PPP ve IGS Gerçek Zaman Servisi ile Su Buharı Hareketlerinin İzlenmesi

Bu çalışmada; Uluslararası Küresel Navigasyon ve Uydu Sistemleri (Global Navigation Satellite Systems - GNSS) Servisi (International GNSS Service - IGS) bünyesinde hizmet veren Gerçek Zaman Servisi (Real Time Service - RTS) aracılığıyla sağlanan uydu yörünge ve saat düzeltmelerini kullanan Gerçek Zamanlı Hassas Konum Belirleme (Real Time Precise Point Positioning – RT PPP) oturumlarının, atmosferdeki su buharı hareketlerini izlemek için yeterli hassasiyette sahip olup olmadığı araştırılmıştır. Bu amaçla, 5 IGS istasyonuna ait gözlemler ve IGS RTS düzeltmeleri kullanılarak troposferde modellenmesi zor zenit ıslak gecikmesi (Zenith Wet Delay - ZWD) değerleri gerçek zamanlı kestirilmiştir. Kestirimlerden türetilen yoğuşabilir su buharı (Precipitable Water Vapor - PWV) değerleri, aynı veya yakın konumlu Radyosonda okumaları ve aynı istasyonların art-işlem (Post Process - PP) PPP kestirimleri ile karşılaştırılmıştır. RT çözümlerde, farklı öncül troposfer modelleri ve izdüşüm fonksiyonları kullanılarak, hangi modelin kestirim sonuçlarına nasıl etki ettiği incelenmiştir. RT PPP gözlemlerinde kullanılan gerçek zamanlı uydu bilgisi ürünlerinin, atmosferi modellemek ve su buharı hareketlerini izlemek için IGS Ultra-Rapid (URP - kestirilen) ürünlere göre daha hassas sonuçlar verdiği görülmüştür. RT PPP çözümlerinde, Viyana İzdüşüm Fonksiyonu1 (Vienna Mapping Function1 – VMF1) gibi sayısal hava modellerinden türetilen troposfer model yaklaşımlarının, Küresel Basınç ve Sıcaklık / Küresel İzdüşüm Fonksiyonu (Global Pressure and Temperature - GPT / Global Mapping Function - GMF) ve New Brunswick Üniversitesi / Niell İzdüşüm Fonksiyonu (University of New Brunswick - UNB / Niell Mapping Function – NMF) gibi analitik modellere göre Radyosonda sonuçları ile daha uyumlu olduğu tespit edilmiş, PP PPP ile RT PPP oturumları arasındaki kestirim farklarının 2 mm’nin altında olduğu gözlemlenmiştir.

Monitoring Water Vapor Variations with PPP and IGS Real Time Service

In this study, the performance of Precise Point Positioning (PPP) sessions, which processing real time satellite orbit and clock corrections provided by the International GNSS Service Real Time Service (IGS RTS), were evaluated in terms of monitoring atmospheric water vapor variations. Observation data of 5 IGS stations and streamed real time correction messages were processed together in order to estimate highly spatiotemporal and hard to model variable zenith wet delay (ZWD) parameters in the real time (RT). Precipitable water vapor (PWV) values that derived from the ZWD parameters were compared with the water vapor values obtained from co-located Radiosonde readings and with the results of the post-process (PP) PPP estimates of the same IGS sites. Different a priori troposphere models and mapping functions were applied to solutions for observing their effects on the estimates. Real-time (RT) PPP campaigns, which processing real time satellite orbits and clocks, were proved to provide much more accurate estimates rather than predicted part of IGS Ultra-Rapid products (URP) during modeling the atmosphere and monitoring water vapor variations. RT PPP solutions, which using numerical weather models (NMW) derived Vienna Mapping Function 1 (VMF1) to estimate the PWV, showed better agreement with the Radiosonde readings than other RT PPP estimates processing empirical models such as Global Pressure and Temperature / Global Mapping Function (GPT / GMF) and University of New Brunswick / Niell Mapping Function (UNB / NMF). It has also been observed that differences between PP PPP and RT PPP campaigns’ estimates remain within 2 mm.

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