|Logo of project GGOS Atmosphere|
In recent years, models for atmosphere-related effects in space geodesy — such as troposphere delays, pressure loading, gravity corrections, or excitation of Earth rotation — have been developed which are based on data from numerical weather models. However, the parameters describing each of these phenomena have been determined at various institutions, using different weather model data, and applying varying geophysical hypotheses. Project GGOS Atmosphere reconciles these efforts by determining consistent and homogenous estimates for atmosphere angular momentum, troposphere delays, gravity field coefficients, and pressure loading corrections based on a common data stream with predominantly the same underlying meteorological parameters. As such, "GGOS Atmosphere" represents also a generic term for projects ASPIRE and RADIATE VLBI, which are devoted to specific parameter groups (angular momentum and delays) and their relevance for space geodesy.
|Logo of project ASPIRE|
Short period variations of Earth rotation are subject to a small but perceptible influence from atmospheric dynamics and pressure-driven oceanic mass-field variability associated with diurnal and semidiurnal radiational atmospheric tides. Preceding studies of these intriguing effects have however failed to provide reliable rotational estimates and a complete picture of related dynamical processes in the Earth system. Project ASPIRE (Atmosphere-Induced Short Period Variations of Earth Rotation) attempts to redress this shortcoming by applying two equivalent modeling methods (diagnosis of angular momentum variations, analysis of Earth-atmosphere-ocean interaction torques) in parallel and thus assessing the reliability of excitation measures as computed from present-day atmospheric analysis systems. Conceptualized as a joint international project with GFZ (Geoforschungszentrum) Potsdam, ASPIRE also utilizes a state-of-the-art ocean model to conduct consistent angular momentum/torque considerations for the oceans.
|Logo of project RADIATE VLBI|
Tropospheric delay modeling is the major error source in the analysis of geodetic VLBI observations, and in order to comply with the ambitious GGOS accuracy goals of 1 mm in position and 0.1 mm/year in velocity for the terrestrial reference frame, it is imperative to improve existing tropospheric correction models. The determination of slant delays by ray-tracing through high-resolution data from numerical weather models is the most rigorous approach possible today, suited to replace conventional mapping function strategies in VLBI data analysis. Project RADIATE VLBI aims to determine ray-traced delays for the whole history of about five million geodetic VLBI observations since 1979 from operational analysis and re-analysis data of the European Centre for Medium-range Weather Forecasts (ECMWF) as well as for all upcoming VLBI observations from forecasting data to have the delays available in real-time.