首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
GPS The Global Positioning System is a space-based triangulation system using satellites and computers to measure positions
GPS The Global Positioning System is a space-based triangulation system using satellites and computers to measure positions
admin
2012-12-26
32
问题
GPS
The Global Positioning System is a space-based triangulation system using satellites and computers to measure positions anywhere on earth. It is first and foremost a defense system developed by the United States Department of Defense, and is referred to as the "Navigation Satellite Timing and Ranging Global Positioning System" or NAVSTAR GPS. The uniqueness of this navigational system is that it avoids the limitations of other land-based systems such as limited geographic coverage, lack of continuous 24-hour coverage, and the limited accuracies of other related navigational instruments. The high accuracies obtainable with the Global Positioning System also make it a precision survey instrument.
GPS Components: the Space Segment, the Control Segment, and the User Segment.
Space Segment
The Space Segment of the system consists of the GPS satellites. These space vehicles (SVs) send radio signals from space.
The GPS Operational Constellation consists of 24 satellites that orbit the earth in 12 hours. There are often more than 24 operational satellites as new ones are launched to replace older satellites. The satellite orbits repeat almost the same ground track (as the earth turns beneath them) once each day. The orbit altitude is such that the satellites repeat the same track and area over any point approximately each 24 hours (4 minutes earlier each day). There are six orbital planes (with four SVs in each), equally spaced (60 degrees apart), and inclined at about fifty-five degrees with respect to the equatorial (赤道的) plane. This constellation provides the user with between five and eight SVs visible from any point on the earth.
Control Segment
The Control Segment consists of a system of tracking stations located around the world.
The Master Control facility is located at Schriever Air Force Base (formerly Falcon AFB) in Colorado. These monitor stations measure signals from the SVs which are incorporated into orbital models for each satellites. The models compute precise orbital data and SV clock corrections for each satellite. The Master Control station uploads orbital data and clock data to the SVs. The SVs then send subsets of the orbital ephemeris (星历表) data to GPS receivers over radio signals.
User Segment
The GPS User Segment consists of the GPS receivers and the user community. GPS receivers change SV signals into position, speed, and time estimates. Four satellites are required to compute the four dimensions of X, Y, Z (position) and Time. GPS receivers are used for navigation, positioning, time distribution, and other research.
Navigation in three dimensions is the primary function of GPS. Navigation receivers are made for aircraft, ships, ground vehicles, and for hand carrying by individuals.
Precise positioning is possible using GPS receivers at reference locations providing corrections and relative positioning data for remote receivers. Surveying, geodetic control, and plate tectonic studies are examples.
Time and frequency distribution, based on the precise clocks on board the SVs and controlled by the monitor stations, is another use for GPS. Astronomical observatories, telecommunications facilities, and laboratory standards can be set to precise time signals or controlled to accurate frequencies by special purpose GPS receivers.
Research projects have used GPS signals to measure atmospheric parameters.
GPS Accuracy
At present the system consists of 24 satellites at an altitude of about 20,000 km having an orbital inclination of 55 degrees. The orbits are almost circular and it takes 12 hours for a satellite to complete a pass around the Earth. GPS signals are broadcast from a cluster of 24 or more earth orbiting satellites. Because the GPS signals are derived from the atomic frequency standards on board each satellite, they are widely used as a reference for time synchronization and frequency adjustment. The real time positioning accuracy of a single receiver is normally up to 100 meters horizontally and 150 meters vertically. However, various methods have been developed which enable much higher accuracy (centimeter level).
GPS Receivers
There are a variety of different types of GPS receivers on the market for commercial and public use. Prices range from $500—$30,000, reflecting the accuracy and capabilities of the instruments. For the general outdoorsman, a good GPS receiver should have 8 satellite tracking capability and be capable of receiving the GPS satellite signals through forest covering in northern Ontario shield area; for the professional user, a minimum 8 satellite tracking capability, high memory capacity, differential GPS capability, and resistance to signal weakening under forest covering is essential; for the professional surveyor requiring high level precision and accuracy capability, they should assess the project or application for which the technology is to be used with the help of an unbiased consultant, in order to determine the most cost effective and appropriate instrument.
Navigational Units
Small hand held units at relatively low cost allow boaters and hikers to know their position within a few hundred meters. This accuracy is sufficient for recreational use.
Mapping
A hand held or similar unit at mid-range price that is linked to a fixed broadcast base station. These units allow utility companies, municipalities and others to locate various items (telephone poles, waterlines, valves) with a positional tolerance of several meters. This is suitable for some Geographical Information Systems (GIS) mapping purposes.
GPS and Policing
GPS technology offers numerous benefits to law enforcement agencies of all types. For some agencies, the navigational capabilities offered by GPS enhance efficiency and safety. These navigational applications can be used to support a variety of policing and criminal justice functions. Other agencies use GPS positioning technologies to carry out special operations or to provide enhanced personnel safety.
For example, using computerized maps of their rights given by law, cooperated with GPS, aviation personnel can determine location, speed and time.
The positioning capabilities offered by GPS may also contribute to the success of specialized law enforcement operations such as in controlling vehicles. One such program operated in Minneapolis led to a 60% reduction in auto theft after only one month. The automatic vehicle location systems can not only provide efficiency of response and help ensure officer safety, but also provide officer with accurate information concerning the best response route to an incident. What’s more, they can provide officers information that allows the closest patrol officers to be dispatched to a particular incident.
Advanced Transportation Management Systems (ATMS) are heavily dependant upon GPS technology to provide data about the road system. GPS allows for law enforcement personnel to clear roadway blockages to ensure the safety of motorist.
Most people associate law enforcement with the prevention, reduction, and prosecution of criminal activity. In fact, a large portion of local law enforcement resources are involved in facilitating the movement of people and vehicles in a safe manner.
In conclusion, large-volume commercial applications such as cellular phones, personal communication systems, and in-vehicle navigation systems will fuel continued development of these technologies. What was ultimately the domain of the Department of Defense is rapidly becoming available for business, private, and general government use. Policing and public safety in general, will benefit from these market forces. It is clear that there are a number of GPS applications for policing.
The highest positioning accuracy of a receiver can now reach ______.
选项
A、meter-level
B、kilometer-level
C、centimeter-level
D、millimeter-level
答案
C
解析
原文该段最后一句表明准确度已经可以达到厘米水平,所以本题答案为C。
转载请注明原文地址:https://kaotiyun.com/show/vew7777K
0
大学英语四级
相关试题推荐
ATheSpanishGovernmentissoworriedaboutthenumberofyoungadultsstilllivingwiththeirparentsthatithasdecidedtoh
Teachingtodaydemandsmorethanjustcaringaboutchildrenandknowingone’ssubjectwell.Teachersneedtofindoutwhat【B1】__
Teachingtodaydemandsmorethanjustcaringaboutchildrenandknowingone’ssubjectwell.Teachersneedtofindoutwhat【B1】__
A、Peoplelearnedfromoneanother.B、Peoplesharedeachother’sbeliefs.C、Peopletradedgoodsalongtheroute.D、Peopleearned
Womenareonthevergeofoutnumberingmenintheworkforceforthefirsttime,ahistoricreversalcausedbylong-termchanges
A、Water.B、Crops.C、Money.D、Trees.B由对话中提到的thefarmersdon’thavearealproblemwiththeelephantsuntiltheelephantsstarte
Languageislearnedprimarilythroughcommunicationwithotherpeople.Researchshowsthatthemorecommunicationchildren【S1】__
WhenIfirstentereduniversity,myaunt,whoisanEnglishprofessor,gavemeanewEnglishdictionary.Iwas【C1】______toseet
ThismaycomeasnosurprisetoresidentsofNewYorkCityandotherbigurbancenters:Livingtherecanbebadforyourmental
Asamanager,you’rerequiredtowithstandthecriticismwhendecisionsdon’tturnouttobepopular.Managingleadershipisman
随机试题
注册会计师在整个审计业务中,应严格按照审计准则的要求实施多项审计工作。是审计工作的起点,也是审计工作中最重要的环节()
以下情况下,股票交易会成功的是()
《中华人民共和国固体废物污染环境防治法》规定:()经中华人民共和国过境转移危险废物。
下列关于评价投资项目的回收期法,说法不正确的是()。
在公元之初,牧师们将基督教在整个罗马帝国中传播开来,基督教的普及首先涉及的是各大城市的平民阶层。基督徒们反对皇权意识,因此君主们都把他们视为威胁,并组织起对他们的暴力摧残。然而这并没有中断新信仰的扩展,它一点点赢得了贵族阶级和最有影响力的人士,而且很快触及
当某商品的价格上升2%,其需求量下降10%,则该商品的需求价格弹性是()。
国际金融市场上,美元债券年收益率为8%,英镑债券年收益率为12%,假定两种债券信用等级相同,那么,根据利率平价,在一年内,英镑应相对美元:()
Despiteyourbestintentionsandefforts,itis【C1】______:Atsomepointinyourlife,youwillbewrong.【C2】______canbehard
软件设计中划分模块的一个准则是(60)。两个模块之间的耦合方式中,(61)耦合的耦合度最高,(62)耦合的耦合度最低。一个模块内部的内聚种类中(63)内聚的内聚度最高,(64)内聚的内聚度最低。
A公司向B公司发出—份电文,称C公司要向B公司订购大批棉花,诱使B公司高价向A公司购买大量棉花。这属于安全攻击中的捏造,是对【 】的攻击。
最新回复
(
0
)