Browsing by Subject "GPS"

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Application of Global Positioning System slant path delay data for mesoscale modelverification and four-dimensional variational assimilation
(2010) Zus, Florian; Wulfmeyer, Volker
Observation modeling is required in order to make use of slant path delay data, processed from ground-based Global Positioning System (GPS) measurements, for verification purposes and numerical weather prediction. A rigorous ray-tracing algorithm based on the Euler-Lagrange equation derived from Fermat's principle is developed to simulate the propagation of GPS radio signals in a mesoscale model. The ray-tracing algorithm is based on a finite difference scheme and allows the direct numerical simulation of GPS slant path delays.
Model evaluation and data assimilation impact studies in the framework of COPS
(2012) Schwitalla, Thomas; Wulfmeyer, Volker
The goal of this thesis was the study of new approaches for improving and investigating quantitative precipitation forecasting (QPF), e.g., by optimizing model resolution, physics combination, and data assimilation. A forecasting system based on the Mesoscale Model 5 (MM5) was compared against other operational numerical weather prediction models from Meteo France, MeteoSwiss and the German Weather Service primarily with respect to daytime precipitation. First, a notable daytime dry bias was observed. It appears to be the result of a too small high-resolution domain and the switched-off convection parameterization from the second to the innermost domain. Even the application of a 4-dimensional variational data assimilation (4DVAR) with GPS slant total delays (STD) does not solve this problem due to inconsistent model physics between the 4DVAR and the forecasting model. Nevertheless, the MM5 is in good agreement with the shape of the observed diurnal cycle after the spin-up phase. As the development of the MM5 was suspended, a transition to the new Weather Research and Forecasting (WRF) model system was made after the D-PHASE period (end of 2007). This system features state-of-the-art physics packages and also a variational data assimilation system. As a new observing system, GPS Zenith Total Delay (ZTD) data from Central Europe were incorporated into the 3-dimensional variational data assimilation (3DVAR) system to further improve the initial water vapor field. A first study with this system revealed an improvement of the integrated water vapor RMSE of about 15% and a small but positive impact on the spatial and quantitative precipitation forecast. Additionally, the importance of assimilating upper air observations and the necessity to select a large, convection permitting model domain emerged. Finally a rapid update cycle (RUC) approach, comparable to operational forecast centers, has been developed for a convection-permitting configuration of the WRF model. The system is capable to assimilate radar observations from Germany and France, GPS-ZTD data and satellite radiances and can be applied even for near real-time applications. First experiments with this system show promising results in comparison to other operational models.
Untersuchungen zur Ertragskartierung während der Getreideernte mit dem Mähdrescher
(1997) Reitz, Peter
Die Getreideernte in den Industrieländern wird heute ausschließlich mit dem Mähdrescher durchgeführt. Durch eine gleichzeitige Ertragskartierung werden die Voraussetzungen für eine teilflächenspezifische Feldbewirtschaftung geschaffen. Aus den geokartierten Ertragsdaten lassen sich Rückschlüsse über kleinräumige Unterscheide in den Wachstumsbedingungen innerhalb eines Feldes ziehen. In der vorliegenden Arbeit werden die theoretischen Grundlagen zur Ertragskartierung und ein Verfahren zum Betrieb des Mähdreschers mit geokodierten Teilflächendaten entwickelt und untersucht. Zu deren Realisierung werden Module für die Erfassung, Übertragung, Verarbeitung und Umsetzung geokodierter Teilflächendaten benötigt.