Ray-traced Delays in the Atmosphere - Open Research Data (Radiate ORD)
In the troposphere (strictly speaking in the neutral atmosphere up to about 80 kilometres), signals from Global Navigation Satellite Systems (GNSS) such as the U.S. Global Positioning System (GPS) or the European system Galileo are slower than velocity of light. If not corrected for those tropospheric delays, the range measurements between ground stations and GNSS satellites would be too long by up to 20 metres, thereby significantly degrading the positioning accuracy. Along those lines, errors in the delay models propagate into geodetic parameters such as station coordinates, thus limiting high-accuracy applications like reference frame realisation where we are striving for millimetre-accuracy, but also navigation tasks with GNSS with decimetre or metre-accuracies. Reference frames of highest accuracy are critical for many applications, e.g. for the observation of sea level rise.
Technische Universität Wien (TU Wien) world-renowned for determining and providing the most accurate tropospheric delay models globally available. These models comprise the Vienna Mapping Functions (VMF1), which are determined from operational data of the European Centre for Medium-Range Weather Forecasts (ECMWF) for specific geodetic sites and global grids with a time resolution of six hours, as well as empirical ("blind") models, such as the Global Mapping Functions (GMF) and the Global Pressure and Temperature (GPT) series, which do not need further input parameters.
The main objective of project Radiate ORD as submission to the Call on "Open Research Data Initiatives" by the Austrian Science Fund (FWF) is to make the current service fully adhere to open access policy. Consequently, Radiate ORD will focus on the consolidation and solidification of all processes necessary to generate and provide the research data following the guidelines of the open access policy. These steps include the improvement and modernisation of the present data flow with stable backup procedures. Furthermore, the interface to the repository of open research data at TU Wien has to be improved, comprising the addition of metadata and the development of clear strategies for versioning and updating the data to allow for full and easy open access.
Beyond that, we will explore the possibility of moving the generation of the VMF1 coefficients to the ECMWF, either as parameters determined a posteriori from archived data or even as regular parameters of the operational runs at ECMWF. We will also add new tools and parameters to the suite of products already existing. For example, we will make our ray-tracing program for the determination of tropospheric delays from numerical weather models openly accessible as web-tool, and we will provide VMF1 coefficients for optical techniques like Satellite Laser Ranging (SLR) to allow for a consistent tropospheric delay modeling across optical and microwave techniques.