測繪類外文資料翻譯--自動定位技術(shù) (2)

1、<p><b>　　中文6460字</b></p><p><b>　　畢業(yè)設(shè)計（論 文）</b></p><p><b>　　外文資料原文與翻譯</b></p><p><b>　　院 系：</b></p><p><b>　　

2、專業(yè)班級：</b></p><p><b>　　學(xué) 號：</b></p><p><b>　　學(xué)生姓名：</b></p><p><b>　　指導(dǎo)老師：</b></p><p>　　Automatic Position Determination</p&

3、gt;<p>　　1 Position Determination</p><p>　　The traditional method for the direct determination of position has been by astronomical observation. The relative positions and movements of the stars as w

4、ell catalogued and so with a combination of altitude, direction and time observations to the stars, the position in terms of latitude and longitude of a ground station can be calculated. There if less call for direct pos

5、ition determination nowadays since most countries are covered by a primary horizontal control scheme, and the absolute posit</p><p>　　In very remote areas, or where the terrain is totally unsuitable for the

6、classic survey methods of triangulation and traverse, there is, however, a need for direct position determination. For the majority of this work, visual observation to the stars has been replaced by electromagnetic measu

7、rements to or from artificial earth satellites. In addition, the relative positions of survey stations can be determined directly by inertial techniques originally developed for aircraft navigation.</p><p>　

8、　1.1 Inertial Positioning</p><p>　　A pair of gyros are incorporated in a position fixing device known as the Auto-Surveyor manufactured by Litton Systems. It has originated from an aircraft navigation syste

9、m, which was developed for military applications into its present three-dimensional survey system. ‘Hardware’ consists of (i)the inertial measuring unit, (ii)a computer ,(iii)a cassette recorder,(iv)a display and control

10、 unit and (v) the power supply .These items can be placed anywhere within a road vehicle or helicopter provi</p><p>　　The measuring unit contains a gyro-stabilized platform with two air-bearing gyroscopes i

11、n four gimbal mountings which keep its three orthogonal axis oriented in space in a north-east=downwards relationship . Each axis also has a sensor-torquer type of acclerometer which defines acceleration in the particula

12、r direction via a quantitizer system feeding the computer .This is pre-programmed to compute the survey as it is carried out and to control the system (see Fig.1)</p><p>　　Before staring the survey an alignm

13、ent drill carried out at the origin station. This is said to have a duration of about one hour (that for the survey is restricted to some four hours or so) and the platform levels itself with respect to the local vertica

14、l and aligns its nothing axis with the local meridian so that the accelerometers are in the directions of north, east and down. Simultaneously the computer monitors the biases of the system and evaluates the initial cond

15、itions for a Kalman filte</p><p>　　When the alignment is complete the known coordinates and elevation of the station are fed in by the operator and the traverse can begin. The orthogonal movements are sensed

16、 by the accelerometers and, at intervals of sixteen milliseconds, the signals to the computer are doubly integrated into distances of displacement with respect to the origin. In the Auto-Surveyor ‘z-increments’ accumulat

17、e as elevation differences, whilst the other two increments are used to compute values of geodetic latitude </p><p>　　At approximately four minute intervals the vehicle is halted a ‘zero velocity updating’ i

18、s carried out. This takes about thirty seconds and the platform is re-leveled, with respect to local vertical, and effectively resets ’vertical zero‘. As mentioned above, previous calculations and platform torquing are w

19、ith respect to the reference spheroid so that the amount of torque used for the re-leveling is a measure of the directional change of deviation from the vertical. Since the vehicle is station</p><p>　　The su

20、rvey now continues with successive updating stops and also with halts at the survey stations where the same process occurs. At the terminal station known coordinates and elevations are entered as updating information and

21、 a zero velocity update is carried out; the Kalman filter carries out a smoothing adjustment data and results of the smoothing are registered on the recorder.</p><p>　　Traverse lines are normally measured in

22、 two directions, occupying the same stations , discrepancies then indicating effects of gyrodrift on platform alignment .Standard errors of ±0.20 m in position of points at 10 km separation are achievable with a sim

23、ilar value for heighting when a road vehicle is used.</p><p>　　Ferranti manufacture a corresponding system in the UK, and reference can be made to a report in the New Civil Engineer, 17 January 1980, on its

24、value to the highway engineer. This report refers specifically to their Inertial Road Surveyor although it indicates that systems for land surveys, borehole surveys and underwater surveys are available too.</p>&l

25、t;p>　　2 GPS IN NAVIGATIONAL APPLICATIONS </p><p>　　2.1 INTRODUCTION </p><p>　　Global Positioning System (GPS) has for several years been a buzzword for professionals in many fields includin

26、g surveying, geodesy, GIS, meteorology, and geodynamics. The reason for this GPS wonder perhaps lies in the superior capability of GPS: it offers solutions to many problems that we could not or felt difficult to solve, a

27、nd also enables us to do many things better than before. Navigation is one of these things, which has been greatly changed from the development of GPS.</p><p>　　This paper will provide an overview of GPS as

28、applied to navigation. It will first describe briefly the principles of GPS .The different GPS based positioning methods in navigation will then be discussed, followed by an review of GPS based systems for air, land and

29、marine navigation.</p><p>　　2.2 PRINCIPLES OF GPS POSITIONING</p><p>　　GPS is a satellite based passive positioning system that was initially designed primarily for military use .It was develop

30、ed and has been maintained by the United States Department of Defense (US DoD). The system is now used by both the military and civilian users to obtain high accuracy position, velocity and time information, 24 hours a d

31、ay, under all weather conditions, and anywhere in the world. The system was 1993 and full operational capability (FOC) in April 1995.</p><p>　　2.2.1 The Components of GPS</p><p>　　One common wa

32、y to look at GPS is to resolve it into three segments:</p><p>　　The space segment refers to GPS satellites that are orbiting at an altitude of about 20,200 km above the earth surface. The full operational ca

33、pacity of GPS is achieved with 24 active satellites. There are currently 27 operational satellites, three of that are the active spares that can be used as replacements when the active satellites are out of services. The

34、 key components in satellite are the antennas sending and receiving signals, two large wings covered with solar cells to generate power f</p><p>　　The control segment consists of 5 monitor stations, 3 ground

35、 antennas, and 1 master control station. The monitor stations passively track all satellites in view, accumulating ranging data. The tracked data are processed at the master control station to determine satellite orbits

36、and to update each satellite’s Navigation Message. The updated information is transmitted to each satellite via the ground antennas.</p><p>　　The user segment is anybody who has a GPS receiver. The surveyors

37、, the navigators and the GIS data collectors are examples of the users.</p><p>　　The signals that GPS satellites send out consist of two codes, the coarse acquisition (C/A) code and the precise (P) code, and

38、 a Navigation Message. The GPS codes are just like a series of 1’s and 0’s that are arranged into certain sequences, Figure 1. The C/A code is used for the standard positioning service (SPS) available to all users. The s

39、ervice offers a positional accuracy of about 100 m horizontally and 156 m vertically at the 95% probability level. The P code is used for the Precise Posi</p><p>　　The GPS Navigation Message contains such in

40、formation as the orbital elements of the satellites, clock behavior, and an almanac that gives the approximate data for each active satellite. Two carrier frequencies on L-band, L1 and L2 are used to carry the signals de

41、scribed above. L1 has a wave-length of about 19 cm (1575.42MHz) and L2 a wave-length of about 24 cm (1227.60MHz). Both L1 and L2 are microwave frequencies and can penetrate the atmosphere. L1 carries both the C/A and the

42、 p codes and L2 t</p><p>　　To the more sophisticated users such as the surveyors, positioning using the code information cannot fulfill their accuracy requirements, say at the centimeter or millimeter level.

43、 In this case, the L1 or L2, or both L1 and L2 carrier phases are also observed and used for positioning.</p><p>　　2.2.2 The Working Principles of GPS </p><p>　　GPS measures positions by measur

44、ing distances. GPS satellites have known orbits and therefore known positions at any instant time. Therefore, if the distances to three or more GPS satellites can be measured from a point anywhere on near the earth surfa

45、ce, the three-dimensional position of the point can bi calculated, Figure 2.</p><p>　　The distances between the point and the satellites are determined either using the code or the carrier phase observations

46、. The same GPS codes are generated at the same time by both the satellites and the GPS receiver. When the receiver receives the code information from the satellites, it correlates the signals it generates and those recei

47、ved from the satellites, Figure 3, which can determine the time that takes for the GPS signal to travel from a satellite to the receiver. The time can then be </p><p>　　Figure3. Time measurement by code corr

48、elation</p><p>　　Figure4. Carrier waves and phase measurement</p><p>　　As the clock of the receiver has usually a much lower accuracy than those on a GPS satellite, the clock time is in practice

49、 commonly considered as an unknown parameter which is solved together with the position of the receiver point. In this case, signals from at least four GPS satellites are required, as there are four unknown values to be

50、solves for.</p><p>　　When carrier phase observations are used in GPS positioning, the distance between a receiver point and a satellite is determined using.</p><p>　　Distance = (1)&

51、lt;/p><p>　　Where is the wavelength of the carrier wave; N is the whole wave numbers counted from a satellite to the receiver and is the length that is shorter than one wavelength, Figure4. is determined dir

52、ectly from the phase measurements. N is the integer ambiguity and is usually solved for based on continuous phase observations over some extended time.</p><p>　　2.2.3 Pros and Cons of GPS </p><p&

53、gt;　　Some general points on the advantages of GPS are given here only. First, it covers the whole globe spatially. Hence the word ‘Global’ in is its name, and continuously in time for 24 hour a day. Second, the system of

54、fers high positioning accuracy at an affordable price to the user. Besides, GPS is convenient to use in many applications.</p><p>　　GPS also has its disadvantages. Perhaps the biggest problem that it has is

55、the requirement of line of sight to GPS satellites. GPS signals can penetrate the atmosphere but not any solid objects such as buildings, trees, and mountains. This requirement seriously limits the use as buildings, tree

56、s, and mountains. This requirement seriously limits the use of GPS in environments such as dense urban areas and underground. Another problem with GPS is the multipath effects that contribute to significan</p><

57、;p>　　3 GPS BASED POSITIONING METHODS IN NAVIGATION </p><p>　　GPS was designed primarily as a tool for navigation. It has been successfully applied for the navigation of vehicles such as cars, ships an

58、d airplanes, as well as for the guidance of weaponry objects such as missiles. This section will look at the different positioning methods of using GPS in navigation.</p><p>　　3.1 Single Receiver Positionin

59、g</p><p>　　The simplest way to used GPS for navigation is to carry a GPS receiver whenever you go. The receiver can offer in real-time the SPS positioning accuracy, that was discussed earlier, as long as sig

60、nals from four or more GPS satellites can be received. Since such an application is very basic, almost any commercial GPS receivers on the market can be used for this purpose. Many of the receiver units cost less than US

61、$100. This simple GPS positioning method is used very commonly for recreational acti</p><p>　　3.2 Differential GPS (DGPS) Positioning</p><p>　　If the positioning accuracy described above is ins

62、ufficient, an easy and affective way to increase the accuracy is to use differential GPS. In this operation mode, two GPS receivers are required, and the other carried around to where the position needs to be determined.

63、 In this case, the first receiver is called the reference station and the second the roving station.</p><p>　　If the user is close enough to the reference station, various GPS errors, such as the effect of t

64、he atmosphere, are very similar for both of the two stations. The reference station can be used to determine the errors in the three coordinate components. Corrections can be worked out for the position of the roving sta

65、tion based on the errors determined at the reference station. The positioning accuracy can be greatly improved by doing this ‘differential’ operation. DGPS technique has been repeated</p><p>　　If real-time p

66、ositioning is required, a data communication link between the two stations is required. A common approach is to use a pair of radios if the distance between the two stations is short, say within a few kilometers. For dis

67、tances up to a few hundred kilometers, a broadcasting station can also be used to send the correction messages to the entire designated area. For example, Hong Kong has established a permanent GPS reference station on it

68、s Kau Yi Chau island. A transmitter is used to</p><p>　　The simple differential operation described above has relatively limited coverage, and is restricted by the coverage of the terrestrial communication s

69、ystem. Besides, the positioning accuracy decreases as the separation communication system. Besides, the positioning accuracy decreases as the separation between the user and the reference station increases. A technique c

70、alled Wide Area Differential GPS (WADGPS) can be used to overcome the problems of the simple differential method. WADGPS uses a n</p><p>　　3.3 GPS Aided with Additional Sensors and Information </p>

71、<p>　　As said above, the requirement of direct line of sigh to GPS satellites makes it very difficult to use GPS in restricted areas such as high rise cities. For example, recent tests have shown that only about 30

72、percent of Hong Kong can receive signals from four or more GPS satellites. One way to solve the problem is to aid GPS with sensors such as compasses, odometers, inertial navigation systems (INS), which basically use gyro

73、s and accelerometers to the determination of positions, or additional i</p><p>　　Pseudolite, a pseudo-satellite as its name implies, is a device that can transmit GPS-like signals, A pseudolite can be placed

74、 at strategic locations such as on a tall building at a road intersection to transmit signals to nearby areas. The signals form a pseudolite can be treated in the same way as those from a real satellite.</p><p

75、>　　GPS can also be used in combination with GLONASS (Global Navigation Satellite System), a system developed and maintained by Russia. The design and working principles of GLONASS are to certain extent similar to GPS.

76、 Efforts have been made by both researchers and instrument manufacturers to integrate the two systems to achieve better positioning accuracy and especially better satellite coverage in difficult environments. Receivers c

77、apable of receiving signals from both GPS and GLONASS satellites h</p><p>　　The system integrity and future continuity of GLONASS has always been a concern, especially when the number of GLONASS satellites i

78、n space has dropped dramatically in 1997-1998.</p><p>　　The accuracy of differential GPS+GLONASS has been reported to be better than 0.5m</p><p>　　4 GPS BASED NAVIGATION SYSTEMS</p><

79、p>　　Various GPS based navigation systems have been developed. This section will take a brief look at these and the basic requirements for land, air and marine navigation. </p><p>　　4.1 Airplane Navigatio

80、n </p><p>　　It is understandable that navigation has different requirements under different circumstances. There are however some general considerations when designing different navigation systems, which are

81、 the accuracy, availability, continuity and integrity of the systems.</p><p>　　Although GPS and GLONASS combined provide very good positioning capability, they still however, when used alone, cannot meet the

82、 criteria as a sole means for navigation in aircraft navigation and landing guidance, or for safety-critical use in the marine and land environment. To meet these requirements, the GNSS-1 and GNSS-2(GNSS also comes from

83、Global Navigation Satellite System) have been proposed. GNSS-1 is a satellite navigation system having GPS and/or GLONASS as backbone, augmented by othe</p><p>　　The following are some of the developments in

84、 the scope of GNSS-1:</p><p>　　European Geostationary Navigation Overlay Service (EGNOS)</p><p>　　In Europe, a Tri-Partite Group made up of the European Organization for the Safety of Air Naviga

85、tion (EUROCONTROL), the European Space Agency (ESA) and the European Commission (EC) jointly manages the EGNOS. The EC is responsible for institutional and policy issues and funding. EUROCONTROL defines the user requirem

86、ents and is also involved in the test and validation phase of the system development. ESA manages the development of EGNOS within GNSS-1.</p><p>　　The coverage of EGNOS will be the footprint of Inmarsat Atla

87、ntic Ocean Regions East (AORE) and Indian Ocean Regions (IOR) as EGNOS uses these satellites as core transponder of the system. EGNOS is planned to reach its Initial Operational Capability, (IOC) in 1999and Final Operati

88、onal Capability (FOC) in 2001. FOC is intended to meet sole-means requirements for en-route to Cat-I.</p><p>　　EGNOS will include GPS/GLONASS. GPS-like ranging system, wide area differential systems, ranging

89、 and integrity monitoring stations (RIMS), and geostationary integrity channel. When the Final Operational Capability (FOC) is declared the use of GPS/(GLONASS)/EGNOS/RAIM(Receiver Autonomous Integrity Monitoring) as sol

90、e means of navigation for up to Cat-I service shall be reached.</p><p>　　Wide Area Augmentation System (WAAS) </p><p>　　WAAS has been developed by the US Federal Aviation Administration (FAA). T

91、he ground network of the system includes 25 reference stations and 2 master stations providing differential and ionospheric corrections for improved accuracy. To achieve the various requirements of all phases of flight u

92、p to Cat-I, WAAS will also broadcast integrity messages and additional GPS-like signal, beside the GPS differential corrections. The initial supplemental service, phase I of the system, has been scheduled f</p>&l

93、t;p>　　The WAAS aims at providing service for precise up to Cat-I. Local Area Augmentation Sys-tern(LAAS), which is similar in principle to WAAS but with a smaller area of coverage and higher positioning accuracy, will

94、 be employed for more stringent requirements of Cat-II/III precise approaches.</p><p>　　MTSAT Satellite Based Augmentation System (MSAS).</p><p>　　The Japanese Multi-functional Transport Satelli

95、te (MTSAT) Satellite Based Augmentation System (MSAS) is developed by the Japan Civil Aviation Bureau (JCAB) to support sole means navigation services for en-route to precision approach phases of flight. The first MTSAT

96、is scheduled to be launched in 1999. Initial phase I (Cat-I) of the system is to be completed by 2001 and the final MSAS capability (CAT-II/III) is scheduled at 2005.</p><p>　　MASA in designed to provide Air

97、 Traffic (ATS) and meteorological mission. The system configuration is similar to the US WAAS. Consisting of ground network for broadcasting integrity and correction data and to provide additional GPS-like ranging system

98、 from geostationary satellite for improving availability and continuity.</p><p>　　The development of GNSS-2 has to consider institutional issues regarding the ownership, control and interoperability of the s

99、ystems. With the consent of the ICAO (International Civil Aviation Organization) members, an interoperability working group has been set up and held its first meeting on July 1998 to discuss these issues. The interoperab