Pottiaux, E. ; Bruyninx, C.

Poster presented at BNCGG Study Day “Belgian contributions to Earth Sciences in a Changing World”, Palace of Academy, Brussels, Belgium on 2022-11-04

Abstract: Atmospheric water vapor is a key observation for weather prediction. Global Navigation Satellite Systems (GNSS e.g., GPS, Galileo, GLONASS, Beidou...) are an all-weather observation technique that is capable of precisely and continuously sensing this atmospheric water vapor at a high spatiotemporal resolution. The Royal Observatory of Belgium (ROB) uses GNSS observations to deliver European meteorologists with data collections to improve their weather forecasts. This service is operated 24x7 in the framework of the EUMETNET EIG GNSS Water Vapour Program (EGVAP). However, since its inception, GNSS evolved in a drastically changing landscape, more particularly over the last decade: GNSS has seen the deployment of new constellations, new satellite technologies, the availability of new signals in space, the exponential increase of available ground stations, but also with new, more demanding, user requirements from the meteorological community. All of this increases the potential of GNSS for meteorology but also brings additional scientific and technological challenges and increases the complexity of the task. An example is the use of GNSS to support very-short term weather forecasting. This requires reduced data delivery delay, hence moving towards real-time GNSS data acquisition and processing. In that context, ROB already services the meteorologists with data collections delivered every 15 minutes. To improve further its service, ROB also developed a prototype based on the GNut/Tefnut software from the Geodetic Observatory Pecny (GOP) and participates today in the IAG working group on 4.3.5 “Real-time Troposphere Monitoring”. Another example is to improve the information content that can be retrieved from GNSS observations. This is particularly important during severe weather, but not solely, and this requires the development of a processing technique capable to reconstruct the atmospheric content in the direction of the satellites (gradients and slant delays) and ultimately the 3D water vapor field. In this context, ROB participates in the IAG working group 4.3.6 “Sensing small-scale structures in the lower atmosphere with tomographic principles” and is preparing benchmark data collections that will allow testing different fusion tomography approaches to study the severe floodings that we experienced in July 2021. Similarly, ROB recently delivered a multi-year data collection in the framework of the H2020 ALARM project (https://alarm-project.eu/) to train machine learning algorithms for the forecasting of severe weather initiation to increase aviation safety. Atmospheric water vapor is also the most important natural greenhouse gas as it contributes to about 60% of the natural greenhouse effect and constitutes strong positive feedback to anthropogenic climate forcing from CO2, hence playing a dominant role in the climate change debate and the understanding of the Earth’s climate. In the past, ROB already contributed to climate studies with e.g., the CORDEX.be project (“COordinated Regional Climate Downscaling EXperiment”, 2014-2017, http://cordex.meteo.be/). ROB’s contribution to CORDEX.be was to study and validate the humidity field from 4 Belgian highresolution Regional Climate Models. Today, with almost 30 years of continuous observations at some ground stations, GNSS can today contribute further to climate studies with tailored data collections taking advantage of the latest advances. The length of the time series is close now to the one necessary for climate normals, enabling us to derive statistically significant figures about the climate. The recent increased availability and centralization of accurate meta-information for the ground stations are essential in that context to achieve climate-quality data collections. Harvesting and curating such metainformation for thousands of GNSS stations remains however challenging. This is one of the important missions operated by ROB in the framework of EPOS, the European Plate Observing System. Thanks to this initiative, GNSS observations from more European stations with curated metainformation are available to generate data collections over a longer period, enabling research that goes far beyond the GNSS contribution to CORDEX.be. We are now timely aligned to develop a research infrastructure that can provide FAIR open data collections and scientific services using GNSS for climate research and contribute significantly to the freshly established Belgian climate center. Such infrastructure would enable ROB to sustainably connect at the national level to other Federal Scientific Institutes, Belgian universities, and regional agencies active in the climate domain and at the international level to European and worldwide initiatives like the IAG ICCC (https://iccc.iag-aig.org/), Copernicus Climate Change Service (https://climate.copernicus.eu/)... In this poster, we will summarize ROB’s contributions to GNSS-Meteorology and GNSS-Climate research and services and outline the main perspectives and challenges we are facing.

Keyword(s): GNSS ; Troposphere ; Meteorology ; Climate ; Water Vapour