测绘工程专业英语(-) 作者： 日期：2 测绘工程专业英语全文翻译（Unit2030）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: the space segment: the GPS satellitesthemselves, the control segment, operated by the U .S. military, and the user segment,which includes both military and civilian users and their GPS equipments（.GPS 由三个部分组成：太空部分：GPS 卫星自己，地面控制部分，由美国军方控制，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 的大部分民用用途，分为三种类型：导航、定位和授时。）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