Set-up & scientific goals

A Sentinel-5p/TROPOMI validation campaign was held in the Netherlands based at the Cabauw Experimental Site for Atmospheric Research in September 2019. The Cabauw site is part of the Dutch Ruisdael Observatory.

The TROpomi vaLIdation eXperiment (TROLIX) consisted of active and passive remote sensing platforms in conjunction with several balloon-borne, airborne and surface chemical measurements. The goal of this geophysical validation campaign was to make intensive observations to establish the quality of TROPOMI L2 main data products (UVAI, Aerosol Layer Height, NO2, O3, HCHO, Clouds) under realistic non-idealized conditions with varying cloud cover and a wide range of atmospheric conditions. Since TROPOMI is a hyperspectral imager with a very high spatial resolution of 3.6×5.6 km2, understanding local effects such as inhomogeneous sources of pollution, sub- pixel clouds and variations in ground albedo is important to interpret TROPOMI results. Therefore, the campaign included sub-pixel resolution local networks of sensors, involving Pandora and MAXDOAS instruments, around Cabauw (51.97° N, 4.93° E) and within the city of Rotterdam. Cabauw is considered rural while Rotterdam is densely populated and industrialized. These focal areas were connected through airborne as well as ground based mobile observations. Cabauw, using its comprehensive in-situ and remote sensing observation program in and around the 213 m meteorological tower, was the main site of the campaign with focus on vertical proWling using lidar instruments for aerosols, clouds, water vapor, tropospheric and stratospheric ozone, as well as balloon-borne sensors for NO2 and ozone.

The data set collected can be directly compared to the TROPOMI L2 data products, while measurements of parameters related to a-priori data and auxiliary parameters that infuence the quality of the L2 products such as aerosol and cloud proWles and in-situ aerosol and atmospheric chemistry were also collected.

Participating institutes & responsible scientists

  • Royal Netherlands Meteorological Institute, De Bilt, Netherlands (KNMI): Arnoud Apituley (Campaign PI), Marc Allaart, Ankie Piters, Pepijn Veefkind
  • Goddard Space Flight Center, Maryland, United States: Natalya Kramarova, John T. Sullivan
  • Morgan State University Baltimore, Maryland, United States: K. Emma Knowland, Jerry R. Ziemke
  • Belgian Institute for Space Aeronomy Brussels, Belgium: Michel Van Roozendael
  • University of Bremen, Bremen, Germany: Nora Mettiig, Alexei Rozanov, Mark Weber
  • Private company, Germany: Karin Kreher, BK Scientific GmbH

Impressions of the TROLIX Campaign

Scientific output

Sullivan, J. T., Apituley, A., Mettig, N., Kreher, K., Knowland, K. E., Allaart, M., Piters, A., Van Roozendael, M., Veefkind, P., Ziemke, J. R., Kramarova, N., Weber, M., Rozanov, A., Twigg, L., Sumnicht, G., and McGee, T. J.. Tropospheric and stratospheric ozone profiles during the 2019 TROpomi vaLIdation eXperiment (TROLIX-19), Atmos. Chem. Phys., Vol. 22, p.11137-11153, 2022, acp-22-11137-2022.pdf (

An overview of Ruisdael scientific publications can be found here.

Data products and data availability

For specific data products or additional info please contact: Arnoud Apituley – campaign PI (

Ruisdael data storage can be found here.