Andreas Knöpfler

Accurate Estimation of Atmospheric Water Vapor Using GNSS Observations and Surface Meteorological Data

Remote sensing data have been increasingly used to measure the content of water vapor in the atmosphere and to characterize its temporal and spatial variations. In this paper, we use observations from Global Navigation Satellite System(s) (GNSS) to estimate time series of precipitable water vapor (PWV) by applying the technique of precise point positioning. For an accurate quantification of the absolute PWV, it is necessary to combine the GNSS observations with meteorological data measured directly or inferred at the GNSS site. In addition, measurements of the surface temperature are used to calculate the empirical constant required to convert the GNSS-based delay into water vapor. Our results show strong agreement between the total precipitable water estimated based on GNSS observations and that measured by the sensor MEdium Resolution Imaging Spectrometer with a mean RMS value of 0.98 mm. In a similar way, we compared the GNSS-based total PWV estimates with those produced by the Weather Research and Forecasting (WRF) Modeling System. We found that the WRF model simulations agree well with the GNSS estimates with a mean RMS value of 0.97 mm.

First Results of Relative Field Calibration of a GPS Antenna at BCAL/UFPR (Baseline Calibration Station for GNSS Antennas at UFPR/Brazil)

The precise and accurate determination as well as the usage of individual calibration values of GNSS (Global Navigation Satellite Systems) antennas are of fundamental importance for state-of-the-art GNSS positioning at millimeter accuracy level, especially concerning the precise determination of the height component. Calibration values can be determined in various ways (relative vs. absolute, chamber vs. field). Within the transnational research project “PROBRAL: Precise positioning and height determination by means of GPS – Modeling of errors and transformation into physical heights”, the first relative antenna calibration field of Latin America was established.

GURN (GNSS Upper Rhine Graben Network): Research Goals and First Results of a Transnational Geo-scientific Network

The Upper Rhine Graben (URG) is a north-northeast trending rift system belonging to the European Cenozoic Rift System. Today, the southern part of the URG is seismically still active. Earthquakes of magnitude five have a recurrence time of approximately a few decades. In order to monitor and to determine recent crustal displacements in the URG area, the transnational cooperation GURN (GNSS Upper Rhine Graben Network) was established in September 2008. Within GURN geo-scientific research is carried out. The focus is on processing and analysing of observation data of continuously operating GNSS (Global Navigation Satellite Systems, e.g. GPS) sites.

Establishing A Gnss Receiver Antenna Calibration Field in the Framework Of Probral

PROBRAL - Precise positioning and height determination by means of GPS: Modeling of errors and transformation into physical heights is the name of a joint venture between the Department of Geomatics (DGEOM), Federal University of Parana (UFPR), Curitiba (Brazil) and the Geodetic Institute (GIK), University Karlsruhe (TH), Karlsruhe (Germany). The aim of this research project, which started in 2006 and is founded by the Brazilian academic exchange service CAPES and the German academic exchange service DAAD, is to validate and to improve the quality of GNSS-based positioning, especially concerning the height component.

BCAL/UFPR: The GNSS Antenna Calibration Service of Latin America

The usage of individual calibration values for GNSS (Global Navigation Satellite Systems) antennas is of fundamental importance for state-of-the-art GNSS positioning at millimeter accuracy level, especially concerning precise height determination. In Brazil, the awareness of the user community regarding this important error source has to be sharpened. In contrast to Europe, where manifold research is carried out focusing on antenna calibration and different agencies provide calibration services, in Latin America the users have to be sensitized with respect to receiver antenna handling. Therefore, the first Latin American GNSS antenna calibration basis BCAL/UFPR (Baseline Calibration Station for GNSS Antennas at UFPR) was established at the Federal University of Parana (UFPR; Curitiba, Parana, Brazil) in close cooperation with the Geodetic Institute of the Karlsruhe Institute of Technology (Karlsruhe, Germany). The BCAL/UFPR is actually equipped with three pillars and enables the determination of antenna parameters applying the relative field calibration approach. The antenna modeling parameters are derived at absolute level, because the reference antenna (3D choke ring antenna type) was calibrated absolutely by Geo++ (Garbsen, Germany). In this context, five antennas of the same model (Trimble Zephyr GNSS Geodetic II) were calibrated at BCAL/UFPR. The goal of the case study is to verify the difference between individual parameters determined at BCAL/UFPR and mean parameters published by the NGS (National Geodetic Service, USA). This article presents information related to BCAL/UFPR and discusses the results of recent calibration investigations.

Integration of InSAR and GNSS Observations for the Determination of Atmospheric Water Vapour

High spatially and temporally variable atmospheric water vapour causes an unknown delay in microwave signals transmitted by space-borne sensors. This delay is considered as a major limitation in Interferometric Synthetic Aperture Radar (InSAR) applications as well as high-precision applications of Global Navigation Satellite Systems (GNSS). On the other hand, the delay could be quantified to derive atmospheric parameters such as water vapour. Temporal variability of water vapour is well estimated from ongoing GNSS measurements, while InSAR provides information about the spatial variations of water vapour. This project aims at assimilating InSAR phase observations and spatially-sparse GNSS measurements for the determination of atmospheric water vapour. In this contribution GNSS-based water vapour calculations and assessment of different strategies are presented. Work in progress is also reported including some preliminary results.

An Inventory of Surface Movements in the Upper Rhine Graben Area, Southwest Germany, from SAR-Interferometry, GNSS and Precise Levelling

Recent surface movements in the Upper Rhine Graben (URG) area are investigated with geodetic techniques. Line of sight (LOS) displacement rates from SAR interferometry (InSAR), horizontal and vertical rates from coordinate time series of permanent GNSS sites and vertical rates from precise levelling measurements are estimated with high accuracy. We show that the data sets are capable of providing detailed insight into the current movements in the URG area, which is required for a better understanding of geodynamic processes as well as for a reasonable exploitation of geopotentials in the URG. This paper focusses on a comparison of results from InSAR and levelling on a regional and on a local scale. A case study highlights temporal differences in the deformation characteristics of an oil extraction area detected from ERS-1/2 and Envisat data as well as from levelling measurements in multiple epochs. In order to benefit from the advantages of each technique, our work aims on a proper combination to consistently link the different observation methods in a rigorous multi-technique approach.