How to Deal With Station Dependent Errors - New Developments of the Absolute Field Calibration of PCV and Phase-Multipath With a Precise Robot 1

BIOGRAPHY Dr. Günter Seeber has been Professor at the Institut für Erdmessung, Universität Hannover since 1973, where he teaches satellite geodesy, geodetic astronomy and marine geodesy. He has specialized in satellite positioning techniques since 1969 and has published several scientific papers and books in the field of satellite and marine geodesy. Volker Böder and Falko Menge received their Dipl.-Ing. in Geodesy from the Universität Hannover and are currently employed as research associates in satellite positioning at the Institut für Erdmessung. Their current project concerns the GPS antenna and multipath calibration. Dr. Gerhard Wübbena received his degrees in Geodesy from the Universität Hannover. He has worked in the field of GPS since 1983 and developed the program system GEONAP. In 1990 he founded the company Geo++ , which develops satellite navigation and positioning software and systems. Dr. Martin Schmitz also received his degrees in Geodesy from the Universität Hannover. Present projects are i.e. active reference networks for highly precise RTK phase positioning (GNSMART) and the GPS station calibration project. ABSTRACT It has already been shown, that the absolute field calibration of GPS antenna phase center variations (PCV) with a precisely calibrated robot yields results with high accuracy and repeatability. Precise station independent absolute PCV are obtained. Many examples for different antenna types underline the high resolution in elevation and azimuth. It can be expected, that also IGS will switch to absolute PCV in a foreseeable period of time. The precision of the PCV enables a separation from the multipath (MP) errors. For active reference station networks, also providing real-time corrections, carrier phase multipath is an urgent field of research, since its periodic character also influences the correct instantaneous ambiguity resolution and the real time kinematic (RTK) positioning. Different scenarios from reduction to estimation are conceivable how to deal with this error term using a robot. The most recent developments of this approach and options for further research will be presented

Accuracy analysis of vertical deflection data observed with the Hannover Digital Zenith Camera System TZK2-D

This paper analyses the accuracy of vertical deflection measurements carried out with the Digital Zenith Camera System TZK2-D, an astrogeodetic state-of-the-art instrumentation developed at the University of Hannover. During 107 nights over a period of 3.5 years, the system was used for repeated vertical deflection observations at a selected station in Hannover. The acquired data set consists of about 27,300 single measurements and covers 276 h of observation time, respectively. For the data collected at an earlier stage of development (2003 to 2004), the accuracy of the nightly mean values has been found to be about 0".10-0".12. Due to applying a refined observation strategy since 2005, the accuracy of the vertical deflection measurements was enhanced into the unprecedented range of 0".05-0".08. Accessing the accuracy level of 0".05 requires usually 1 h of observational data, while the 0".08 accuracy level is attained after 20 min measurement time. In comparison to the analogue era of geodetic astronomy, the accuracy of vertical deflection observations is significantly improved by about one order of magnitude

Möglichkeitsdenken. Utopie und Dystopie in der Gegenwart

Utopien denken Möglichkeiten von Zukunft. Mit Beginn der historischen Moderne, in der die Erwartung an die Zukunft die Erfahrung der Vergangenheit übersteigt, entstehen in der je aktuellen Gegenwart Entwürfe, die Utopien genannt werden können. Die Temporalisierung der Erfahrung macht Projektionen in die Zukunft möglich (Reinhart Koselleck). Diese sind nie eindeutig. Sie liefern mehrdeutige Wunsch- und Schreckbilder auch in eigentümlichen Verschränkungen. Die Einsicht in diese Dialektik nimmt mit dem Grad der Selbstreferentialität von Zukunftsentwürfen zu; Utopie und Dystopie bedingen sich wechselseitig. – Gegenwärtig leben wir mit außerordentlich unsicheren Zukunftsperspektiven. Haben Utopien nur in Dystopien überlebt? Nach dem Ende des Utopismus-Verdachts am Beginn der 90er Jahre geht es heute um eine Bestandsaufnahme von Zukunftspotentialen, um Diskussionen von Denkformen des Hypothetisch-Möglichen. Bietet die Tradition des utopischen Denkens Anknüpfungspunkte für aktuelle, positiv oder negativ konnotierte Zukunftsbeschreibungen? Wunsch- oder Warnbilder sind noch immer jenem utopischen Impuls verpflichtet, der den Blick aus der Gegenwart in die Zukunft richten will. Die Frage nach der Zukunft utopischen Denkens stellt somit in den Möglichkeiten temporalen, visionären und konjunktivischen Denkens zugleich die Frage nach dem Ort des Gesellschaftlichen und der Gesellschaft heute – und damit die Frage nach der Verbindlichkeit von Tradition, und das heißt auch: nach Traditionen des Utopischen

Mutual Validation of GNSS Height Measurements and High-precision Geometric-astronomical Leveling

The method of geometric-astronomical leveling is presented as a suited technique for the validation of GNSS (Global Navigation Satellite System) heights. In geometric-astronomical leveling, the ellipsoidal height differences are obtained by combining conventional spirit leveling and astronomical leveling. Astronomical leveling with recently developed digital zenith camera systems is capable of providing the geometry of equipotential surfaces of the gravity field accurate to a few 0.1 mm per km. This is comparable to the accuracy of spirit leveling. Consequently, geometric-astronomical leveling yields accurate ellipsoidal height differences that may serve as an independent check on GNSS height measurements at local scales. A test was performed in a local geodetic network near Hanover. GPS observations were simultaneously carried out at five stations over a time span of 48 h and processed considering state-of-the-art techniques and sophisticated new approaches to reduce station-dependent errors. The comparison of GPS height differences with those from geometric-astronomical leveling shows a promising agreement of some millimeters. The experiment indicates the currently achievable accuracy level of GPS height measurements and demonstrates the practical applicability of the proposed approach for the validation of GNSS height measurements as well as the evaluation of GNSS height processing strategies