Unit 20 Understanding 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【Department OF Defense】管理【operated 运转、操作】，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 any application that requires location coordinates.（任何拥有一台GPS 接收机的人都可以使用【access】这套系统，可以应用于任何需要位置坐标的工作中【be used for 用来做】） The GPS system consists of three segments: ⑴the space segment: the GPS satellites themselves, 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【consist of 由„„组成】三个部分【segment 部分、节】组成：⑴太空部分：GPS 卫星自己，⑵地面控制部分，由美国军方【military原意军方的，这里词性转变了——军方n.】控制，⑶用户【user】部分，包括军方和民用【civilian 民用；civil 民用的—civil engineering】用户和他们的装备。） Space Segment: The GPS Constellation（太空部分：GPS 星座【或 GPS 星群】） 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【Air Force】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 ...
