外文翻译---GPS全球卫星定位系统

1、.英文文献The Global Positioning SystemThe global Positioning System (GPS) is revolutionizing surveying technology, Like its predecessor , the TEANSIT Doppler system, GPS shifts the scene of surveying operations from ground-to-ground measurements to ground-to-sky , with obvious implications : intervisibi

2、lity of marks is no longer a criteion for their location ; operations are possible in nearly all kinds of weather and be performed during day or night ; and the skills required to utilise the technology are different both in field operations and data processing . But GPS is not merely a replacement

3、for TRANSIT . The simultaneous visibility of multiple satellites allows effective cancellation of the major sources of error in satellite observations , with the result that with GPS, relative positioning accuracies of one part per million(ppm) or better over distances from one kilometer to thousand

4、s of kilometers are possible . This means that GPS can compete with terrestrial techniques over short distances, and can achieve more accurate results in less time than TRANSIT observations over longer distances . GPS was designed primarily as a navigation system, to satisfy both military and civili

5、an needs for real-time positioning. This positioning is accomplished through the use of coded information, essentially clever timing signals, transmitted by the satellites. Each GPS satellite transmits a unique signal on two L-band frequencies: A at 1575.42 MHz and B at 1227.60 MHz(equivalent to wav

6、elengths of approximately 19 and 24 cm, respectively).The satellite signals consist of the L-band carrier waves modulated with a "Standard" or S code (formerly called the C/A code),a "Precise" or P code and a Navigation Message containing, amongst other things ,the coordinat

7、es of the satellites as functions of time-the "Broadcast Ephemerides". The S code which is intended mainly for civilian use , yields a range measurement precision of about 10 meter, The navigation service provided by this code is referred to as the Standard Positioning Service, The p code

8、is intended for military and selected civilian use only and yields a measurement precision of about 1 meter, The navigation service provided by the P code is therefore referred to as the Precise Positioning Service (PPS) Although both codes can be used for surveying , a more accurate method is to me

9、asure the phase of the carrier signal , For this reason , we will not discuss the detailed characteristics of the codes in this monograph . There are currently eight usable satellites in orbit. These are the experimental, ”Block 1” satellites, which will be progressively replaced as the “block 2”, o

10、perational satellites are placed into orbit beginning in 1986.By 1989 the system should be complete, with 18 satellites in six orbital planes-at about 20200 km altitude, allowing for simultaneous visibility of at least four satellites at any time of day almost anywhere in the world. The present cons

11、tellation of satellites is configured to provide the most favorable geometry for testing the system over North America.As it happens, the observation geometry is equally favorable in Australia, and it is possible now to obtain surveying accuracies equal to those obtainable when the system is fully c

12、onfigured, but only for about six hours per day, At the time of writing (November 1985),the period of maximum mutual visibility of the satellites in eastern Australia is between 6 pm and mid-night local time The period regresses by 4minutes per day (or 2 hours per month), returning to the same times

13、 a year from now. This period of useful visibility will increase as additional satellites are launched from late 1985. As with TRANSIT , much higher accuracies are obtained in relative positioning from observations made simultaneously at two observing stations. Consequently , unless otherwise indica

14、ted , all discussion concerning data acquisition and processing will assume a two-receiver configuration. This is often referred to as the differential mode. The position differences so determined constitute the baseline vector or simply the baseline between the points occupied by two receivers .All

15、 satellite positioning systems provide ground coordinates of a receiver (or the baseline vector between a pair of receivers) in an earthcentered coordinate system, The orientation of the system is determined by the tabulated coordinates or ephemeredes of the GPS satellites. In order to relate coordi

16、nates determined by GPS surveying to the local geodetic datum a transformation relationship needs to be established.The following factors influence the final positioning accuracy obtainable with GPS:(1) The precision of the measurement and the receiver-satellite geometry.(2) The measurement processi

17、ng technique adopted.(3) The accuracy with which atmospheric and ionospheric effects can be modeled.(4) The accuracy of the satellites ephemeredes.Each of these factor is discussed briefly in the next three sections.GPS Measurement Types. GPS measurement can be made using either the carrier signal o

18、r the codes. Code measurements are called pseudo-ranges and can be based on either the P code or the S code. Knowledge of the properties of each of these types of measurements is necessary for understanding and evaluating GPS instruments. Pseudo-ranges are the simplest to visualize geometrically , a

19、s they are essentially a measurement of distance contaminated by clock errors. Throughout this monograph, we use the terms clock , frequency standard and oscillator to denote the same thing , namely , a device for precisely measuring a time interval. When four satellites are observed simultaneously

20、, it is possible to determine the three-dimensional position of the ground receiver, and the receiver clock offset, at a single epoch . This is simply resection by distance, in surveying terminology , with the satellites serving as the control station, As with the resection technique, the precision

21、is a function of the geometry of the receiver in relation to the four visible satellites. The best geometry would be when the satellites are in each of the four quadrants and each at an elevation angle of 40°-70°above the horizon. However , pseudo-range measurements are not nearly as preci

22、se as phase measurements of the carrier wave itself . In order to achieve position accuracies of 10 meter from P code measurements or 100 meter from S code measurements ( adequate for navigation ) , it was only necessary to design a code structure which allowed metre level measurement precision . Mo

23、rever , the more precise P code will likely be encrypted , and may therefore not be available for non-military use , when the system becomes fully operational in 1989 . An additional impediment to accueate pseudo-ranging arises from multipath effects , that is the tendency of some fraction of the sa

24、tellite signal to reach the receiver antenna via reflection off the ground or other surfaces . The size and signature of multipath effects depend on antenna design and height of the antenna above ground but probably cannot be reduced below a few decimeters with practical configurations . Carrier pha

25、se can be determined from the code-modulated signal either by using the code or other techniques . The L1 signal , which has both P code and S code modulation , can thus be tracked with S or P code receivers or with codeless receivers . The L2 signal , useful for removing ionospheric effects for ver

26、y precise applications (< 2 ppm for relative positioning ) , has no S code modulation , so that receivers for these applications must either have P code capability or operate without code . It is also possible to track the phase of the 10.23 MHz P code transition signal or P code sub-carrier with

27、out knowledge of the codes . The long wavelength ( approximately 30 meter ) of this signal compared with the L-band carrier allows relatively easy resolution of the integer-cycle ambiguity , producing in effect a pseudo-range measurement . However , the long wavelength makes the measurements more su

28、sceptible to multipath effects , roughly to the same degree as pseudo-range measurements . 中文文献GPS全球卫星定位系统全球性定位系统(GPS) 是一种革命化勘测技术, 像它的前辈, TRANSIT 子午仪多普勒系统（TRANSIT）, GPS 转移勘测的操作场面从地地测量到地面对天空测量, 以明显的涵义: 几乎所有是操作都可以在各种天气和昼夜完成；在野外观测和数据处理中所需要的技能和技术是不同的。 但GPS 不仅仅是替换子午仪多普勒系统（TRANSIT）。 在观测卫星是能同时看到多颗卫星，使得各种主要

29、误差得到了有效消除，因而在一公里到数千公里的距离上，GPS的相对定位精度可能达到1ppm或者更好。 这意味着, GPS地面技术能应用在短距离上，而且在长距离GPS获得高精度结果的时间比子午仪多普勒系统（TRANSIT）要短。GPS 被设计了主要作为导航系统, 满足两个对实时安置的军事和平民需要。 这安置是完成通过对被编码的信息的用途, 根本上聪明定时信号, 由卫星传输。 各枚GPS卫星传输一个独特的信号在二个L 波段频率: L1 是1575.42 兆赫和L2是1227.60 MHz（各自大约19 和24 cm 波长）, 卫星信号包括L 波段载体波浪调整以"标准" 或S 代码

30、(以前称C/代码),导航电文信息包含在P码中，卫星的坐标作为时间，也就是 "广播星历表" 。 S码中的信息主要是为民用服务，产生范围测量精确度大约10 米, 航海也由这个代码提供标准定位服务, P代码主要是为军事和被选择的某些民用方面服务，产生范围测量精度大约1米，航海由这个代码提供精确定位服务 虽然两个代码都能用来测量，但有一种更加准确的方法是测量载体信号, 因此, 我们不会谈论详细代码的特征在这篇专题论文里。 目前有八枚能用的卫星在轨道运行。从1986年开始，“Block 1”试验卫星将被“Block 2”工作卫星取代。到1989年，该系统就应该建立完成了，将有18颗卫

31、星在距离地球20200公里高度的六个轨道运行，如果这样的话，在世界的任何一个地方任何时间都至少能接收到4颗以上的卫星。在当地时间下午6点和午夜之间，卫星的最大相互可见性出现在东澳大利亚。这个时间每天退后4分钟（也就是一个月退后2小时），从现在返回到次年。当从1985年晚些时候卫星再被发射后， 这个有用的可见性的期间将增加。正如子午仪多普勒系统，GPS在两个测站上可以同时获得更高精度的相对定位结果。如果这样，所有的关于数据采集和处理的任务将由一台双频接收机承担，这就是常说的差分定位。 由这样确定的定位误差构成了基础线传染媒介或简单地基础线，即由两台接收机所确定的。在地心坐标系中，所有卫星定位系统提供接收机的地面坐标(或基础线传染媒介在一对接收器之间)