Articles | Volume 9, issue 7
Atmos. Meas. Tech., 9, 2989–3008, 2016

Special issue: Advanced Global Navigation Satellite Systems tropospheric...

Atmos. Meas. Tech., 9, 2989–3008, 2016

Research article 14 Jul 2016

Research article | 14 Jul 2016

Benchmark campaign and case study episode in central Europe for development and assessment of advanced GNSS tropospheric models and products

Jan Douša1, Galina Dick2, Michal Kačmařík3, Radmila Brožková4, Florian Zus2, Hugues Brenot5, Anastasia Stoycheva6, Gregor Möller7, and Jan Kaplon8 Jan Douša et al.
  • 1NTIS – New Technologies for the Information Society, Geodetic Observatory Pecný, RIGTC, 25066 Zdiby, Czech Republic
  • 2Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences, 14473 Potsdam, Germany
  • 3Institute of Geoinformatics, VŠB – Technical University of Ostrava, 70833 Ostrava, Czech Republic
  • 4Numerical Wheather Prediction Department, Czech Hydrometerological Institute, 14306 Prague, Czech Republic
  • 5Atmospheric Composition Department, Royal Belgian Institute for Space Aeronomy, 1180 Brussels, Belgium
  • 6Forecasts Department, National Institute of Meteorology and Hydrology, 1784 Sofia, Bulgaria
  • 7Department of Geodesy and Geoinformation, TU Wien, 1040 Vienna, Austria
  • 8Institute of Geodesy and Geoinformatics, Wroclaw University of Environmental and Life Sciences, 50–357 Wroclaw, Poland

Abstract. Initial objectives and design of the Benchmark campaign organized within the European COST Action ES1206 (2013–2017) are described in the paper. This campaign has aimed to support the development and validation of advanced Global Navigation Satellite System (GNSS) tropospheric products, in particular high-resolution and ultra-fast zenith total delays (ZTDs) and tropospheric gradients derived from a dense permanent network. A complex data set was collected for the 8-week period when several extreme heavy precipitation episodes occurred in central Europe which caused severe river floods in this area. An initial processing of data sets from GNSS products and numerical weather models (NWMs) provided independently estimated reference parameters – zenith tropospheric delays and tropospheric horizontal gradients. Their provision gave an overview about the product similarities and complementarities, and thus a potential for improvements of a synergy in their optimal exploitations in future. Reference GNSS and NWM results were intercompared and visually analysed using animated maps. ZTDs from two reference GNSS solutions compared to global ERA-Interim reanalysis resulted in accuracy at the 10 mm level in terms of the root mean square (rms) with a negligible overall bias, comparisons to Global Forecast System (GFS) forecasts showed accuracy at the 12 mm level with the overall bias of −5 mm and, finally, comparisons to mesoscale ALADIN-CZ forecast resulted in accuracy at the 8 mm level with a negligible total bias. The comparison of horizontal tropospheric gradients from GNSS and NWM data demonstrated a very good agreement among independent solutions with negligible biases and an accuracy of about 0.5 mm. Visual comparisons of maps of zenith wet delays and tropospheric horizontal gradients showed very promising results for future exploitations of advanced GNSS tropospheric products in meteorological applications, such as severe weather event monitoring and weather nowcasting. The GNSS products revealed a capability of providing more detailed structures in atmosphere than the state-of-the-art numerical weather models are able to capture. In an initial study on the contribution of hydrometeors (e.g. cloud water, ice or snow) to GNSS signal delays during severe weather, the effect reached up to 17 mm, and it was suggested that hydrometeors should be carefully accounted for within the functional model. The reference products will be further exploited in various specific studies using the Benchmark data set. It is thus going to play a key role in these highly interdisciplinary developments towards better mutual benefits from advanced GNSS and meteorological products.

Short summary
GNSS products provide observations of atmospheric water vapour. Advanced tropospheric products focus on ultra-fast and high-resolution zenith total delays (ZTDs), horizontal gradients and slant delays, all suitable for rapid-cycle numerical weather prediction (NWP) and severe weather event monitoring. The GNSS4SWEC Benchmark provides a complex data set for developing and assessing these products, with initial focus on reference ZTDs and gradients derived from several NWP and dense GNSS networks.