GPS ve GPS'in alımlarında kullanılması /
Yazar: SERVET YAPRAK
Danışman: DOÇ. DR. ERSOY ARSLAN
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Jeodezi ve Fotogrametri Mühendisliği Ana Bilim Dalı / Jeodezi ve Fotogrametri Bilim Dalı
Derece: Yüksek Lisans, 1998
Konu: Jeodezi ve Fotogrametri = Geodesy and Photogrammetry
Dizin: GPS = Global Positioning System

Özet:
Bu tezde GPS'in teorisi anlatılmakta ve detay ölçmelerinde GPS Dur ve Git yöntemi ile takeometrik alım yöntemi karşılaştırılmaktadır. Bu amaçla uygulama arazisi olarak İTÜ Maslak Kampusu seçilmiştir. Uygulama arazisinde transformasyon işleminde kullanılmak üzere ülke koordinat sisteminde koordinatları bilinen 5 adet poligon noktası (003, 010, 039, 101, 102) ayrıca WGS sisteminde koordinatları bilinen itay noktaları ana ağ olarak alınmıştır. Bu noktalarda statik GPS ölçmeleri yapılmıştır. Arazinin takeometrik olarak ölçülmesi için de 101 ve 003 nolu poligon noktalarına dayanan 7 noktalı poligon ağı tesis edilmiştir. Yöntemlerin karşılaştırılmasında esas alınmak üzere özellikle kaldırım kenarlarında yaklaşık 450 nokta yağlı boya ile işaretlenmiş ve bu noktalar her iki yöntemle ölçülmüştür. Buna ilave olarak Prof. Mustafa İnan Kütüphanesi ile Prof. Bedri KARAFAKİOĞLU caddesi arasındaki alan her iki yöntemle topoğrafik yapıyı yansıtacak şekilde ölçülmüştür. Sonuç olarak takeometrik alım yöntemi ile 579 adet, Dur ve Git yöntemi ile ise 513 nokta ölçülmüş ve ülke koordinat sisteminde koordinatları hesaplanmıştır. Eşlenik olarak alınan noktalardan 437 tanesinin koordinat farkları hesaplan mış ve sonuçlar diskette verilmiştir. Ayrıca her iki yöntemle ölçülen arazinin 1/1000 ölçekli haritaları çizilmiş ve diskette verilmiştir. İki yöntem karşılaştırıldığında 437 noktada minimum, maksimum ve ortala ma koordinat farkları aşağıda gösterildiği gibi bulunmuştur. Zaman açısından, GPS ölçülerinde %47'lik bir zaman tasarrufu sözkonusudur. Bununla birlikte bina alımlarında ve yoğun ağaçların bulunduğu bölgelerde Dur ve Git yöntemi ile ölçü yapmanın olanaksız olduğu görülmüştür.

Abstract:
Since the dawn of civilization, men have looked to the heavens with awe searching for portentous signs. Some of these persons became experts and developed rules to govern life. These men were the first surveyors. The chain of technical developments from this early astronomical surveyors to the present satellite geodesists reflects men's desire to able to master time and space to use science to further his society. The surveyor's role in society has remained unchanged from the early days; this role is to determine land boundaries, provide maps, and control the construction of public works. The immediate predecessor of today's modern positioning system is the Navy Satellite System (NNSS), also called transit system transit system was developed by US Military Service to determine the positions' of vessels and aircraft. Civilian use of this system was authorized and today TRANSIT satellites are being used by to determine the coordinates of selected datum points. Global Positioning System was used to replace the TRANSIT system. The main problem with TRANSIT system was large time gaps in coverage. The second problem is the long navigation accuracy. In contrast, GPS gives exact answers to these questions " What time, What question, What velocity is it?" quickly, accurately and inexpensively anywhere on the globe at any time. 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 will be continuously available on a world-wide bases and is independent of meteorological conditions. GPS has been under development in the USA since 1973. It has been used for the solution of geodetic problems since 1983. The system consist of 24 satellite pleased in orbits of about 20.200 km. altitude abovethe earth surface. The final arrangement of satellite is planned in such a way that at least four satellites are simultaneously visible above the horizon anywhere on the earth 24 hours a day. GPS has three segments. These segments are space, control and user. Space segment comprises satellites. Each GPS satellite transmits two radio signals : Link One (L1) and Link Two (L2). The L1 signal is broadcast at a frequency of 1575.42 MHz., and the L2 at 1227.60 MHz. The L1 carrier has wave length of 19 cm.; the L2 carrier about 24 cm. The number of complete carrier wave lengths from the satellite to receiver is called the integer. The main' operational tasks of control segment are: tracing of satellites for orbit and clock determination, prediction modeling, time synchronization of satellites and upload of data message to the satellites. There are two kinds of users these are military user and civilian user. Both user perform every kind of surveying modes. Civilian users use the system to produce all kinds of maps. X L2 SATELLITE MESSAGE ( P CODE 1 ( P CODE 1 [ C/A.CODEİ { RECEIVER)* COMPUTER DATA REDUCTION GPS uses the one way technical ranging and the receiver clock is not synchronized with the satellite clock. This synchronization error is the reason for the term " pseudorange ". The pseudorange is either derived from measuring the travel timeof signal and multiplying it by its velocity or by measuring the phase of signal. The pseudorange equations comprise four unknowns : The desired points three coordinates and the clock error. Four satellites are necessary to solve four unknowns. The solution becomes more complicated when using measured phase. This observable is ambiguous by an integer number of signal wave lengths so that the model four phase pseudoranges is augmented by an initial bias called integer ambiguity. The code pseudoranges and phase pseudoranges are affected by both, systematic errors or biases and random noise. Systematic effects can be modelled and give rise to additional terms in the observation equations and eliminated by appropriate combinations of the observable. Differencing between receivers eliminates satellite specific biases. Double differenced pseudoranges are, to high degree, free of systematic errors originating from satellites and receivers. Ionospheric refraction can be virtually eliminated by an adequate combinations of the dual frequency data. Phase differencing means subtracting one equation from another. There are three kinds of phase differencing: Between receiver, between satellite and between epoch. The most popular one is between receiver differencing. The geometry of visible satellites is an important factor in achieving high quality results. The geometry changes with time due to the relative motion of satellites. A measure of the geometry is the Dilution of Precision (DOP) factor. The DOP factor is based on the volume of a geometric figure where the apex is the ground observing station and the sides are the vectors from this station to each satellite. If the ground station is observing three satellites, the geometric figure is a tetra hedron; with four satellites the figure is an inverted pyramid. The larger the volume of this figure, the better the satellite geometry. The DOP is the reciprocal value of the volume^ of the figure; the larger the volume, the lower the value of DOP. There are four different DOP designations : 1- Position Dilution of Precision (PDOP) 2- Horizontal dilution of Precision (HDOP)3- Vertical Dilution of Precision (VDOP) 4- Time Dilution of Precision (TDOP) Various technical have been developed in recent years that exploit the capability of GPS to provide precise coordinates after a very short observation time or even while the receiver is moving along a trajectory, Static method : Static surveying is the traditional method for measuring GPS baselines. With this method, two or more receivers will occupy survey stations for 30-60 minutes. Static survey remains the most accurate method of working with GPS. Short Static Method ; Short static is a calculation method which allows a reduction in the station occupation time. The method can be used with single or dual frequency data. Provided that the receiver data contains accurate carrier phase and pseudorange data. The method is very similar to static except that the occupation time can be 5-30 minutes. The time depends on the satellite geometry, number of satellites. And other factors such as multipath. Kinematic Method : The kinematic survey method relies on the receiver constantly recording data from at least four satellites during the entire survey including when moving between stations. The results can be shown as continuous were the surveyor is interested in a continuous stream of coordinates or as Stop and Go, were the surveyor is only interested in a coordinate for each stop point, that is whenever he was stationary. The method has the same accuracy as conventional tacheometry with a point occupation time of a few seconds. Preplanning is necessary to overcome site obstraction, avoid possible loss of lock, and observe as many points as possible during the day. In this thesis, the theory of GPS was explained and then in great detail, the efficiency of classical takeometric method and the GPS Stop and Go method were compared. For this reason, the Maslak campus of ITU was chosen as an application site. For using the transformation process, well-known four polygon point in the national coordinate system and well-known itay point in WGS84 system as a main network were selected. The static GPS measurements wer made at the so-called points. Formeasuring the site as a takeometric, the polygon network with seven points were established. At the. comparing the methods, as a reference, the 450 points on the pavement sides especially were labelled by means of paint and then these points were measured by using the both methods. In addition to these, the area between the Prof. B. Karafakioğlu street and the Prof Mustafa İnan library were measured freely so as to reflect the topographic structure. Finally, the 579 points acquired from the takeometric method and the 513 points acquired from the Stop and Go method were measured and then their coordinates were calculated at the national coordinate system. The coordinate differences of 437 points, simultaneously used both methods, were calculated and the results obtained were listed in the form of tables. The maximum, minimum and mean coordinate differences stemmed from comparing the both methods each other obtained as follows: In GPS measuring process, the time saving was attained as 47 %. However, as seen at the maps, it was seen that the use of Stop and Go method in the areas consisting of so many trees and in the having buildings was impossible