全球定位系統(tǒng)的介紹 外文翻譯

1、<p>　　畢 業(yè) 設(shè) 計（論 文）外 文 參 考 資 料 及 譯 文</p><p>　　譯文題目：Introduction to the Global Positioning System </p><p>　　全球定位系統(tǒng)的介紹 </p><p>　　學(xué)生姓名： 學(xué) 號

2、： </p><p>　　?！　I(yè)： 通信工程 </p><p>　　所在學(xué)院： </p><p>　　指導(dǎo)教師：

3、 </p><p>　　職　　稱： </p><p>　　201x年 xx月xx日</p><p>　　Introduction to the Global Positioning System </p><p>　　---------From “Corvall

4、is Microtechnology, Inc. 1996”</p><p>　　Chapter One: What is GPS?</p><p>　　The Global Positioning System (GPS) is a location system based on a constellation of about 24 satellites orbiting the e

5、arth at altitudes of approximately 11,000 miles. GPS was developed by the United States Department of Defense (DOD), for its tremendous application as a military locating utility. The DOD's investment in GPS is immen

6、se. Billions and billions of dollars have been invested in creating this technology for military uses. However, over the past several years, GPS has proven to be a u</p><p>　　GPS satellites are orbited high

7、enough to avoid the problems associated with land based systems, yet can provide accurate positioning 24 hours a day, anywhere in the world. Uncorrected positions determined from GPS satellite signals produce accuracies

8、in the range of 50 to 100 meters. When using a technique called differential correction, users can get positions accurate to within 5 meters or less.</p><p>　　Today, many industries are leveraging off the DO

9、D's massive undertaking. As GPS units are becoming smaller and less expensive, there are an expanding number of applications for GPS. In transportation applications, GPS assists pilots and drivers in pinpointing thei

10、r locations and avoiding collisions. Farmers can use GPS to guide equipment and control accurate distribution of fertilizers and other chemicals. Also，GPS is used for providing accurate locations and as a navigation tool

11、 for hikers, hun</p><p>　　Many would argue that GPS has found its greatest utility in the field of Geographic Information Systems (GIS). With some consideration for error, GPS can provide any point on earth

12、with a unique address (its precise location). A GIS is basically a descriptive database of the earth (or a specific part of the earth). GPS tells you that you are at point X,Y,Z while GIS tells you that X,Y,Z is an oak t

13、ree, or a spot in a stream with a pH level of 5.4. GPS tells us the "where". GIS tells us the "what</p><p>　　Chapter Two: Trilateration - How GPS Determines a Location</p><p>　　In

14、 a nutshell, GPS is based on satellite ranging - calculating the distances between the receiver and the position of 3 or more satellites (4 or more if elevation is desired) and then applying some good old mathematics. As

15、suming the positions of the satellites are known, the location of the receiver can be calculated by determining the distance from each of the satellites to the receiver. GPS takes these 3 or more known references and mea

16、sured distances and "triangulates" an additional position.</p><p>　　As an example, assume that I have asked you to find me at a stationary position based upon a few clues which I am willing to give

17、 you. First, I tell you that I am exactly 10 miles away from your house. You would know I am somewhere on the perimeter of a sphere that has an origin as your house and a radius of 10 miles. With this information alone,

18、you would have a difficult time to find me since there are an infinite number of locations on the perimeter of that sphere.</p><p>　　Second, I tell you that I am also exactly 12 miles away from the ABC Groce

19、ry Store. Now you can define a second sphere with its origin at the store and a radius of 12 miles. You know that I am located somewhere in the space where the perimeters of these two spheres intersect - but there are st

20、ill many possibilities to define my location.</p><p>　　Adding additional spheres will further reduce the number of possible locations. In fact, a third origin and distance (I tell you am 8 miles away from th

21、e City Clock) narrows my position down to just 2 points. By adding one more sphere, you can pinpoint my exact location. Actually, the 4th sphere may not be necessary. One of the possibilities may not make sense, and ther

22、efore can be eliminated.</p><p>　　For example, if you know I am above sea level, you can reject a point that has negative elevation. Mathematics and computers allow us to determine the correct point with onl

23、y 3 satellites.</p><p>　　Based on this example, you can see that you need to know the following information in order to compute your position:</p><p>　　A) What is the precise location of three o

24、r more known points (GPS satellites)?B) What is the distance between the known points and the position of the GPS receiver?</p><p>　　Chapter Three: How the Current Locations of GPS Satellites are Determined

25、</p><p>　　GPS satellites are orbiting the Earth at an altitude of 11,000 miles. The DOD can predict the paths of the satellites vs. time with great accuracy. Furthermore, the satellites can be periodically a

26、djusted by huge land-based radar systems. Therefore, the orbits, and thus the locations of the satellites, are known in advance. Today's GPS receivers store this orbit information for all of the GPS satellites in wha

27、t is known as an almanac. Think of the almanac as a "bus schedule" advising you of wher</p><p>　　The Department of Defense constantly monitors the orbit of the satellites looking for deviations fro

28、m predicted values. Any deviations (caused by natural atmospheric phenomenon such as gravity), are known as ephemeris errors. When ephemeris errors are determined to exist for a satellite, the errors are sent back up to

29、that satellite, which in turn broadcasts the errors as part of the standard message, supplying this information to the GPS receivers.</p><p>　　By using the information from the almanac in conjuction with the

30、 ephemeris error data, the position of a GPS satellite can be very precisely determined for a given time.</p><p>　　Chapter Four: Computing the Distance Between Your Position and the GPS Satellites</p>

31、<p>　　GPS determines distance between a GPS satellite and a GPS receiver by measuring the amount of time it takes a radio signal (the GPS signal) to travel from the satellite to the receiver. Radio waves travel at

32、the speed of light, which is about 186,000 miles per second. So, if the amount of time it takes for the signal to travel from the satellite to the receiver is known, the distance from the satellite to the receiver (dista

33、nce = speed x time) can be determined. If the exact time when the signal</p><p>　　In order to do this, the satellites and the receivers use very accurate clocks which are synchronized so that they generate t

34、he same code at exactly the same time. The code received from the satellite can be compared with the code generated by the receiver. By comparing the codes, the time difference between when the satellite generated the co

35、de and when the receiver generated the code can be determined. This interval is the travel time of the code. Multiplying this travel time, in seconds, by 1</p><p>　　Chapter Five: Four (4) Satellites to give

36、a 3D position</p><p>　　In the previous example, you saw that it took only 3 measurements to "triangulate" a 3D position. However, GPS needs a 4th satellite to provide a 3D position. Why??</p>

37、<p>　　Three measurements can be used to locate a point, assuming the GPS receiver and satellite clocks are precisely and continually synchronized, thereby allowing the distance calculations to be accurately determ

38、ined. Unfortunately, it is impossible to synchronize these two clocks, since the clocks in GPS receivers are not as accurate as the very precise and expensive atomic clocks in the satellites. The GPS signals travel from

39、the satellite to the receiver very fast, so if the two clocks are off by </p><p>　　The atomic clocks aboard the satellites maintain their time to a very high degree of accuracy. However, there will always be

40、 a slight variation in clock rates from satellite to satellite. Close monitoring of the clock of each satellite from the ground permits the control station to insert a message in the signal of each satellite which precis

41、ely describes the drift rate of that satellite's clock. The insertion of the drift rate effectively synchronizes all of the GPS satellite clocks.</p><p>　　The same procedure cannot be applied to the cloc

42、k in a GPS receiver. Therefore, a fourth variable (in addition to x, y and z), time, must be determined in order to calculate a precise location. Mathematically, to solve for four unknowns (x,y,z, and t), there must be f

43、our equations. In determining GPS positions, the four equations are represented by signals from four different satellites.</p><p>　　Chapter Six: The GPS Error Budget</p><p>　　The GPS system has

44、been designed to be as nearly accurate as possible. However, there are still errors. Added together, these errors can cause a deviation of +/- 50 -100 meters from the actual GPS receiver position. There are several sourc

45、es for these errors, the most significant of which are discussed below:</p><p>　　Atmospheric Conditions</p><p>　　The ionosphere and troposphere both refract the GPS signals. This causes the spee

46、d of the GPS signal in the ionosphere and troposphere to be different from the speed of the GPS signal in space. Therefore, the distance calculated from "Signal Speed x Time" will be different for the portion o

47、f the GPS signal path that passes through the ionosphere and troposphere and for the portion that passes through space.</p><p>　　As mentioned earlier, GPS signals contain information about ephemeris (orbital

48、 position) errors, and about the rate of clock drift for the broadcasting satellite. The data concerning ephemeris errors may not exactly model the true satellite motion or the exact rate of clock drift. Distortion of th

49、e signal by measurement noise can further increase positional error. The disparity in ephemeris data can introduce 1-5 meters of positional error, clock drift disparity can introduce 0-1.5 meters of pos</p><p&

50、gt;　　Ephemeris errors should not be confused with Selective Availability (SA), which is the intentional alteration of the time and ephemeris signal by the Department of Defense. </p><p>　　A GPS signal bounci

51、ng off a reflective surface prior to reaching the GPS receiver antenna is referred to as multipath. Because it is difficult to completely correct multipath error, even in high precision GPS units, multipath error is a se

52、rious concern to the GPS user.</p><p>　　Chapter Seven: Measuring GPS Accuracy</p><p>　　As discussed above, there are several external sources which introduce errors into a GPS position. While th

53、e errors discussed above always affect accuracy, another major factor in determining positional accuracy is the alignment, or geometry, of the group of satellites (constellation) from which signals are being received. Th

54、e geometry of the constellation is evaluated for several factors, all of which fall into the category of Dilution Of Precision, or DOP.</p><p>　　DOP is an indicator of the quality of the geometry of the sate

55、llite constellation. Your computed position can vary depending on which satellites you use for the measurement. Different satellite geometries can magnify or lessen the errors in the error budget described above. A great

56、er angle between the satellites lowers the DOP, and provides a better measurement. A higher DOP indicates poor satellite geometry, and an inferior measurement configuration.</p><p>　　Some GPS receivers can a

57、nalyze the positions of the satellites available, based upon the almanac, and choose those satellites with the best geometry in order to make the DOP as low as possible. Another important GPS receiver feature is to be ab

58、le to ignore or eliminate GPS readings with DOP values that exceed user-defined limits. Other GPS receivers may have the ability to use all of the satellites in view, thus minimizing the DOP as much as possible.</p>

59、;<p>　　全球定位系統(tǒng)的介紹 </p><p>　　----摘自Corvallis Microtechnology公司，1996</p><p><b>　?。菏裁词荊PS？</b></p><p>　　全球定位系統(tǒng)（ＧＰＳ）是一種基于２４顆高度大約１１０００英里的地球軌道衛(wèi)星的定位系統(tǒng)。

60、ＧＰＳ是美國國防部（ＤＯＤ）因?yàn)槠湓谲娛露ㄎ谎b置方面巨大的應(yīng)用而開發(fā)的。國防部對ＧＰＳ的投入是極大的。已經(jīng)有數(shù)十億美元的投資為了開發(fā)這種軍事應(yīng)用技術(shù)。然而，過去一段時間以來，ＧＰＳ已經(jīng)被證實(shí)是在測繪非軍事地圖應(yīng)用方面十分有用的工具。</p><p>　　GPS衛(wèi)星的軌道足夠高以避免以土地為基礎(chǔ)的系統(tǒng)相關(guān)的問題，還可以在世界上任何地方提供每天24小時準(zhǔn)確的定位。在裸眼可視位置GPS衛(wèi)星信號產(chǎn)生的定位精度為５０到１０

61、０米。當(dāng)使用差分技術(shù)時，用戶可以得到精度為5米以下的定位。　　</p><p>　　今天，許多行業(yè)都促使國防部改變。由于GPS單位正變得更小，更便宜，GPS的應(yīng)用正在不斷增加。在交通運(yùn)輸應(yīng)用方面，GPS協(xié)助飛行員和司機(jī)準(zhǔn)確定位它們的位置，避免碰撞。農(nóng)民可以使用GPS引導(dǎo)設(shè)備并且控制化肥和其他化學(xué)品的準(zhǔn)確分布。此外，GPS用于提供準(zhǔn)確的位置，并作為徒步旅行者，獵人和船民的導(dǎo)航工具。</p><p

62、>　　很多人認(rèn)為，GPS已經(jīng)在地理信息系統(tǒng)（GIS）領(lǐng)域發(fā)揮最大的應(yīng)用。在考慮到一些誤差的情況下，GPS可以提供地球上任何一點(diǎn)的唯一一個地址（它的精確位置）。 GIS從根本上說是地球的一個描述的數(shù)據(jù)庫（或地球的特定部分）。 GPS會告訴你，你是在點(diǎn)X，Y，Z，而GIS告訴你，X，Y，Z點(diǎn)是一棵橡樹，或河流中的一個pH值5.4的點(diǎn)。 GPS告訴我們，“在哪里”， GIS告訴我們“是什么”。 GPS/ GIS正在重塑定位，管理，分析，

63、并且映射我們的資源。</p><p>　?。喝叾ㄎ弧狦PS是怎樣定位的</p><p>　　簡單地說，GPS是基于衛(wèi)星測距 -計算接收器和3顆或更多顆衛(wèi)星（4個或更多，如果需要高程）之間的距離，然后用一些以前的正確數(shù)字進(jìn)行計算。假設(shè)衛(wèi)星的位置是已知的，通過確定每個衛(wèi)星到接收機(jī)的距離，可以計算出接收機(jī)的位置。 GPS用這3個或更多的已知的參考和測量距離然后“三角測量”出額外的位置。<

64、;/p><p>　　作為一個例子，假設(shè)我要你根據(jù)我給你提供的很少的一些線索讓你在一個固定的位置找到我。首先，我告訴你，我離你的房子正好是10英里遠(yuǎn)。你會知道我在一個以你的房子為圓心，半徑10英里的球形邊界的地方。只有這些信息，你很難找到我，因?yàn)樵谶@球形的邊界上有無數(shù)的位置點(diǎn)。</p><p>　　第二，我告訴你，我也正好離ABC雜貨店12英里遠(yuǎn)。現(xiàn)在，你可以畫出一個以雜貨店為圓心，半徑12英里

65、的球形。你知道，我所在的地方，在兩個球形空間的周長交叉的地方 - 但我的位置還是有很多的可能性。</p><p>　　添加更多的范圍將進(jìn)一步減少可能的地點(diǎn)。事實(shí)上，第三個圓心和距離（我告訴你是8英里遠(yuǎn)的城市時鐘）使我的位置縮小到只有2點(diǎn)。再增加一個范圍，你可以找出我的確切位置。其實(shí)，第四球體可能不是必需的。其中一個可能是沒有意義的，并因此可以被消除。</p><p>　　例如，如果你知道我

66、是海平面上，你可以拒絕一個海拔為負(fù)的點(diǎn)。數(shù)學(xué)和計算機(jī)讓我們能夠只用3顆衛(wèi)星確定正確的點(diǎn)。</p><p>　　基于這個例子，你可以明白，你需要知道以下信息，以便計算你的位置：</p><p>　　A）3個或更多的已知點(diǎn)（GPS衛(wèi)星）的精確位置是什么？</p><p>　　B）已知點(diǎn)的位置和GPS接收器之間是多少距離？</p><p>　?。喝?/p>

67、何確定GPS衛(wèi)星當(dāng)前位置</p><p>　　GPS衛(wèi)星在高度為11000公里的軌道繞地球飛行。國防部可以非常準(zhǔn)確地預(yù)測衛(wèi)星的路徑與時間的關(guān)系。此外，衛(wèi)星還可以定期通過巨大的陸基雷達(dá)系統(tǒng)進(jìn)行調(diào)整。因此，軌道，衛(wèi)星的位置，都是預(yù)先已知的。今天的GPS接收器存儲所有的GPS衛(wèi)星的軌道信息，被稱為星歷。你的星歷像“巴士時刻表”，提醒你每顆衛(wèi)星在一個特定的時間點(diǎn)在什么地方。每個GPS衛(wèi)星不斷廣播星歷。你的GPS接收器會自

68、動收集這些信息，并將其存儲以供將來參考。</p><p>　　國防部不斷地監(jiān)視衛(wèi)星的軌道預(yù)測值的偏差。任何偏差（由于自然的大氣現(xiàn)象，如重力），被稱為星歷誤差。當(dāng)被確定為存在衛(wèi)星星歷誤差，誤差被發(fā)送備份到該衛(wèi)星，依次將錯誤作為標(biāo)準(zhǔn)的消息的一部分廣播，提供這種信息給GPS接收機(jī)。</p><p>　　通過使用星歷表的信息誤差數(shù)據(jù)，可以很精確地在一個給定的時間確定GPS衛(wèi)星的位置。</p&

69、gt;<p>　?。河嬎隳愕奈恢煤虶PS衛(wèi)星之間的距離</p><p>　　GPS通過測量衛(wèi)星和接收機(jī)之間無線電信號（GPS信號）傳輸所花費(fèi)的時間來確定衛(wèi)星和接收機(jī)的距離。無線電波以光速傳播，這是大約每秒186,000英里的速度。因此，如果信號從衛(wèi)星到接收機(jī)的時間量是已知的，衛(wèi)星到接收機(jī)的距離（距離=速度×時間）可以被確定。如果信號發(fā)送和收到的時間確定，信號的</p><

70、;p><b>　　傳輸時間才能確定。</b></p><p>　　為了做到這一點(diǎn)，衛(wèi)星和接收機(jī)使用非常精確的同步時鐘，以便它們在完全相同的時間，生成相同的代碼。從衛(wèi)星接收的代碼可以跟接收器產(chǎn)生的代碼進(jìn)行比較。通過比較代碼，衛(wèi)星產(chǎn)生代碼時與接收機(jī)接收后產(chǎn)生代碼之間的時間差可以被確定。這個時間間隔為代碼的旅行時間。每秒186,000英里的速度乘以這個時間間隔就是接收機(jī)位置與衛(wèi)星之間的距離。

71、</p><p>　?。核念w衛(wèi)星定位3D位置</p><p>　　在前面的例子中，你看到了，只用了3個測量“三角測量”三維位置。然而，GPS需要第四個衛(wèi)星提供三維位置。為什么？</p><p>　　三個測量值可以用來定位一個點(diǎn)，假設(shè)GPS接收機(jī)和衛(wèi)星時鐘是精確和連續(xù)的同步的，從而使計算出阿里的距離非常精確。不幸的是，這兩個時鐘是不可能同步的，因?yàn)镚PS接收機(jī)中的時鐘

72、是不像非常精確和昂貴的衛(wèi)星原子鐘那樣精確的。GPS信號從衛(wèi)星到接收機(jī)的速度非?？?，所以，如果兩個時鐘是不同步的，即使只有一小部分，所確定的位置數(shù)據(jù)也會大大失真。</p><p>　　船上的衛(wèi)星的原子鐘保持自己的時間在一個非常高的精確度。然而，衛(wèi)星與衛(wèi)星之間的時鐘速率總是會有輕微的變化。從地面關(guān)閉監(jiān)測每顆衛(wèi)星的時鐘使得控制站能在每個衛(wèi)星的信號中插入精確地描述了該衛(wèi)星的時鐘漂移率的消息。有效的漂移速率的插入同步了的所

73、有GPS衛(wèi)星的時鐘。</p><p>　　相同的程序不能被施加到一個GPS接收器中的時鐘上。因此，第四個變量（除了為x，y和z），時間，必須確定，以計算一個精確的位置。在數(shù)學(xué)上，解決四個未知數(shù)（x，y和z，和t），必須有四個方程。在確定GPS定位上，四個方程表示從四個不同衛(wèi)星的信號。</p><p><b>　　第六章：GPS誤差</b></p><

74、;p>　　GPS系統(tǒng)已被設(shè)計為盡可能接近盡可能準(zhǔn)確。然而，仍然有誤差。這些錯誤加在一起可能會導(dǎo)致實(shí)際的GPS接收器的位置偏差為+ / - 50 -100米。這些錯誤的來源有幾個，其中最重要的如下：</p><p><b>　　大氣環(huán)境</b></p><p>　　電離層和對流層都折射GPS信號。這會導(dǎo)致從空間中傳輸?shù)腉PS信號的速度與電離層和對流層中的GPS信號

75、的速度是不同的。因此，從“信號速度×時間”的計算的距離將是不同的GPS信號的路徑，穿過電離層和對流層的部分，其通過空間的部分。</p><p>　　正如前面提到的，GPS信號包含有關(guān)下列內(nèi)容的信息的星歷表（軌道位置）的錯誤，和有關(guān)的廣播衛(wèi)星的時鐘漂移的速率。星歷誤差的數(shù)據(jù)可能不完全模擬真實(shí)的的衛(wèi)星運(yùn)動或時鐘漂移的準(zhǔn)確率。測量噪聲的信號失真，可以進(jìn)一步增加的位置誤差。星歷數(shù)據(jù)的差距可以推出1-5米的位置誤

76、差，時鐘漂移差距引起0-1.5米的位置誤差，測量噪聲可以導(dǎo)致0-10米的誤差。</p><p>　　星歷誤差不應(yīng)該與選擇可用性（SA）混淆，SA是國防部對信號的時間和星歷的蓄意篡改。</p><p>　　多個反射面到達(dá)GPS接收機(jī)天線之間的GPS信號被稱為多徑。因?yàn)樗请y以完全糾正，即使在高精確度的GPS單元也有多路徑誤差，多路徑誤差的是GPS用戶的一個嚴(yán)重的問題。</p>

77、<p>　　第七章：測量GPS精度</p><p>　　如上所討論的，有幾個外部來源引起了GPS位置的誤差。雖然上面討論的誤差總是會影響精度，確定定位精度的另一個主要因素是正在接收信號的一組衛(wèi)星（星座）的排布或幾何分布。星座的幾何形狀被幾個因素評價，所有這些都?xì)w入精度稀釋的類別中，或稱為DOP。</p><p>　　DOP是的衛(wèi)星星座的幾何形狀的質(zhì)量的指標(biāo)。您的計算出的位置可能有

78、所不同，這取決于使用的用于測量的衛(wèi)星。不同的衛(wèi)星的幾何形狀，可以放大或減少上述誤差預(yù)算中的錯誤。衛(wèi)星之間的更大的角度會降低DOP，并提供了一個更好的測量量。較高的DOP表示衛(wèi)星排列位置不合理和一種低劣的測量結(jié)構(gòu)。</p><p>　　一些GPS接收器可以根據(jù)歷書分析可用衛(wèi)星的位置，并選擇這些衛(wèi)星的最佳幾何形狀，以盡可能DOP使降低。 GPS接收器的另一個重要的特點(diǎn)是可以忽略或消除超過用戶定義的限制受DOP影響的G