求关于GPS的文章要求是：原文是中文的,并有相应的英文翻译；或是英文是原文的,并有相应的中文翻译.

求关于GPS的文章
要求是：原文是中文的,并有相应的英文翻译；或是英文是原文的,并有相应的中文翻译.

导 航 基 础
一、GPS定位原理
二、GPS系统介绍
三、差分GPS定位技术与原理
四、卫星导航知识
五、无源BD定位
六、专业词语
一、GPS定位原理
1．概述
五十年代未,原苏联发射了人类的第一颗人造地球卫星,美国科学家在对其的跟踪研究中,发现了多普勒频移现象,并利用该原理促成了多普勒卫星导航定位系统TRANsIT的建成,在军事和民用方面取得 了极大的成功,是导航定位史上的一次飞跃,我国也曾引进了多台多普勒接收机,应用于海岛联测、地球勘探等领域.但由于多普勒卫星轨道高度低、信号载波频率低,轨道精度难以提高,使得定位精度较 低,以满足大地测量或工程测量的要求,更不可能用于天文地球动力学研究.为了提高卫星定位的精度 ,美国从1973 年开始筹建全球定位系统GPS（Global Positioning System）.在进过了方案论证、系统 试验阶段后,于1989年开始发射正式工作卫星,并于1994年全部建成,投入使用.GPS系统的空间部分由 21颗卫星组成,均匀分布在6个轨道面上,地面高度为20000余公里,轨道倾角为55度,扁心率约为0,周 期约为12小时,卫星向地面发射两个波段的载波信号,载波信号频率分别为1575.442兆 赫兹（L1波段） 和1227.6兆赫兹（L2波段）,卫星上安装了精度很高的原子钟,以确保频率的稳定性,在载波上调制有 表示卫星位置 的广播星历,用于测距的C/A码和P码,以及其它系统信息,能在全球范围内,向任意多用 户提供高精度的、全天候的、连续的、实时的三维测速、三维定位和授时. GPS系统的控制部分由设在美国本土的5个监控站组成,这些站不间断地对GPS卫星进行观测,并将计 算和预报的信息由注入站对卫星信息更新. GPS系统的用户是非常隐蔽的,它是一种单程系统,用户只接收而不必发射信号,因此用户的数量也 是不受限制的.虽然GPS系统一开始是为军事目的而建立的,但很快在民用方面得到了极大的发展,各类GPS接收机和处理软件纷纷涌现出来.目前在中国市场上出现的接收机主要有NovAtel、ASHTECH、 TRIMBLE、CMC等.能对两个频率进行观测的接收机称为双频接收机,只能对一个频率进行观测的接收机 成为单频接收机,他们在精度和价格上均有较大区别. 对于测绘界的用户而言, GPS已在测绘领域引起了革命性的变化,目前,范围上数公里至几千公里的 控制网或形变监测网,精度上从百米至毫米级的定位,一般都将GPS作为首选手段,随着RTK技术的日趋 成熟,GPS已开始向分米乃至厘米级的放样、高精度动态定位等领域渗透. 国际GPS大地测量和地球动力学服务IGS自1992年起,已在全球建立了多个数据存储及处理中心和百余 个常年观测的台站,我国也设立了上海余山、武汉、西安、拉萨、台湾等多个常年观测台站,这些台站的观测数据每天通过INTERNET网传向美国的数据存储中心,IGS还几乎实时地综合各数据处理中心的结果 ,并参与国际地球自转服务IERS的全球坐标参考系维护及地球自转参数的发布.使用者也可免费从 INTERNET网上取得观测数据及精密星历等产品. GPS系统的实时导航定位精度很高,美国在1992年起实行了所谓的SA政策,即降低广播星历中卫星位 置的精度,降低星钟改正数的精度,对卫星基准频率加上高频的抖动（使伪距和相位的量测精度降低） ,后又实行了A-S政策,即将P码改变为Y码,即对精密伪距测量进一步限制,而美国军方和特许用户不受 这些政策的影响,但美国为了获得更大的商业利益,这些政策终将被取消.——中文（注!：这是第一段的 第2、3段请见参考资料,需要的话我再给翻译）
Guide navigation base spell
A, GPS positioning principle
Second, GPS system is introduced
Three, differential GPS technology and principle
Four, satellite navigation knowledge
Five, the passive BD positioning
Six, professional words
A, GPS positioning principle
1. Outlines
In the 1950s, the former Soviet union without launched human first man-made earth satellite, American scientists on its tracking study, discovered the doppler frequency shift, and using the principle contributed to doppler satellite navigation and positioning system of TRANsIT, was built in military and civilian aspects has achieved great success, navigation and positioning in the history of a leap, our country also has introduced more Taiwan doppler receiver, used in the coastlands couplet measurement, earth exploration, etc. But because doppler satellite orbital altitude low signal to the carrier frequency low orbit precision hard to improve, low precision, make positioning, in order to satisfy geodesy or engineering measurement requirements, the more impossible for astronomical earth dynamics research. In order to improve the precision of the American satellite Positioning, from 1973 begin to prepare the Global Positioning System (GPS Positioning System) Global optimisation techniques. The scheme in entered demonstration, system test phase, in 1989 starts to send a formal working satellite, and completed in 1994, put into use. GPS system of space partly by 21 satellite composition, evenly distributed in 6 orbit plane, ground height for 20,000 kilometers, orbit for 55 degrees obliquity, flat heart rate is about 0, zhou period is about 12 hours, satellite to the ground to launch two bands carrier signal, carrier signal frequency respectively 1575.442 trillion Hertz (L1 band) and 1227.6 MHZ (L2 band), satellite fitted precision is high, so as to ensure the clocks in carrier frequency stability, the modulation has said the satellite location of broadcast star calendar, used for ranging C/A code and P yards, and other system information, can in the global scope, towards any multi-purpose families to provide high-precision, all-weather, continuously, real-time three-dimensional velocimetry and 3d position and GPS clock. GPS system control in part by the native American five monitor composition, these stood incessantly on GPS satellites observation, and will calculate and forecast the project by injection station of satellite information information updates. GPS system of the users are very covert, it is a one-way system users receive only without transmitting signal, so the user and the number of is not restricted. Although GPS system a first for military purpose built in consumer, but soon got huge development, all kinds of GPS receiver and processing software have emerged. Be in China at present that appeared on the market basically has NovAtel, receiver, ASHTECH TRIMBLE, CMC etc. Can two frequencies were observed on the receiver called double-frequency receivers, can only be placed on one frequency observation of the receiver become single receivers in precision and price, they all have great differences. For CeHuiJie user is concerned, GPS surveying and mapping field already in caused a revolutionary change, at present, the scope of several kilometers to thousands of kilometers of control network or deformation monitoring network, accuracy from 100 meters to mm level commonly will GPS positioning, as the preferred means, with RTK technology matures, GPS has begun to honour and even the cm-level lofting, high precision dynamic positioning fields penetration. International GPS geodesy and geodynamics service IGS since 1992, has established a global multiple data storage and processing center and onhundred perennial observation stations, China also set up the Shanghai over mountains, wuhan, xian, Lhasa, Taiwan etc. Several perennial observation stations, these stations of observation data every day by INTERNET nets good-health to American data storage centers, IGS almost real-time synthesizes each data processing center, the result of the earth's rotation and participate in international service IERS global coordinates TRS maintenance and the earth rotation parameters release. Users can also be free from INTERNET made observation data and precise star calendar etc. Product. GPS real-time navigation and positioning precision is high, the United States in 1992 into effect in the so-called SA policy, namely reducing broadcast star calendar in satellite bits inverted precision, reduce the number of stars clock correction precision, high frequency of satellite benchmark frequency plus the jitter (make pseudorange and phase measurement accuracy reduced), and then execute the A - S policy, forthcoming P yards change is Y yards, i.e. on precision pseudorange measurement further restriction, and the U.S. military and concessionary users not affected by these policy influence, but the United States in order to get more business interests, these policies will be cancelled.