Öz: Küresel Navigasyon Uydu Sistemleri'nden (Global Navigation Satellite Systems, GNSS) elde edilen veriler değerlendirilirken bilimsel/akademik, ticari yazılımlar ve kullanımı gittikçe artan web tabanlı uygulamalar kullanılmaktadır. GNSS veri değerlendirme stratejisi mutlak ve bağıl olarak temelde ikiye ayrılmaktadır. Kullanımı artan web tabanlı servisler temelde mutlak yöntemi kullanan ya da bağıl yöntemi kullananlar olarak ayrılmaktadır. Hassas mutlak nokta konumlama (Precise Point Positioning, PPP) yöntemi tek bir alıcı ile cm mertebesinde konum belirlemeyi mümkün kılmakta ve kullanıcılar açısından oldukça pratik olarak konum belirleme imkânı sunmaktadır. PPP yönteminin gerçek zamanlı uygulamaları da gittikçe yaygınlaşmakta, bu durum kullanıcılar açısından hem zaman hem de maliyet tasarrufu imkânları sunmaktadır. Konum belirleme tarafında bu gelişmeler yaşanırken, ilk ortaya çıktığı günden bu yana askeri amacının yanında insanoğlunun hayatına her alanda giren Küresel Konumlama Sistemi (GPS), diğer sistemlerin de (GLONASS, BeiDou, QZSS, IRNSS vb.) devreye alınması ile oldukça yaygınlaşmıştır. Bugün artık GNSS olarak hayatımızın içinde daha fazla var olmaya devam etmektedir. Çeşitli ülkeler tarafından geliştirilen ve kullanılan uydu sistemlerinin dünya üzerine yayılmış bulunan Uluslararası GNSS Servisi (International GNSS Service, IGS) istasyonlarında veri toplanarak, konum belirleme sürecine dahil edilmesi ile The Multi-GNSS Experiment (MGEX) projesi geliştirilmiş ve belirlenen istasyonlarda, tüm uydu sistemlerinden veri toplanmasına başlanılmıştır. Bu çalışmada, web tabanlı CSRS-PPP uygulaması ile dünya üzerinde dağılmış 5 MGEX istasyonunda toplanan 10 günlük GNSS gözlem verileri değerlendirilmiştir. MGEX projesi kapsamında istasyonlardan gözlem verileri 1 saniyeden 30 saniyeye kadar gözlem aralığında ve çoklu uydu sistemlerinden (GPS, GLONASS, Galileo, QZSS, NAVIC, BeiDou, SBAS) veri toplama imkânı bulunmaktadır. CSRS-PPP uygulamasının değerlendirme stratejisinde kullandığı GPS ve GLONASS (GPS, GLONASS ve GPS+GLONASS) uydu sistemleri ile 1 ile 30 saniye aralıklı toplanmış gözlem verilerinin en az 15 dakikadan 24 saate kadar gözlem aralığında ve farklı iyonosferik koşullardaki performansı değerlendirilmiş ve yorumlanmıştır.

No abstract

<p>The evaluation of the observation data obtained from the GPS system is performed with software. The software used today is divided into academic, web-based and commercial software. Researches generally focus on academic software and web-based services that have become widespread in recent years.Commercial software is often used by daily users, mostly in classical geodesy. These softwares differ from each other; users, their purpose of use, processing methods, accuracy, users knowledge level etc. In this study, we focused commercial software’s (Topcon Magnet version 4.0.1) accuracy of GPS positioning in single and multiple base solutions.</p> <p>10 stations included in IGS network in California, USA, one base and 2, 3 and 4 network solution results in different session times (1h to 24h) positioning accuracy was achieved. In our study, it has been found that the accuracy obtained for the horizontal components North and East varies between 2 mm and 8 mm and vertical component Up varies between 3 mm and 54 mm.</p> <p>In evaluations with a reference station distance of up to 100km, increasing the number of more than 2 reference stations (3 or 4) for horizontal compenents (North and East) did not make a significant contribution to accuracy. In the case of vertical component (Up) accuracy, it is determined that accuracy is affected by interstation distance and observation time more than the number of reference stations(1, 2, 3 or 4). it was found that it was meaningful to increase the accuracy of the vertical component to be observation time for as long as possible and reference base stations to be selected from the closest possible stations. Avoidance of short observation time (1 hour and less) for all three components was found to be important in terms of accuracy to be achieved.</p> <p><strong>Keywords:</strong> Commercial software, GPS, Multiple base solution.</p>

<p>Commercial software are usually refered to in national surveying practice and local deformation studies. Since their working environment is user friendly and implementation is easy, they could be prefered by many surveying practitioners or even researchers. However their usage is usually limited to 20-30 km due mainly to their crude ambiguity resolution algorithms and  the fact that they usually use broadcast ephemeris and standard troposphere models.  Since usualy the tropospheric zenith delay is not estimated but obtained from a standard troposphere model, the accuracy of the vertical component would be affected as the height difference between baseline points grows. As the baseline length becomes >20-30 km the tropospheric error would be coupled with orbital errors. Results based on large height difference would affect positioning solutions as well as local geoid determination studies. Monitoring local deformation such as landslides would also be affected if there is large height difference between the crown and the toe. The level of baseline dependent error is usually well covered in surveying standards manual however the effect of large height difference is generally ignored. In this study, we made an attempt to quantify vertical positioning error levels both considering large height difference between baseline points and longer baseline lengths. We used the data of CORS stations in the western US for the simulation of the observing session duration. TOPCON’s software MAGNET (Ver 4.0.1) was used to process the GNSS data. It appears that every 10 km increase in the baseline length and every 100 m increase in the height difference would cause 2.59mm and 1.24 mm vertical positioning error respectively. </p>

<p>GNSS campaign measurements are often used for also volcano monitoring. The most important reason for this is that the permanent stations near the volcano are costly and likely to be damaged after the eruption. Often, even campaign measurements are risky near an active volcano. On the other hand, it would be low risky and low costly to make campaign measurements distant from volcano activities and eruptions. In this study, in order to expound the analysis results, we constituted our global test area using five IGS stations around five active volcano eruptions over 2019 via the Smithsonian Institute Global Volcanism Program. The data archives of the International GNSS service (IGS) and the time series of the Jet Propulsion Laboratory (JPL) were used for the purpose. And then we decimated the continuous data down to monthly and four monthly sampled GPS campaign time series. We also generated random values of ±3 mm for possible antenna setup errors. We tested whether the velocities obtained from monthly and four monthly solutions differ significantly from the velocities derived from daily solutions. As a result, we concluded on monthly velocities that horizontal components are compatible completely and 80% of the vertical components are compatible. We also concluded on four monthly velocities that 65% of the horizontal components are compatible and vertical components are compatible completely. We explained the utilization of campaign measurements in volcano monitoring by examining the effect of the distance between the stations and volcanoes on the results obtained.</p><p><strong>Keywords:</strong> Volcano Monitoring, GNSS Campaign Measurements.</p>