Zur Nutzung des russischen Satellitensystems GLONASS für die Positionierung und Navigation

Satellite navigation systems have not only revolutionized navigation, but also geodetic positioning. By means of satellite range measurements, positioning accuracies became available that were previously unknown, especially for long baselines. This has long been documented for applications of GPS, the American Global Positioning System. Besides this, there is the Russian Global Navigation Satellite Sys-tem GLONASS. Comparable to GPS from the technical point of view, it is suffering under the economic decline of the Russian Federation, which prevents it from drawing the attention it deserves. Due to the similarities of GPS and GLONASS, both systems may also be used in combined ap-plications. However, since both systems are not entirely compatible to each other, first a number of inter-operability issues have to be solved. Besides receiver hardware issues, these are mainly the differ-ences in coordinate and time reference frames. For both issues, proposed solutions are provided. For the elimination of differences in coordinate reference frames, possible coordinate transformations are introduced, determined using both a conventional and an innovative approach. Another important topic in the usage of GLONASS for high-precision applications is the fact that GLONASS satellites are distinguished by slightly different carrier frequencies instead of different PRN codes. This results in complications, when applying double difference carrier phase measurements to position determination the way it is often done with GPS. To overcome these difficulties and make use of GLONASS double difference carrier phase measurements for positioning, a new mathematical model for double difference carrier phase observations has been developed. These solutions have been implemented in a GLONASS and combined GPS/GLONASS processing software package.Satelliten-Navigationssysteme haben nicht nur die Navigation, sondern auch die geodätische Positionsbestimmung revolutioniert. Mit Hilfe von Entfernungsmessungen zu Satelliten wurden vorher nicht gekannte Genauigkeiten in der Positionierung verfügbar. Für Anwendungen des amerikanischen GPS Global Positioning System ist dies schon lange dokumentiert. Daneben gibt es das russische Global Navigation Satellite System GLONASS. Vom technischen Standpunkt her vergleichbar zu GPS, leidet es unter dem wirtschaftlichen Niedergang der Russischen Föderation und erhält deswegen nicht die Aufmerksamkeit, die es verdient. Aufgrund der Ähnlichkeiten zwischen GPS und GLONASS können beide System auch gemeinsam in kombinierten Anwendungen genutzt werden. Da beide System jedoch nicht vollständig zueinander kompatibel sind, müssen vorher noch einige Fragen der gemeinsamen Nutzung geklärt werden. Neben Fragen der Empfänger-Hardware sind dies hauptsächlich die Unterschiede in den Koordinaten- und Zeit-Bezugssystemen. Für beide Punkte wurden Lösungen vorgeschlagen. Um die Unterschiede in den Koordinaten-Bezugssystemen auszuräumen, werden mögliche Koordinatentransformationen vorgestellt. Diese wurden sowohl über einen konventionellen als auch mit einem innovativen Ansatz bestimmt. Ein anderer wichtiger Punkt in der Nutzung von GLONASS für hochpräzise Anwendungen ist die Tatsache, daß sich GLONASS-Satelliten durch die leicht unterschiedlichen Trägerfrequenzen ihrer Signale unterscheiden, und nicht durch unterschiedliche PRN-Codes. Dies bringt Komplikationen mit sich bei der Anwendung doppelt-differenzierter Trägerphasenmessungen, wie sie bei GPS häufig verwendet werden. Um diese Schwierigkeiten zu überwinden und auch doppelt differenzierte GLONASS-Trägerphasenmessungen für die Positionsbestimmung verwenden zu können, wurde ein neues mathematisches Modell der Doppeldifferenz-Phasenbeobachtungen hergeleitet. Die gewonnenen Erkenntnisse wurden in einem Software-Paket zur Prozessierung von GLONASS und kombinierten GPS/GLONASS Beobachtungen implementiert

Robust Positioning in the Presence of Multipath and NLOS GNSS Signals

GNSS signals can be blocked and reflected by nearby objects, such as buildings, walls, and vehicles. They can also be reflected by the ground and by water. These effects are the dominant source of GNSS positioning errors in dense urban environments, though they can have an impact almost anywhere. Non- line-of-sight (NLOS) reception occurs when the direct path from the transmitter to the receiver is blocked and signals are received only via a reflected path. Multipath interference occurs, as the name suggests, when a signal is received via multiple paths. This can be via the direct path and one or more reflected paths, or it can be via multiple reflected paths. As their error characteristics are different, NLOS and multipath interference typically require different mitigation techniques, though some techniques are applicable to both. Antenna design and advanced receiver signal processing techniques can substantially reduce multipath errors. Unless an antenna array is used, NLOS reception has to be detected using the receiver's ranging and carrier-power-to-noise-density ratio (C/N0) measurements and mitigated within the positioning algorithm. Some NLOS mitigation techniques can also be used to combat severe multipath interference. Multipath interference, but not NLOS reception, can also be mitigated by comparing or combining code and carrier measurements, comparing ranging and C/N0 measurements from signals on different frequencies, and analyzing the time evolution of the ranging and C/N0 measurements

Advanced tracking systems design and analysis

The results of an assessment of several types of high-accuracy tracking systems proposed to track the spacecraft in the National Aeronautics and Space Administration (NASA) Advanced Tracking and Data Relay Satellite System (ATDRSS) are summarized. Tracking systems based on the use of interferometry and ranging are investigated. For each system, the top-level system design and operations concept are provided. A comparative system assessment is presented in terms of orbit determination performance, ATDRSS impacts, life-cycle cost, and technological risk

Integer Ambiguity Resolution for Multi-GNSS and Multi-Signal Raw Phase Observations

The continuous modernisation of existing Global Navigation Satellite Systems (GNSS) and the development of new systems with a multitude of different carrier frequencies and a variety of signal modulations creates a true multi-GNSS and multi-signal environment available today. Still most precise GNSS processing strategies rely on dual-frequency measurements only by applying the Ionosphere-Free (IF) Linear Combination (LC) of GNSS observables and therefore do not benefit from the available multi-signal environment. While in this processing approach the first order effect of the ionospheric delay can be eliminated almost completely, the formation of linear combinations of GNSS observables leads to a noise increase for the resulting observations and a loss of some of the physical characteristics of the original signals, like the integer nature of the carrier phase ambiguity. In order to benefit from the multi-GNSS and multi-signal environment available today, the scientific analyses and precise applications presented in this work are based on the raw observation processing approach, which makes use of the original (raw) observations without forming any linear combinations or differences of GNSS observables. This processing strategy provides the flexibility to make use of all or a selection of available multi-GNSS and multi-signal raw observations, which are jointly processed in a single adjustment as there is no inherent limitation on the number of usable signals. The renunciation of linear combinations and observation differences preserves the physical characteristics of individual signals and implies that multi-signal biases and ionospheric delays need to be properly determined or corrected in the parameter estimation process. The raw observation processing approach is used in this work to jointly process measurements from up to three different GNSS, including eleven signals tracked on up to eight different carrier frequencies in one single adjustment. The bias handling for multi-GNSS and multi-signal applications is analysed with a focus on physically meaningful parameter estimates to demonstrate the benefits of handling clock offset parameters, multi-signal code biases and ionospheric delay estimates in a physically meaningful and consistent way. In this context, receiver-specific multi-GNSS and multisignal biases are analysed and calibrated by the use of a GNSS signal simulator. The disadvantages of eliminating physical characteristics due to the formation of linear combinations of observations or commonly used parameter estimation strategies are demonstrated and discussed. The carrier phase Integer Ambiguity Resolution (IAR) approach developed and implemented in the course of this work is based on the joint processing of multi-GNSS and multi-signal raw observations without forming any linear combinations or observation differences. Details of the implemented IAR approach are described and the performance is analysed for available carrier signal frequencies of different GNSS. Achieved results are compared to the conventional IAR approach based on IF linear combinations and the so called Widelane (WL) and Narrowlane (NL) ambiguities. In addition, the resolution of inter-system integer ambiguities is analysed for common GNSS signal frequencies. The performance of the implemented IAR approach is demonstrated and analysed by the joint Precise Orbit Determination (POD) of multi-GNSS satellites based on fixed multi-frequency carrier phase ambiguities. The improvement of the satellite orbit and clock quality by fixing raw observation ambiguities confirms the successful implementation of the IAR approach based on raw observation processing. Multi-GNSS satellite orbits and clock offsets determined with this approach are compared to results generated with the conventional IF linear combination processing approach and independent external products. This comparison demonstrates an at least equivalent performance of the implemented IAR approach based on raw observation processing. In addition, the fixed raw observation ambiguities are used to investigate and discuss characteristics of multi-GNSS and multi-frequency phase biases

Mariner Mars 1971 optical navigation demonstration

The feasibility of using a combination of spacecraft-based optical data and earth-based Doppler data to perform near-real-time approach navigation was demonstrated by the Mariner Mars 71 Project. The important findings, conclusions, and recommendations are documented. A summary along with publications and papers giving additional details on the objectives of the demonstration are provided. Instrument calibration and performance as well as navigation and science results are reported

Altimetric system: Earth observing system. Volume 2h: Panel report

A rationale and recommendations for planning, implementing, and operating an altimetric system aboard the Earth observing system (Eos) spacecraft is provided. In keeping with the recommendations of the Eos Science and Mission Requirements Working Group, a complete altimetric system is defined that is capable of perpetuating the data set to be derived from TOPEX/Poseidon, enabling key scientific questions to be addressed. Since the scientific utility and technical maturity of spaceborne radar altimeters is well documented, the discussion is limited to highlighting those Eos-specific considerations that materially impact upon radar altimetric measurements

Satellitenorbit und -ephemeridenbestimmung mit Hilfe von Intersatellitenverbindungen

Global navigation satellite systems like GPS, GLONASS or the future systems like Galileo require precise orbit and clock estimates in order to provide high positioning performance. Within the frame of this Ph. D. thesis, the theory of orbit determination and orbit computation is reviewed and a new approach for precise orbit and ephemeris determination using inter-satellite links is developed. To investigate the achievable accuracy, models of the various perturbing forces acting on a satellite have been elaborated and coded in a complex software package, allowing system level performance analysis as well as detailed evaluation of orbit prediction and orbit estimation algorithms. Several satellite constellations have been simulated, involving nearly all classes of orbit altitude and the results are compared. The purpose of orbit determination in a satellite navigation system is the derivation of ephemeris parameters which can be broadcast to the user community (or the other satellites) and allow easy computation of the satellites position at the desired epoch. The broadcast ephemeris model of both today existing satellite navigation systems, GPS and GLONASS are investigated, as well as two new models developed within this thesis, which are derivates of the GLONASS model. Furthermore, the topic of autonomous onboard processing is addressed. A conceptual design for an onboard orbit estimator is proposed and investigated with respect to the computational load. The algorithms have been implemented. The main benefits of ISL onboard processing, especially with respect to the great potential to ephemeris and clock state monitoring are investigated using complex simulations of failure scenarios. By simulating several types of non-integrity cases, it is showed that one single fault detection mechanism is likely to be insufficient. Within the algorithm design of the onboard processor, a reasonable combination of fault detection mechanisms is presented, covering different fault cases.Globale Navigationssysteme wie GPS, GLONASS oder zukünftige Systeme wie Galileo erfordern die hochpräzise Bestimmung der Orbital- und Uhrenparameter, um hohe Navigationsgenauigkeit bieten zu können. Im Rahmen dieser Dissertation wurde die Theorie der Orbitprädiktion und der Orbitbestimmung erörtert und ein neuer Ansatz für die präzisen Orbitbestimmung mit Hilfe von Intersatelliten-Messungen entwickelt. Um die erreichbare Genauigkeit und Präzision der Orbitbestimmung zu untersuchen, wurden mathematische Modelle der zahlreiche Orbitstörungen erarbeitet und in einem komplexen Software-Paket implemetiert. Dieses bietet die Möglichkeit für Systemstudien von Satellitennavigations-Systemen beliebiger Orbitklassen, sowie zur detaillierten Untersuchung spezieller Fragestellungen der Orbitprädiktion und -bestimmung. Eine Reihe von Simulationen mit existierenden sowie fiktiven Satelliten-Navigations-Systemen wurden durchgeführt, deren Ergebnisse in dieser Arbeit präsentiert werden. Die präzise Orbitbestimmung in einem SatNav-System ist kein Selbstzweck, sondern dient lediglich der Bestimmung der Ephemeridenparameter, die - vom Satellite gesendet - es dem Nutzer-Empfänger erlauben, mit Hilfe einfacher Berechnungen die Position des Satelliten zu ermitteln. Die Ephemeridenformate beider existierender SatNav-Systeme - GPS und GLONASS - wurden untersucht und mit zwei weiteren Formaten verglichen, die im Rahmen dieser Arbeit entwickelt wurden. Desweiteren wurde das Thema der bordautonomen Verarbeitung von Messungen behandelt. Ein konzeptuelles Design für einen Onboard-Prozessor wurde vorgeschlagen und die Algorithmen implementiert. Dabei erfolgte eine Abschätzung der benötigten Prozessorleistung. Einer der Hauptvorteile der bordautonomen Verarbeitung von Intersatellitenmessungen, die Möglichkeit zur Überwachung der Integrität der Ephemeriden und Uhrenparameter, wurde in komplexen Simulationen untersucht. Durch die Simulation verschiedener Fehlerfälle wurde gezeigt, das kein Detektionsmechanismus allein, wohl aber eine sinnvolle Kombination solcher Mechanismen, zur bordautonomen Integritätsüberwachung geeignet sind. Die Ergebissen werden hier präsentiert

Optical guidance vidicon test program

A laboratory and field test program was conducted to quantify the optical navigation parameters of the Mariner vidicons. A scene simulator and a camera were designed and built for vidicon tests under a wide variety of conditions. Laboratory tests characterized error sources important to the optical navigation process and field tests verified star sensitivity and characterized comet optical guidance parameters. The equipment, tests and data reduction techniques used are described. Key test results are listed. A substantial increase in the understanding of the use of selenium vidicons as detectors for spacecraft optical guidance was achieved, indicating a reduction in residual offset errors by a factor of two to four to the single pixel level