Gerd Gendt

Validation of GPS slant delays using water vapour radiometers and weather models

Slant delay data obtained from global positioning system (GPS) observations carry valuable meteorological information. The spatial distribution of the water vapour can be reconstructed from such slant delays. To estimate the quality of the GPS slant delays two validation studies were carried out. One study was based on the observations of a water vapour radiometer, a second on the analysis fields of a numerical weather model which were used to compute the corresponding GPS delays. Both studies yielded a high correlation between the available slant delays at higher elevation angles but showed deficiencies at low elevations. The mean bias between the GPS zenith delays and the radiometer data is 1.18 mm with a RMS of 6.0 mm. The corresponding bias and RMS of the GPS vs. model comparison are 3.3 mm and 2.9 mm.

GFZ Global Multi-GNSS Network and Data Processing Results

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.

IGS Near Real-Time Products and Their Applications

The primary IGS products, including precise GPS orbits, Earth orientation parameters, and estimated and predicted GPS satellite clocks, are no longer used exclusively for essential geodetic support of scientic research. They are increasingly being used by a wide range of non-academic applications. In these applications, timeliness is extremely critical. To address the timeliness issue, the strengths and weaknesses of current IGS production processes are discussed, new ways to improve the timeliness and quality are explored, and recommendations are proposed to fulfill the application requirements.

A Discussion of IGS Solutions and Their Impact on Geodetic and Geophysical Applications

The International Association of Geodesy officially established the International GPS Service (IGS) on Janaury 1, 1994. Its prime objective is to provide support and a rerefence system for a wide variety of scientific and practical applications involving GPS. To fulfill its role the IGS also generates, in addition to its fundamental products (orbital/staion positions and consistent Earth orientation parameters), additional reference-system products providing the necessary infrastructure, standards, and means of calibrations for timing and various atmospheric applications of GPS. The generation and efficient application of IGS products and their impact on a number of positioning and atmospheric applications, including low earth orbit satellites, is reviewed and discussed. @ 1998 John Wiley & Sons, Inc.

GNSS Activities for Natural Disaster Monitoring and Climate Change Detection at GFZ – An Overview

Natural hazards and climate change are of major concern to the society. Huge losses are reported in recent years. It is widely believed that modern GNSS technologies are effective in hazard monitoring and climate change detection and modelling. Considering the limitations of current accuracy and reliability, sophisticated strategies and models have to be developed. We introduce and overview recent GNSS activities at GFZ in this field, including ground and satellite based atmospheric sounding, reflectometry and GNSS seismology. In addition we summarize recent hardware developments, where new robust on-site hardware systems combining GNSS receiver and other sensors (e.g. seismic sensors and weather sensors) are developed. The main focus of our contribution is recent results of GNSS analysis software developments for real-time applications, where multi-technique (e.g. SLR and GNSS) and multi-system (e.g. GPS and GLONASS) data source can be handled uniquely. The software can run in real-time as well as post-processing modes, and precision of several mm for ground surface deformation can be achieved. We overview the ground and spaced based GNSS atmosphere researches based on the estimation and assimilation of atmosphere parameters, which are among those parameters estimated from our GNSS software. Related projects, applying these new developments, are also introduced.