The VAPOUR Project
The VAPOUR project will provide the next generation, space-geodetic, high-quality, spatiotemporal, asymmetric (Slant Total Delay (STD) in addition to legacy Zenith Total Delay (ZTD) and gradients (GRD)) tropospheric products, to improve numerical weather prediction (NWP) models for forecasting and derived re-analysis models on national and international levels. VAPOUR will employ Global Navigation Satellite System (GNSS) observations, including those of the European Galileo, and Synthetic Aperture Radar Interferometry (InSAR) data, such as from the Copernicus Sentinel missions.
The advanced products will take better account of the distribution of atmospheric water vapour within the troposphere, which is the most prominent greenhouse gas and is directly linked to precipitation and weather. Most current GNSS-derived tropospheric products do not fully account for these variations or suffer from unresolved issues such as multipath and the development of such products from SAR data is still largely experimental.
With the interest of the meteorological services for these products growing, VAPOUR is timely and highly relevant. As current ZTD products lack the horizontal resolutions required, VAPOUR will seek to improve and refine the STD and GRD products through the analysis of multi-GNSS receiver-to-satellite line-of-sight (slanted-anisotropic) delays which offer a much higher spatial resolution but also suffer from site-specific errors such as multipath. VAPOUR will improve the reconstruction of the short-term slant water vapour fluctuations through innovative approaches to multipath mitigation using multi-GNSS high-precision solutions.
Also the signals from SAR satellite missions are subject to delays in the atmosphere. Most studies consider the delay experienced by SAR signals as a nuisance parameter and correct it by complicated modelling approaches. Instead, VAPOUR will derive maps of water vapour fields from these radar data and will employ these for cross- evaluations with the GNSS-derived fields.