测绘专业英语原文 译文(20-30)单元测绘专业英语原文 译文(20-30)单元.doc

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