GPS ölçmelerinin planlanması ve ağ tasarımı

Başlık çevirisi mevcut değil.

Tez No: 75577
Yazar: ERSOY ARSLAN
Danışmanlar: DOÇ. DR. ERSOY ASLAN
Tez Türü: Yüksek Lisans
Konular: Jeodezi ve Fotogrametri, Geodesy and Photogrammetry
Anahtar Kelimeler: Belirtilmemiş.
Yıl: 1998
Dil: Türkçe
Üniversite: İstanbul Teknik Üniversitesi
Enstitü: Fen Bilimleri Enstitüsü
Ana Bilim Dalı: Jeodezi ve Fotogrametri Mühendisliği Ana Bilim Dalı
Bilim Dalı: Belirtilmemiş.
Sayfa Sayısı: 140

Özet

ÖZET GPS uydu sistemi, dünyanın herhangi bir yerinde, günün her saatinde ve her atmosferik koşulda duyarlı olarak konum belirleyen bir sistemdir. GPS sınırlı olarak sivil kullanıma açılmasıyla, sistem jeodezi alanında çok geniş bir kullanım alanı bulmuştur. Jeodezik ölçme çalışmaları genellikle statik relatif konum belirleme yöntemiyle gerçekleştirilir. Statik ölçme yönteminde alıcılar istasyon noktasında sabit kalırken uydudan gelen verileri alırlar. İstenilen nokta konum doğruluğuna göre statik, hızlı statik, dur-git yöntemleri kullanılabilir. Relatif konum belirlemede pseudorange ve taşıyıcı faz ölçmelerinden biri kullanılabilir. En duyarlı sonuçlar taşıyıcı faz ölçmeleri ile elde edilir. Taşıyıcı faz ölçmelerini değerlendirmek için faz ölçmelerinin lineer kombinasyonları veya farksız yöntemler uygulanır. GPS yazılımlarında tek baz veya çoklu baz değerlendirmeleri kullanılabilir. Çoklu baz belirlemede, veriler bir gözlem oturumu veya çok istasyonlu- çoklu oturum için değerlendirilebilir. Bunun yapılabilmesi için oturumlar arasında ortak istasyonlar olması gerekir. Günümüzde GPS uygulamaları duyarlılığı, hızı ve ekonomikliği ile haritacılıkta önemli bir yer almıştır. GPS ile ağ ölçmelerinde, eldeki alıcı sayısına, eleman sayısına ve arazinin yapısına göre uygun yöntem seçilmelidir. Bu nedenle ağ ölçmelerinde istenilen sonuçlara ulaşmak için dikkatli planlama yapılmasına özen gösterilmelidir. GPS jeodezik ağ ölçmeleri gerçekleştirilmeden önce ağ iyi analiz edilmeli ve nasıl bir ölçme dizaynı izleneceğine karar verilmelidir. Bu çalışmada GPS ölçmelerinin planlamasının son safhası olan ağ dizaynına ağırlık verilmiştir ve ikiden fazla alıcı ile relatif statik GPS ölçmelerinin ağ dizaynı stratejilerine bazı örnekler verilmiştir. Bölüml'de GPS hakkında genel bilgiler, Bölüm2'de GPS ölçmeleri ve matematiksel modelleri konularına değinilmiştir. Bölüm3'te GPS ölçmelerinin planlanması anlatılmıştır ve Bölüm4'te jeodezik GPS kontrol ağları için eldeki alıcı sayısına göre nasıl bir ölçme dizaynı izleneceği konusu incelenmiştir. Son olarak Bölüm5'te uygulama kısmına yer verilmiştir ve İ.T.Ü tarafından gerçekleştirilen 1996 Zonguldak GPS Ağı Projesinin ana ağı farklı şekillerde dizayn edilerek ölçüler SK.I yazılımı ile değerlendirilmiş ve sonuçların doğrulukları ilk ana ağ değerlendirmesiyle karşılaştırılmıştır. vıtı

Özet (Çeviri)

PLANNING OF GPS MEASUREMENTS AND NETWORK DESIGN SUMMARY The NAVSTAR GPS (Navigation System with Time and Ranging Global Positioning System) is a satellite-based radio navigation system providing precise three- dimensional position, navigation and time information to suitably equipped users. The system is now continuously available on a world-wide basis, and is independent of meteorological conditions. GPS provides the three- dimensional positions of the ground points quickly, accurately and inexpensively anywhere on the globe at any time, thus system has found a great working area for the solution of geodetic problems. GPS is primarily a navigation system. The fundamental navigation principle is based on the measurement of so-called pseudoranges between the user and four satellites. Starting from the known satellite coordinates in a suitable reference frame, the coordinates of the user antenna can be determined. From the geometrical point of view three range measurements are sufficient, a fourth observation is necessary because of the clock synchronisation error. GPS has three segments. These are space, control and user. Space segment comprises satellites. The satellites are 20200 km. above the earth and have 12 hours orbital periods. Each satellite transmits signals on both LI, L2 carrier frequencies. These are the navigation signals(codes), navigation and system data(message). The tasks of the control segment are to monitor and control the satellite system continuously, determine the GPS system time, predict the satellite ephemerides and the behaviour of the satellite clocks, update periodically the navigation message for each particular satellite. Belonging to the control segment are the Master Control Station, several monitor stations located around the world and ground antennas for uploading data into the satellites. GPS receivers can be classified into three main groups. These are C/A-code pseudorange, C/A-code carrier phase and P-code carrier phase measurement instruments. The Global Positioning System is becoming very important in geodesy, land surveying, cadastral surveying and engineering. The practical aspects of planning and implementing a GPS satellite survey are as important as the sophisticated instrumentation and methodology employed in GPS surveys. To obtain the desired results of a GPS survey, careful planning, effective specifications, established field and office procedures must be employed. GPS planning can be divided into these steps:. Project definition and objectives. Tolerances and error sources. Pre-planning. Observational procedures. Post processing IXGPS projects may include monumentation and observations or only observations to provide three dimensional coordinates on an already monumented control network. Although intervisibility between stations is not necessary in a GPS survey, visibility between satellite and receiver station is necessary to obtain continuous observation of satellite signals. Buildings, trees, power lines, telephone lines, microwave antennas, etc., may cause cycle slips and multipath contamination. The ultimate objective of a GPS survey is accurate positioning of points on the earth. The accuracy of the positioning depends upon the project definition, purpose, and use of three- dimensional coordinates to achieve certain goals. Error sources and tolerance limits along with hardware and software availability should be studied throughly before implementing any GPS project. The main sources of errors in GPS surveying are orbit perturbation, relativity, tropospheric and stratospheric refraction, multipath interference, ionospheric dispersion, conversion of GPS(ellipsoidal) heights to orthometric heights, instruments limitation, instrument setup and antenna height measurements. Assuming that the standard deviations produced by these error factors are uncorrelated, the total a priori standard deviation can be computed as: Ot=[a Orf> + Of Relat + O Trop + O- M + O- Ion + O last] ' (1) The total a priori standard deviation should always be less than the tolerance limits. Before starting a GPS project implementation, the following factors should be carefully checked so that the GPS survey meets the accuracy standards required:. maximum number of horizontal and vertical control points required are available for the project maximum and minimum station spacing location of network control points requirement for direct connection between already existing control points types of receivers to be used number of receivers observing simultaneously satellites to be observed period of observation sessions independent occupation per station repeat base line measurements fiducial or master stations required requirement for observation of meteorological data antenna types and setup Depending upon the number of receivers used in any GPS project, the observational mode could be a single base line (two receivers) or network mode (more than two receivers) of observation. For many geodetic GPS projects a network observation mode would be better than a single base line observational procedure. The final part of the GPS project planning and implementation is the post processing stage. The GPS survey would not be very accurate and precise without this stage. The data areprocessed using least squares techniques in double difference (fixed and float) and triple difference mode. Triple difference processing requires almost no interaction and gives more precise results for long base lines. In general, these steps are followed to process the GPS data:. Each vector of the GPS project is computed in terms of X, Y, Z coordinate differences between points. Least-squares solution for each vector is computed. Loop closure is performed to isolate bad lines. The base line vectors are adjusted again with three-dimensional adjustment programs to yield information for the final quality control checks such as absolute positional accuracy, error ellipse, etc.. Datum transformation or computation of coordinates in a projection plane is performed In this study, the network design strategies which is necessary for successful completion of the GPS geodetic projects are explained and some examples for network designs are given. Network observation design of the GPS geodetic projects is the final part of the planning of GPS surveys. Today, the operation of GPS receivers no longer requires highly qualified survey personnel, but the long of observation sessions, the number of receivers and the motions of them from point to point are important for the completion of GPS project campaigns fastly and economically and to achieve the results accurately. GPS geodetic network measurements are implemented by using the relative techniques. The essential strength of relative techniques lies in the fact that a part of the error influences at neighbouring stations is strongly correlated and is thee for cancelled out when a difference is taken. This is especially true of orbit errors, errors of the satellite clock and errors in the ionospheric modelling. An accuracy increase by a factor 103 to 104 is brought about in the geodetic relative mode with at least two simultaneously operating receivers, as compared with the single receiver mode. All observations made simultaneously during a given time period in the course of a GPS project are called a session. Each session has to be connected to at least one other session of the network through one or more identical stations where observations have been carried out in both sessions. An increasing number of identical stations increases the stability, the accuracy, and reliability of the total network. When three or more receivers are used in a multi session project, the design of an observation plan becomes an optimisation problem between economy, accuracy and reliability. The minimum number n of sessions in a network with s stations and using r receivers is given by: n=(s-o)/(r-o) (2) where o denotes the number of overlapping stations between sessions. In the case of a real number, n must be rounded to the next higher integer. XIAs regards logistic and practical limitations, the choice of an observation strategy will often be guided by experience, with formal optimisation criteria providing valuable aid. Since the accuracy of a local or regional GPS network is nearly independent of the station distance, the design aspects are mainly governed by logistic, economic, and reliability factors. Some general rules from experience are. each station should be occupied at least twice under different conditions to identify blunders. neighbouring stations should be occupied simultaneously because the ambiguity resolution works best over short distances. for medium-sized projects the use of 4-10 receivers is a good compromise with respect to logistics, production rate, and reliability. a certain number of baselines should be observed twice for accuracy checks. the network should consist of closed loops or other geometric figures. ties should be made at least three horizontal control points which should also be directly occupied. ties should be made to at least four vertical control points by the most direct means Besides the accuracy the reliability of a GPS network is important for network quality. Reliability means the ability of a network to self-check against blunders or systematic errors. In section 1, the general concept of GPS system are summarised. In section 2, GPS observables which consists the subjects about observation methods, biased and random errors of GPS measurements, and mathematical models for relative positioning(single, double, triple differences) are explained. And some definitions about the GPS observations are given to make remember. In section 3, planning of GPS observations are mentioned. And this section consists of evaluation of a priori variances to check whether the project can be performed within the given tolerances, field reconnaissance, monumentation, network design with an example, field scheduling, and post processing of the data. In section 4, observational design problem of GPS relative network positioning is widely discussed. Depending on the number of receivers, the objective of the project, the distribution of points and the accuracy required, how to decide to use the receivers in each session for implementing the campaign in optimal time is explained and a few fictitious network design figures is given as suggestion. The organisational design tables of the networks is also given. The network design also depends upon the type of the network. There are two basic types of GPS networks : (1) radial, and (2) closed geometric figures. Radial networks are performed by placing one receiver at a fixed site, and measuring base lines from this fixed site to receivers placed at other locations. Closed networks are performed by forming triangles or quadrangles in the whole network, thus the measurements will provide the accuracy control and it will be possible to adjust the base line measurements of the network. xuSection 5 contains the exercises for the main network of Zonguldak 1996 GPS project which is implemented by Istanbul Technical University. In this section the main network of the project which consists of 14 points is processed and adjusted in different configurations. The observation datas of the main network are transformed to BINEX format and processed by using SKI software program. First, all the points are processed by the single point processing. The coordinate components of point 4 are held fixed. By selecting the baseline processing mode, all the base lines are processed one by one. Then the network adjustment is computed by using all the measured base lines. In the end of the adjustment computation, outliers were noticed in (693-25), (631-25), (726-25) and (676-693) base lines. And these baselines were taken out of the network. However taking out of the base lines (693-25) and (631- 25) have not changed the configuration of the network, because they are repeated base lines. But the other two base lines caused a little change in the configuration. Then the adjustment has been repeated and reached to an acceptable result. This first network which contains almost the whole base line measurements is taken reference, the other eight networks which has different configurations for the same 14 points were adjusted and compared with the solutions of the first network. The number of the base lines taken into account in the other networks are less than the number of the base lines in the first network. However it is noticed that the coordinate results of the other networks are rather closed to the results of the first network. The projection coordinate differences of the same points for the first and the other networks are illustrated in tables in Section 5. X1U

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