Browsing by Author "Alçay, S."

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    Availability Analysis of Gnss Orbit and Clock Files
    (TUBITAK, 2023) Öğütcü, S.; Alçay, S.; Özdemir, B.N.; Konukseven, C.; Atiz, Ö.F.
    Precise point positioning with Global Navigation Satellite Systems (GNSS), orbit and clock products are mandatory. Today, different analysis centers produce satellite orbit and clock products. At the same time, the latency of these products is divided into three different categories. In this study, the satellite availability analysis of the publicly available final, rapid and ultra-rapid orbit (sp3) and clock files were investigated for Global Positioning System (GPS), Globalnaya Navigatsionnaya Sputnikovaya Sistema (GLONASS), European Global Navigation Satellite System (Galileo), BeiDou Navigation Satellite System (Beidou-2, BeiDou-3) and Quasi-Zenith Satellite System (QZSS) satellites within a one-year period of 2021. In addition, clock biases that do not exist in orbit files have also been calculated for each system. The results show that average number of GPS and GLONASS satellites are consistent among the products, however, the average GALILEO and BeiDou satellites are significantly changing among the products. The minimum average number of Galileo satellites was calculated for the final, rapid and ultra-rapid orbit products for the Centre national d'études spatiales (CNES (final)), German Research Centre for Geosciences (GFZ (rapid)) and GFZ (ultra) analysis centers, respectively. The minimum average number of satellites for BeiDou-3 medium earth orbit (MEO) and QZSS was calculated for the CODE analysis center. © 2023, TUBITAK. All rights reserved.
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    Towards Geodetic-Level Accuracy in Low-Cost GNSS: Tectonic Velocity Determination Capabilities of the U-Blox ZED-F9P Over a Year Multi-GNSS PPP-AR Time Series
    (Elsevier Ltd, 2025) Duman, H.; Ogutcu, S.; Alçay, S.; Ozdemir, B.N.; Atiz, O.F.; Bulbul, S.
    The growing availability of low-cost dual-frequency GNSS receivers is enhancing their suitability for various kinds of geodetic applications. Geodetic monitoring of the continuous crustal deformation using GNSS time series analysis is one of the commonly used geodetic applications. To maintain the most accurate estimated parameters such as secular velocity, seasonal signal parameters and offsets, geodetic-grade GNSS receivers are commonly used in the GNSS time series analysis. However, due to the increasing availability of low-cost dual-frequency GNSS receivers and advancements in software and hardware, these receivers have now reached a level that supports the GNSS time series analysis. In this study, over a year of multi-GNSS PPP-AR time series of the u-blox ZED-F9P low-cost GNSS receiver are investigated by evaluating the accuracy of the estimated parameters, comparing them with data from a geodetic-grade GNSS receiver monumented on a building roof. The results show that the minimum detrended standard deviation obtained from White Noise (WN) estimation is achieved using GPS + GLONASS + Galileo PPP for both receivers. The computed annual velocity and amplitude differences obtained from the GNSS time series between the u-blox ZED-F9P and the geodetic-grade GNSS receivers using GPS + GLONASS + Galileo PPP-AR are found as 0.6 mm / 0.4 mm / 0.8 mm and 1.5 mm / 0.4 mm / 0.2 mm for north, east, and up components, respectively. © 2025 Elsevier B.V., All rights reserved.