Browsing by Author "Duman, Huseyin"

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Citation - WoS: 4
Citation - Scopus: 4
Analysis of Ionospheric Vtec Retrieved From Multi-Instrument Observations
(MDPI, 2024) Öztan, Gürkan; Duman, Huseyin; Alçay, Salih; Öğütçu, Sermet; Özdemir, Behlül Numan
This study examines the Vertical Total Electron Content (VTEC) estimation performance of multi-instruments on a global scale during different ionospheric conditions. For this purpose, GNSS-based VTEC data from Global Ionosphere Maps (GIMs), COSMIC (F7/C2)-Feng-Yun 3C (FY3C) radio occultation (RO) VTEC, SWARM-VTEC, and JASON-VTEC were utilized. VTEC assessments were conducted on three distinct days: geomagnetic active (17 March 2015), solar active (22 December 2021), and quiet (11 December 2021). The VTEC values of COSMIC/FY3C RO, SWARM, and JASON were compared with data retrieved from GIMs. According to the results, COSMIC RO-VTEC is more consistent with GIM-VTEC on a quiet day (the mean of the differences is 4.38 TECU), while the mean of FY3C RO-GIM differences is 7.33 TECU on a geomagnetic active day. The range of VTEC differences between JASON and GIM is relatively smaller on a quiet day, and the mean of differences on active/quiet days is less than 6 TECU. Besides the daily comparison, long-term results (1 January-31 December 2015) were also analyzed by considering active and quiet periods. Results show that Root Mean Square Error (RMSE) values of COSMIC RO, FY3C RO, SWARM, and JASON are 5.02 TECU, 6.81 TECU, 16.25 TECU, and 5.53 TECU for the quiet period, and 5.21 TECU, 7.07 TECU, 17.48 TECU, and 5.90 TECU for the active period, respectively. The accuracy of each data source was affected by solar/geomagnetic activities. The deviation of SWARM-VTEC is relatively greater. The main reason for the significant differences in SWARM-GIM results is the atmospheric measurement range of SWARM satellites (460 km-20,200 km (SWARM A, C) and 520 km-20,200 km (SWARM B), which do not contain a significant part of the ionosphere in terms of VTEC estimation.
Citation - WoS: 2
Citation - Scopus: 3
The Effect of Ambiguity Resolution on the Precision of the Gps/Galileo Ppp Using a U-Blox Zed-F9p Low-Cost Gnss Receiver
(Elsevier Sci Ltd, 2025) Ogutcu, Sermet; Duman, Huseyin; Ozdemir, Behlul Numan; Alcay, Salih
Thanks to the increasing number of low-cost dual-frequency GNSS receivers available on the market, the usability of these receivers for geodetic applications is increasing. Recently, PRIDE Lab at GNSS Research Center of Wuhan University has started to produce GNSS observable-specific phase biases for all-frequency. This enables precise point positioning with ambiguity resolution (PPP-AR) not only for conventional frequencies but also for other arbitrary frequencies. In this work, static and kinematic PPP-AR precision of the u-blox ZED-F9P low-cost GNSS receiver are investigated by comparing it with a geodetic-grade GNSS receiver using GPSonly, Galileo-only, and GPS + Galileo combinations for nearly two months period. Wide-lane (WL) and Narrow-lane (NL) AR fixing rates, cycle slips, code multipath, and frequency availability are also investigated for both receivers. In the positioning domain, GPSonly, Galileo-only, and GPS + Galileo PPP positioning precision using float ambiguities is significantly improved after AR for both receivers. GPS + Galileo PPP provides the best precision comparing with the other PPP solutions for both receivers using float and fix ambiguities. For static GPS + Galileo PPP-AR, the standard deviation of north, east, and up components are computed as 2.7/1.7/3.2 mm and 2.2/2.3/5.4 mm for the geodetic receiver and the u-blox receiver, respectively. The results also reveal that kinematic PPP-AR for the u-blox receiver is not as reliable as the geodetic-grade receiver yet suggesting potential for improvement in future iterations. (c) 2024 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.