CESAR Observatory

The Cesar Observatory is located in the western part of the Netherlands (51.971° N, 4.927° E) in a polder 0.7 m below mean sealevel. At the site a large set of instruments is operated to study the atmosphere and its interaction with the land surface.

The Cesar site is used for:

  • Monitoring of long term tendencies in atmospheric changes
  • Studies of atmospheric and land surface processes for climate modeling
  • Validation of space-borne observations
  • The development and implementation of new measurement techniques
  • Training of young scientists at post-doc, PhD and master level.

Three universities and five major research institutes collaborate in Cesar. It is the focal point of experimental atmospheric research in The Netherlands.

If you have any questions about this website or request for additional pages, please contact Henk Klein Baltink at KNMI (henk.klein.baltink@knmi.nl). Also if you are a member of CESAR and don't have the username/password for the member section, please contact Henk Klein Baltink.

A link to the CESAR database portal is listed in the menu on the right hand side.


2019-SEP-23: TROLIX'19 - TROpomi vaLIdation eXperiment 2019

A Sentinel-5p/TROPOMI validation campaign is held in the Netherlands based at the Cabauw Experimental Site for Atmospheric Research during September 2019. The TROpomi vaLIdation eXperiment (TROLIX) consists 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 is 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.

Click here for the campaign website.

2018-SEP-27: Kick-off meeting Ruisdael Observatory

The Ruisdael Observatory ‐ named after the 17th-century painter Jacob van Ruisdael ‐ combines a nationwide dense network of measuring points with high-resolution simulations and the necessary computing power in order to map out changes in local weather, air quality and climate. The official opening of the observatory is on 27th of September, with a meeting at the KNMI measuring station at Cabauw (Cabauw Experimental Site for Atmospheric Research, CESAR). In April 2018 this new top-class research facility was awarded a certificate from NWO’s National Roadmap for Large-Scale Scientific infrastructure. Click here for a news message on the website of the University of Delft.

2017-SEP-01: PICAB Campaign

In September the research group at IMAU organized the Proton-transfer-reaction mass-spectrometer (PTR-MS) Intercomparison campaign in CABauw (PICAB) as part of the European infrastructure program Actris-2. Eleven PTR-MS instruments operated by European and US groups measured for two weeks the ambient air composition at the CESAR observatory near Cabauw. Click here for a news message on the website of the University of Utrecht.

2017-JUN-20: Drone flight at Cabauw

On 21st of June 2017 a drone experiment was performed at Cabauw. Goal was to find out more about application of drones in boundary layer research. A radiosonde was suspended from the drone and during four hours the morning evolution of the boundary layer was observed. A film impression was made by the drone operator (BlikvanBoven). Click here to view the video.

2016-DEC-13: CESAR on NWO roadmap

CESAR is one of the 33 selected Dutch Large Scale Research Facilities placed on the roadmap of NWO (Netherlands Organisation for Scientific Research). State-of-the-Art research facilities significantly contribute to technological and societal innovation. The National Roadmap is about the tools that scientists need to perform their important scientific work for society. It is for good reason that collaboration is one of the Roadmap's cornerstones (see also NWO news item).

2016-OCT-31: CESAR selected as one of thirteen 'Dream facilities' for Scientific Research

The Agenda of the KNAW (Royal Netherlands Academy of Arts and Sciences) is a collection of 'dream facilities' - proposals that could end up on the national or European roadmap for large-scale research facilities in a few years time. The Agenda therefore complements the National Roadmap of the Netherlands Organisation for Scientific Research (NWO). The National Roadmap describes facilities at an advanced stage of planning, with a shorter time horizon to construction.

Countless scientific breakthroughs depend on the availability of advanced research facilities. Such facilities tend to be expensive and take a long time to build. The Royal Netherlands Academy of Arts and Sciences asked researchers to describe 'dream' facilities that they believe could produce scientific breakthroughs in the space of a decade or more. The Academy Agenda for Large-scale Research Facilities is the outcome of that process. (see also KNAW advisory work, and Ruisdael Observatory)

2016-AUG-08: CINDI-2 Campaign 2016

In September 2016, the CINDI-2 campaign will be held in Cabauw. CINDI-2 (Cabauw Intercomparison Campaign of Nitrogen Dioxide measuringInstruments) is a preparatory campaign for the validation of Sentinel-5p/TROPOMI that is scheduled for launch by late 2016. During CINDI-2, additional experiments will also be carried out for the ACTRIS-2 project for light absorption of aerosols and turbulent transport of aerosols. Campaign information is posted on CINDI-2 and the ACTRIS website.

2016-AUG-08: CESAR on National Landscape of Large Research Facilities

CESAR is listed on the Dutch National Landscape of Large Research Facilities of the Netherlands Organisation for Scientific Research (NWO). Click here for the NWO page about CESAR.

2016-FEB-01: CESAR now a certified GRUAN station

GRUAN, the GCOS Reference Upper Air Network (www.gruan.org), is an international reference observing network, designed to fill an important gap in the current global observing system. GRUAN measurements will provide long-term, high-quality climate data records from the surface, through the troposphere, and into the stratosphere. These will be used to determine trends, constrain and calibrate data from more spatially comprehensive observing systems (including satellites and current radiosonde networks), and provide appropriate data for studying atmospheric processes. GRUAN is envisaged as a global network of eventually 30-40 sites that, to the extent possible, builds on existing observational networks and capabilities.

Cabauw is a distributed GRUAN site, together with De Bilt. The radiosondes launched from De Bilt are the first certified data stream to GRUAN. Data streams under development are the ozone sonde, GNSS water vapour columns, Microwave water vapour columns and Raman lidar water vapour profiles. Cabauw/De Bilt is actively involved in the development of these reference quality data products.

2015-JUL-28: TNA ACTRIS-2 now open

The ACTRIS-2 call for Transnational Access (TNA) is now open!

ACTRIS-2 (Aerosols, Clouds, and Trace gases Research InfraStructure) is a European H2020 Project aiming at integrating European ground-based stations for long-term observations of aerosols, clouds, and short-lived gas-phase species. ACTRIS aims to construct a user-oriented research infrastructure in Europe.

ACTRIS-2 provides hands-on access for researchers to CESAR and other world-class observing platforms in Europe. Limited financial support is available to contribute to the travel and subsistence costs of the users. For more information and to apply, please visit the ACTRIS-2 website (click here)

2014-OCT-07: ACCEPT Campaign

During October and the first half of November 2014 the TROPOS institute executes the ACCEPT campaign in collaboration with TU-Delft and KNMI. ACCEPT is performed with support for Trans National Access (TNA) from the ACTRIS project. Click here to visit the ACCEPT weblog.

2014-JUN-02: CESAR flyers

Both an English and Dutch version of the CESAR flyer have been published (click on "other" under "Publications" in menu to download).

2014-JAN-15: Report on 40 year Cabauw research

An overview of research conducted at the Cabauw site in the past 40 years has been published as a KNMI report (click on "reports" under "Publications" in menu to download).

2013-SEP-19: CESAR Science Day 2013

On 19th of June 2013 a CESAR Science Day was organised at KNMI. The presentations and posters have been posted on the website now (click on link in menu section Consortium).

2012-OCT-26: Symposium 40 years Cabauw

In october 1972 the Cabauw mast was officially opened after a few years of preparation and building. For more information click on the link in the menu on the right.

2012-MAY-21: PEGASOS Campaign

In the second half of May 2012 CESAR Observatory is the main focus of the PEGASOS Campaign. Click here to visit the project website.

the 213 m. high meteorological tower

General information

Cabauw 40 year



CESAR Consortium

CESAR Database