的)The GPS receiver “ locks on” to one satellite and calculates the range to be 12,000 miles.(GPS 接收机“锁定”一颗卫星并计算出距离为 12,000 英里)This fact helps narrow the receiver location down, but it only tells us that we are somewhere on a sphere which is centered on the satellite and has a 12,000 mile radius.(这把接收机的位置限定下来,但是它只能告诉我们在一个以这个卫星为中心,半径 12,000 英里的球面上)Many of the locations on that sphere are not on earth, but out in space.(这个球面的许多位置不在地球上,而在太空中)Now,consider that the receiver picks up a signal from a second satellite and calculates the range between the receiver and the satellite to be 10,000 miles.(现在,考虑这个接收机从第二颗卫星获得一个信号,计算出接收机到这颗卫星的距离是 10,000英里)That means we are also somewhere on a sphere with a 10,000 mile radius with the second satellite at the center.(这就意味着我们也在一个以第二颗卫星为中心、半径 10,000 英里的球面上的某处)We must, therefore, be somewhere where these two spheres intersect.(因此,我们肯定在这两个球面相交的某处。)When the two spheres intersect, a circle is formed, so we must be somewhere on that circle.(当这两个球面相交时,一个圆圈形成了,因此我们肯定在这个圆圈的某处)If the receiver picks up another satellite, says at 11,000 miles

away, another sphere is formed, and there are only two points where the three spheres intersect.(如果接收机“拾取”了另一个卫星,比方说11,000 英里以外,另一个球面形成了,三个球面相交只有两个交点)Usually the receiver can discard one of the last two points because it is nowhere near the earth.(通常接收机可以丢弃最后这两点中的一个点,因为它离地球差的 远)So, we’re left with one point which is the location of the GPS receiver.In practice, a fourth measurement is needed to correct for clock error(.这样我们留下一个点,它是 GPS 接收机的位置。在实际当中,需要第四个观测值来修正时间误差)

Uuit21 Understanding the GPS (II) 认识 GPS(II)

GPS Error Sources (GPS 误差来源 )There are many sources of possible errors that will degrade the accuracy of position computed by a GPS receiver.(有许多或然误差来源, 这种误差 会降低GPS 接收机计算的位置的准确度)The travel time of GPS satellite signals can be altered by atmospheric effects; when a GPS signal passes through the ionosphere and troposphere it is refracted, causing the speed of the signal to be different from the speed of a GPS signal in space.(GPS 卫星信号的传播时间会因大气影响而改变;当 GPS 信号穿过电离层和对流层时会发生折射,因为信号速度与在太空中信号的速度不同。)Sunspot activity also causes interference with GPS signals(.太阳黑子活动也对 GPS 信号产生干扰)Another source of error is measurement noise, or distortion of the signal caused by electrical interference or errors inherent in the GPS receiver itself.(另一个误差源是测量噪声,或者是由于电干扰或 GPS 接收机自己固有的误差引起的信号失真)Errors in the ephemeris data (the information about satellite orbits) will also cause errors in computed positions, because the satellites weren’ t really where the GPS receiver “thought” they were (based on the information it received) when it computed the positions.(星历数据(关于卫星轨道的信息)误差也会引起位置的误差,因为当计算位置时,卫星不真正地在接收机“认为”它们在的地方(基于它接受的信息所知道))Small variations in the atomic clocks (clock drift) on board the satellites can translate to large position errors; a clock error of 1 nanosecond translates to 1 foot or 0 .3 meters user error on the ground.(卫星原子钟内的很小的变化(钟漂)能转化成很大的位置误差;一纳秒的钟差能造成 1 英尺或 0.3 米的地面用户误差)Multi path effects arise when signals transmitted from the satellites bounce off a reflective surface before getting to the receiver antenna.(当从卫星发射的信号在到达接收机天线 之前,被一个反射面反射时,多路径效应出现了)When this happens, the receiver gets the signal in straight line path as well as delayed path(multiple paths). The effect is similar to a ghost or double image on a TV set(.当这种情况发生时,接收机接收直线路径来的信号,也接收延迟路线(多路径)来的信号。其效果与电视的重影或重像类似)How to Reduce GPS Errors(如何减小 GPS 的误差)You’ve probably heard people talk about getting 2 to 5 meters accuracy with a GPS receiver, or even centimeter or millimeter accuracy(.你可能听说过有人说 GPS 接收机可以达到 2 到 5 米的准确度,甚至是厘米或毫米级精度)Is there a way to cancel out the errors and get satisfied accuracy?(有方法低偿误差并获得满意的精度吗?) The answer is yes, but the level of accuracy depends on the type of equipment you are using.(回答是肯定的,但是准确度的级别依赖于你使用的装备的类型)The following discussion describes a technique used to achieve 2 to 5 meters accuracy using mapping (resource) grade receivers.(下面的讨论描述了一种用于绘图(资源)级接收机的技术,能够获得 2 到 5 米的准确度)Some mapping grade receivers are even capable of sub-meter accuracy, but the increased accuracy comes at a price.(一些绘图级的接收机甚至能够达亚米级精度,但是精度的提高是以很高代价带来的Survey grade receivers are the most accurate, capable of centimeter or even millimeter accuracy, depending on the equipment, but they use more advanced techniques to achieve this level of accuracy and, naturally, are more expensive.(测地级接收机最精确,凭装备能够达到厘米甚至是毫米级精度,但是它们是使用更先进的技术才得到这样的精度水平,自然地,就更昂贵。)Recreational grade receivers usually can receive real-time differential corrections, but they cannot store a file that can be differentially corrected using post-processing methods.(休闲级的接收机通常可以接收实时差分改正,但是它们不能存储文件,以便可以用后处理方法差分改正。) Differential Correction(差分改正)

Differential correction is a method used to reduce the effects of selective available (SA) and other sources of GPS positioning error (differential correction cannot correct for multipath or receiver error; it

counteracts only the errors that are common to both reference and roving receivers).(差分改正是一种用来减小 选择可用性政策(SA)影响和其它 GPS 定位误差源 的方法(差分改正不能修正多路径效应或接收机误差;它只能抵消基准接收机和流动接收机所共有的误差)It requires, in addition to your “ roving” GPS receiver, a GPS receiver on the ground in a known location to act as a static reference point.(这需要——除了你的“流动”GPS 接收机之外 —— 一个 GPS 接收机在地面上一个已知的位置担当参考点)

This type of setup is often called a GPS base station. Since the base station “ knows” where it is, it can compute the errors in its position calculations (in reality, it computes timing errors) and apply them to any number of roving receivers in the same general area.(这种设备经常被称为 GPS 基准站。由于基准站“知道”在哪儿,它就可以计算它自己的

位置误差(实际上,它是计算 定时误差),并将它们应用于将……应用于】许多同一区域的流动接收机)This requires that the base and rover receivers “ see” the same set of satellites at the same

time.(这需要基准接收机和流动接收机同时“看到”相同一批卫星)The base station, depending upon how it is configured, can correct roving GPS receiver data in one (or both) of two ways.(基准站,依照如何配置,可以用两种中的一种方法(或同时用两种)对 GPS 流动接收机的数据进行修正)⑴in the first method, called real-time differential correction or real-time differential GPS (DGPS), the base station transmits (usually via radio link) error correction messages to other GPS receivers in the local area.(第一种方法,称为实时差分改正或实时差分 GPS(DGPS),基准站发射(通常经由无线电联系)误差改正信息到其它当地的 GPS 接收机)In this case, the positions you read on your GPS receiver while you are out collecting data are the corrected positions.(这样,当你外出收集数据时在你的 GPS 接收机上读出的位置就是改正后的位置。)⑵ the second method, called post-processed differential correction, is performed on a computer after the roving receiver data are collected.(第二种方法,称为后处理差分改正,在流动站数据收集完后经由计算机完成的)While you are out in the field collecting data, the positions you read on your roving GPS receiver are uncorrected.(当你在野外收集数据时,你在 GPS 流动接收机上读出的位置是未经修正的)It is not until you take the rover files back to the office and process them using differential correction software and data from the base station file, that you get corrected positions(.直到你把流动站文件带回办公室并利用差分改正软件和基准站的文件数据进行处理,你才能得到改后位置)The base station file contains information about the timing errors.(基准站文件包括同步误差信息)This information allows the differential correction software to apply error corrections to the roving receiver file during processing(.这种信息可以在处理时使差分改正软件把误差改正施于流动接收机文件上。)Since the base and rover receivers have to “see” the same set of satellites at the same time, the base file has to start before the rover file starts, and end after the rover file ends (a base station is normally set up to track all satellites in view, insuring that it will “ see” at least the four satellites that the roving receiver is using to compute positions)(.由于基准站接收机和流动站接收机必需同时 “看到”同一组卫星,基准站文件必需开始于流动站文件之前,结束于流动站文件之后(基准站通常设置为跟踪所有视野内的卫星,以保证至少“看到”流动站接收机用来计算位置的 4 颗卫星))Post-processed differential correction, then, requires both base and rover receivers that are capable of collecting and storing files.(后处理差分改正,要求基准站接收机和流动接收机都能收集和存储文件。)Most recreational grade receivers cannot collect and store files that can be differentially corrected.(多数休闲级接收机不能收集和存储可以用来差分改正的文件)How Accurate Is GPS?( GPS 准确度如何?) The accuracy that can be achieved using GPS depends on the type of equipment used, the time of observation, the positions of the satellites being used to compute positions, the model and the software you used.(使用 GPS 可以达到的准确度依赖于使用装置的类型、观测时间、用来计算位置的卫星的位置、你所使用的模式和软件)In general, recreational and mapping grade receivers using C/A code without differential correction are accurate to between 30 and 100 meters.(大体上讲,使用 C/A 码没有差分改正的休闲和绘图级接收机精度在 30 到 100 米之间。)Many people using recreational grade receivers don’ t realize they cannot get highly accurate readings using them autonomously (without differential correction)(.许多用休闲类接收机的人没有意识到他们直接使用(没有差分改正)它们不能取得高精度的读数。)Unfortunately ,some manufacturers’ ads are misleading and only confuse the

situation.(不幸地是,有些厂商的广告误导并混淆了这种情况)They claim 30 meters accuracy, which actually means 30 meters GEP (circular error probable).(他们宣称有 30 米的精度,实际上那意味着 30 米的 GEP(圆概然误差)This means that positions will be within 30 meters 50 percent of the time.(这意味着这个位置有 50%的机会在 30 米内)There is really no way to tell whether you are within 30 meters or within 100 or more meters of the true position.(实在不能说你是在真实位置的 30 米内或者 100 米内或着更多米内)

Most mapping and recreational grade receivers with differential correction can provide from about 2 to 5 meters accuracy(.大多数差分改正的测图和休闲类接收机可以提供 2到 5 米的准确度)Some receivers use what is called “ carrier-smoothed code” to increase the accuracy of the C/A code.(有些接收机利用被称为“载波平滑码”来增加 C/A 码的精度)This involves measuring the distance from the receiver to the satellites by counting the number of waves that carry the C/A code signal.(这涉及利用计算承载 C/A 码信号的载波数来测量从接收机到卫星的距离)These receivers can achieve 10 cm to 1 meter accuracy with differential correction.(这些接收机可以利用差分改正达到 10cm 到 1 米的精度)Dual frequency survey grade receivers using more advanced network survey techniques can achieve centimeter to millimeter accuracy(.双频测量型接收机利用更先进的联合测量技术,可以达到厘米到毫米的精度)

Unit22 Competition in Space Orbit(太空轨道上的竞争)

Around the world, countries are mobilizing to build independent satellite navigation networks, troubled that the Global Positioning System (GPS) is run by the US military and controlled by the US government.(环绕世界,顾虑到 GPS 由美国军方运作并受到美国政府的控制,许多国家都努力建立独立卫星导航网)On March 7, 1995 was announced the Russian Federation Government’s decree “On executing works in use of the GLONASS system for the sake of civil users”(.在 1995.3.7,俄罗斯联邦政府宣布一项法令“GLONASS 系统民用计划”)

It was also reported on “ 21st century” , 2001 that the European Union says the US couldn’ t guarantee the reliability and availability of the GPS civilian signal, as United States national security needs could potentially outweigh any other needs.(2001 年“二十一世纪”也报道说,欧盟说美国不能保证GPS 民码的可靠性和有效性,由于美国国家安全需要潜在地超过了其它任何需要)“Europe cannot accept reliance on a military system which has the possibility of being cut off,” said Rene Oosterlinck, head of the navigation department at the European Space Agency ,fairly summing up the emotions GPS brings about abroad.(“欧洲不能接受依赖一个有可能被切断的军方系统”,Rene Oosterlinck说道,欧洲航空局导航部主任,清楚的概括了 GPS 对国外产生的情绪。)

In response, Europe will spend billions assembling a civil satellite system called Galileo ,scheduled to be operation by 2008.(作为反应,欧洲将花费数十亿装配一个民用卫星系统称为“Galileo”,预期在 2008 年运转

For the benefit of students to get some knowledge on the competition in space orbit, brief introduction to GLONASS, GALILEO and BEIDOU is provided as follows.(为了使学生们得到一些太空轨道上的竞争的知识,下面提供了关于 GLONASS,GALILEO 和北斗的简要介绍)


The Russian Federation’s GLObal Navigation Satellite System (GLONASS) was developed for the Russian military and was declared operational in 1996.(俄联邦的全球导航卫星系统(GLANASS)是由俄罗斯军方开发的,并在 1996 年宣布运行)Fully deployed GLONASS constellation is composed of 24(21 operational + 3 spares) satellites in three orbital planes whose ascending nodes are 120 degrees apart.(全配置的 GLONASS 星座由 24(21 运行+3 备用)颗卫星在三个轨道平面中,其升交点相差120 度)8 satellites are equally spaced in each plane with argument of latitude displacement of 45degrees(.8 颗卫星平均分布在升交角距相差45 度的每个平面内)Besides the planes themselves have 15 degrees argument of latitude displacement.(此外轨道平面它们自己有 15 度的升交角距差)Each satellite operates in circular 19,100 km orbits at an inclination angle of 64.8 degrees and each satellite completes an orbit in approximately 11 hours 15 minutes.(每个卫星在19100 公里的圆轨道上运转,倾