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Author

Maik Uhlemann

Bio: Maik Uhlemann is an academic researcher. The author has contributed to research in topics: GNSS applications & Satellite. The author has an hindex of 5, co-authored 6 publications receiving 264 citations.

Papers
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Journal ArticleDOI
TL;DR: This article analyzes the orbit and clock quality of the Galileo products of four MGEX analysis centers for a common time period of 20 weeks and finds that orbit comparisons of the individual analysis centers have a consistency at the 5–30 cm level.

129 citations

Book ChapterDOI
01 Jan 2015
TL;DR: The Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences (GFZ) has been operating a worldwide Global Navigation Satellite Systems (GNSS) station network since many years.
Abstract: The Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences (GFZ) is operating a worldwide Global Navigation Satellite Systems (GNSS) station network since many years. With recent developments in receiver technology and new upcoming navigation satellite systems like Galileo an upgrade of our stations was needed to track all GNSS. We will present the current status and setup of our station network and the plan for future upgrades. All modernized stations are presently contributing to the Multi-GNSS EXperiment (MGEX) of the International GNSS Service (IGS) as well as to the COoperative Network of GNSS Observations (CONGO). Selected results from a combined GPS/Galileo data processing will be shown. The used data were taken mainly from the public available MGEX network whereas the focus of analysis lies on precise orbit and clock determination of Galileo In-Orbit-Validation (IOV) satellites. Quality assessments are given which are based on orbit overlap statistics, clock stabilities as well as comparisons with external solutions. Additionally an independent validation of the orbits is derived through Satellite Laser Ranging (SLR) measurements. Furthermore some initial results of BeiDou data processing are shown which were derived with an experimental set of MGEX data.

86 citations

Journal ArticleDOI
TL;DR: In this article, satellite antenna phase center offsets for the Galileo In-Orbit Validation (IOV) and Full Operational Capability (FOC) satellites are estimated by two different analysis centers based on tracking data of a global GNSS network.
Abstract: Satellite antenna phase center offsets for the Galileo In-Orbit Validation (IOV) and Full Operational Capability (FOC) satellites are estimated by two different analysis centers based on tracking data of a global GNSS network. The mean x- and y-offsets could be determined with a precision of a few centimeters. However, daily estimates of the x-offsets of the IOV satellites show pronounced systematic effects with a peak-to-peak amplitude of up to 70 cm that depend on the orbit model and the elevation of the Sun above the orbital plane. For the IOV y-offsets, no dependence on the orbit model exists but the scatter strongly depends on the elevation of the Sun above the orbital plane. In general, these systematic effects are significantly smaller for the FOC satellites. The z-offsets of the two analysis centers agree within the 10–15 cm level, and the time series do not show systematic effects. The application of an averaged Galileo satellite antenna model obtained from the two solutions results in a reduction of orbit day boundary discontinuities by up to one third—even if an independent software package is used.

44 citations

Journal ArticleDOI
TL;DR: In this paper, the quality of the Galileo orbit determination based on Global Navigation Satellite System (GNSS) and Satellite Laser Ranging (SLR) observations is assessed based on two test periods, and the estimated satellite clock parameters are used as quality indicator for the orbits.
Abstract: The first two Galileo In-Orbit Validation satellites were launched in October 2011 and started continuous signal transmission on all frequencies in early 2012. Both satellites are equipped with two different types of clocks, namely rubidium clocks and hydrogen masers. Based on two test periods, the quality of the Galileo orbit determination based on Global Navigation Satellite System (GNSS) and Satellite Laser Ranging (SLR) observations is assessed. The estimated satellite clock parameters are used as quality indicator for the orbits: A bump at orbital periods in the Allan deviation indicates systematic errors in the GNSS-only orbit determination. These errors almost vanish if SLR observations are considered in addition. As the internal consistency is degraded by the combination, the offset of the SLR reflector is shifted by +5 cm, resulting in an improved orbit consistency as well as accuracy. Another approach to reduce the systematic errors of the GNSS-only orbit determination employs constraints for the clock estimates with respect to a linear model. In general, one decimeter orbit accuracy could be achieved.

43 citations

01 Jan 2012
TL;DR: One of the main goal of this study is the precise orbit & clock determination of GALILEO’s Giove and IOV satellites and also the investigation of station tracking behavior and orbit issues.
Abstract: One of the main goal of this study is the precise orbit & clock determination of GALILEO’s Giove (E01/E16) and IOV (E11/E12) satellites and also the investigation of station tracking behavior and orbit issues. The advantage of the modern ‘COoperative Network for GIOVE Observation’ (CONGO) tracking network can be found in homogeneous observation types and station hardware (almost all with JAVAD receivers, but different antenna types).

8 citations


Cited by
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Journal ArticleDOI
TL;DR: The status and tracking capabilities of the IGS monitoring station network are presented and the multi-GNSS products derived from this resource are discussed and the achieved performance is assessed and related to the current level of space segment and user equipment characterization.

645 citations

Book ChapterDOI
01 Jan 2017
TL;DR: The International global navigation satellite system (GNSS) Service (IGS) is an organization devoted to the generation of high-precision GNSS data and products; a service that benefits science and society.
Abstract: The International global navigation satellite system (GNSS ) Service (IGS ) is an organization devoted to the generation of high-precision GNSS data and products; a service that benefits science and society. It is a voluntary federation of over 200 self-funding agencies, universities, and research institutions in more than 100 countries. Established in 1992 and formally launched on 1st January 1994, the IGS has delivered an uninterrupted time series of products that are utilized by a broad spectrum of users. IGS products have evolved over time, including the provision of GNSS data for constellations other than GPS , and the addition of real-time GNSS data and products.

299 citations

Journal ArticleDOI
TL;DR: This paper develops a four-system positioning model to make full use of all available observations from different GNSSs to bring about significant improvement of satellite visibility, spatial geometry, dilution of precision, convergence, accuracy, continuity and reliability.
Abstract: The world of satellite navigation is undergoing dramatic changes with the rapid development of multi-constellation Global Navigation Satellite Systems (GNSSs). At the moment more than 70 satellites are already in view, and about 120 satellites will be available once all four systems (BeiDou + Galileo + GLONASS + GPS) are fully deployed in the next few years. This will bring great opportunities and challenges for both scientific and engineering applications. In this paper we develop a four-system positioning model to make full use of all available observations from different GNSSs. The significant improvement of satellite visibility, spatial geometry, dilution of precision, convergence, accuracy, continuity and reliability that a combining utilization of multi-GNSS brings to precise positioning are carefully analyzed and evaluated, especially in constrained environments.

296 citations

Journal ArticleDOI
TL;DR: A consistent analysis of signal-in-space ranging errors (SISREs) is presented for all current satellite navigation systems, considering both global average values and worst-user-location statistics, based on 1 year of broadcast ephemeris messages of the Global Positioning System, GLONASS, Galileo, BeiDou and QZSS collected with a near-global receiver network.
Abstract: A consistent analysis of signal-in-space ranging errors (SISREs) is presented for all current satellite navigation systems, considering both global average values and worst-user-location statistics. The analysis is based on 1 year of broadcast ephemeris messages of the Global Positioning System (GPS), GLONASS, Galileo, BeiDou and QZSS collected with a near-global receiver network. Position and clock values derived from the navigation data are compared against precise orbit and clock products provided by the International GNSS Service and its multi-GNSS experiment. Satellite laser ranging measurements are used for a complementary and independent assessment of the orbit-only SISRE contribution. The need for proper consideration of antenna offsets is highlighted and block-/constellation-specific radial antenna offset values for the center-of-mass correction of broadcast orbits are derived. Likewise, the need for application of differential code biases in the comparison of broadcast and precise clock products is emphasized. For GPS, the analysis of the legacy navigation message is complemented by a discussion of the CNAV message performance based on the first CNAV test campaign in June 2013. Global average SISRE values for the individual constellations amount to 0.7 ± 0.02 m (GPS), 1.5 ± 0.1 m (BeiDou), 1.6 ± 0.3 m (Galileo), 1.9 ± 0.1 m (GLONASS), and 0.6 ± 0.2 m (QZSS) over a 12-month period in 2013/2014.

245 citations

01 Jan 2013
TL;DR: The Experiment (MGEX) as mentioned in this paper is an early-familiarization system for GNSS systems to enable their incorporation into high-precision GNSS modeling and analysis, and it is based on the MGEX project.
Abstract: With a total of four new and emerging constellations (BeiDou, Galileo, QZSS, IRN SS) as well as the ongoing modernization of GPS and GLONASS the world of satellite navigation presently experiences dramatic changes. Facing these challenges, the International GNSS Service (IGS) has initiated the Multi-GNSS Experiment (MGEX) to enable an early familiarization with the new systems and to prepare their incorporation into high-precision GNSS modeling and analysis. The paper reports on the status of the new constellations and the MGEX project as of September 2013. The offline and real-time segment of the multi-GNSS network built up so far are described and initial data products are presented. Recent results for individual systems are highlighted and necessary steps towards a comprehensive multi-GNSS service are identified.

226 citations