M. Tevfik ÖZLÜDEMİR, Tevfik AYAN

GPS ile konum belirlemede stokastik modellerin etkileri

GPS ölçmelerindeki en önemli hata kaynakları multipath etkisi ve gecikme etkisidir. Son yıllarda bu hataları en aza indirme amacıyla yapılan araştırmalar ağırlıklı olarak, yeni troposferik gecikme modellerin üretilmesi, multipath etkisinin modellenmesi ve yeni stokastik modellerin geliştirilmesi üzerinde yoğunlaşmıştır. Bu çalışmada sinyal kalitesine dayalı bir stokastik model ve bu modelin nokta konumlarının belirlenmesi üzerindeki etkileri incelenmektedir. Temel sinyal kalitesi ölçütü olan sinyal-noise oranına dayalı olan bu model GPS ölçüleri üzerinde uygulanmış ve geleneksel eş-ağırlıklı değerlendirme modeli ile karşılaştırmalı olarak analiz edilmiştir. Bu modelin uygulanmasıyla daha iyi koordinat çözümleri elde edilmiştir. Sarnıçlar, ayrıca multipath etkisinin birbirini izleyen günlerdeki tekrarlanabilirliğini ortaya koymaktadır.

Effects of stochastic models in GPS positioning

The most important error sources in GPS measurements are the multipath effect, taking place when the electromagnetic wave reflects from the reflecting surfaces around the receiver, and the delay effect that occurs during the propagation of the wave through the troposphere because of the refraction effect. In recent years, many scientists have been doing research for minimising the effects of these error sources. These researches mainly focus on the development of the mapping functions produced for modelling the tropospheric delay with respect to the meteorological data or mathematical methods, modelling of the multipath effect and development of new stochastic or weighting models, which enable us to process the low elevated GPS observations too. In this study a signal quality based stochastic model and its impact on the point positioning are investigated. This model is the Sigma-$varepsilon$ model, which is based on the signal-to-noise ratio, which is the basic signal quality measure. This model has been applied on some GPS measurements. It has been shown that through the application of this model better coordinate solutions are obtained. The results also show that this model characterises the day-to-day repeatability of the multipath effect.

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