Monitoring the composition of the Earth's atmosphere
Scientist satellite remote sensing at KNMI

On 1 June 2011 I returned to the Royal Netherlands Meteorological Institute (KNMI), after having been there during 1999-2004 and at the Belgium Institute of Space Aeronomy (BIRA-IASB) during 2004-2009.
The research division I am in at KNMI is called Satellite Observations.
[instrument logo] [satellite logo]

The satellite instrument TROPOMI ("Tropospheric Monitoring Instrument") has been developed by industrial parties and was launched on 13 October 2017 on board of the European GMES Sentinel-5 Precursor satellite, and will act as the successor of OMI ("Ozone Monitoring Instrument") aboard the NASA satellite EOS-Aura (2004-present). KNMI has the scientific lead for the TROPOMI instrument and fulfils the role of Principal Investigator (PI) institute for this international mission, as it also does for OMI.
[measuring satellite] The TROPOMI mission objective is to monitor the troposphere for scientific research and in support of services to society. Measurements are taken down to the Earth's surface with sufficiently high resolution in both space and time, in order to be able to quantify anthropogenic and natural emissions, and to quantify atmospheric life cycles of trace gases and aerosol particles which have an impact on air quality and climate forcing from the regional to the global scale.
[OMI logo] For this TROPOMI mission I play a role in the team that works on the definition and development of the TROPOMI algorithms for trace gas, aerosol and cloud data products, and of the operational TROPOMI software. In addition to the development of new algorithms, this team also maintains and improves existing algorithms for OMI -- in close collaboration with the teams working with data from other satellite instruments (GOME-1, SCIAMACHY, GOME-2). Meanwhile we are already making preparations for the successor of TROPOMI: the Sentinel-5 instrument to be launched in 2022-23.

See for more information on the main projects:
[NO2 mean over Europe sept 2011]

Nitrogen dioxide (NO2)

My main focus is the algorithm for the retrieval of concentrations of nitrogen dioxidd (NO2), a key element of air quality issues -- NO2 in the atmosphere originates from anthropogenic (i.e. man-made) sources and from natural processes: fossil fuel combustion, biomass burning, soil release, lightning, etc.
The image on the right shows the NO2 concentration in the troposphere over Europe as derived from OMI measurements, averaged over September 2011.
[Source: TEMIS website]
[QA4ECV logo] For TROMOPI and Sentinel-5 my work involves development of the algorithm, based on an existing NO2 algorithms used for other instruments. This work is done in close with researchers from other institutes and within the framework of international projects. The work on NO2 is also connected to the QA4ECV project.

See for more information on NO2, data and maps the TEMIS website.

[UV index of 16 July 2016]

UV index & UV dose

Since the second half of 2015 for a small part of my time I returned to an old favourite: UV index and UV dose data as well as UV index forecast worldwide, based on satellite observations of ozone.

It was time to implement a few improvements to the data processing system: higher spatial resolution, more recent background input data, improved cloud correction, improved error estimates, etc., thus created dataset version 2.0.

The image on the left shows the UV index over Europe as derived from ozone measurements of the GOME-2 instrument. [Source: TEMIS website]

My task in this is to ensure that the processing of the UV data continues, to answer questions we get and to provide data to other researchers who which to use the data for their research, e.g. studies into health issues related to vitamin-D and UV radiation. The UV index forecast we provide is used by KNMI to provide the official UV index ("zonkracht" in Dutch) forecast for The Netherlands.


[DOAS Workshop 2020 cover]

DOAS Workshop 2020

In 2020 I am involved in the organisation of the 9th International DOAS Workshop, held in Utrecht.

For more information, see the DOAS Workshop 2020 website.


[cover of module document]

Educational material

In 2015-16 I have also made a large contribution a module for secondary schools on "Satellites and Earth Observation", notably to the section on Atmosphere, regarding aerosols, ozone and UV radiation at the surface.
This module -- which is, of course, in Dutch -- can be found at this webpage; the cover of the module is shown on the right. Two web pages, also in Dutch, with some additional information are used in this describe from spectrum to ozone to UV index and UV index & UV dose time series.
Furthermore I have contributed to the educational material made by KNMI in relation to the GLOBE Aerosol activities (see below). And I have contributed to material for "Earth Observation and Climate" workshops KNMI occasionally gives for schools, e.g. in the country-wide framework of science activities schools ("Wetenschapsweek" and such).

[AOT in Utrecht 14 Sept. 2016]

Aerosol measurements with Calitoo sunphotometer

The Calitoo sun photometer is a hand-held device to measure direct sunlight and from that derive the aerosol optical thickness (AOT; also known as the aerosol optical depth, AOD) at blue, green and red wavelengths (465, 540 and 619 nm).

In our group we have bougth a few Calitoo's and we are using these to measure the AOT in several places, when one of us travels to some place or during campaigns. For the moment this is done ad-hoc. My involvement in this is handing out the instruments and gathering the AOT data.

The image on the left shows measurements of the AOT performed from my balcony in Utrecht on a very sunny (and very warm) day.

[GLOBE program]

GLOBE project

In addition during 2011-2015 I have played a supportive role in the KNMI contribution to the international GLOBE project regarding the topic "measurements of aerosol concentrations", helping e.g. with processing the data.
The Global Learning and Observations to Benefit the Environment (GLOBE) program is a worldwide hands-on, primary and secondary school-based science and education program. GLOBE's vision promotes and supports students, teachers and scientists to collaborate on inquiry-based investigations of the environment and the Earth system working [...] in study and research about the dynamics of Earth's environment.

[Source: The GLOBE program website]
Aerosols are small particles (dust, sand, etc.) and droplets floating in the air. Aerosols contribute to the greenhouse effect and climate change, and they can cause breathing problems. For this reason aerosol concentrations are monitored by satellite and ground based instruments. Within GLOBE pupils can contribute to the understanding of aerosol concentrations by taking daily measurements of the sunlight.

For GLOBE Netherlands KNMI used to coordinate the aerosol measurements and used the data for comparisons with satellite measurements. Since 2015 KNMI unfortunately has no financial means to continue this contribution, as a result of which my contribution has ended too.

See for more information on GLOBE:


===> list of my publications about my post-doc. positions in atmospheric research.

See a separate page for the meaning of some acronyms.  

Place of work
[KNMI logo]
Royal Netherlands Meteorological Institute (KNMI)
Climate Research and Seismology Department
Satellite Observations Devision
P.O. Box 201
3730 AE   De Bilt
The Netherlands
visiting address:   Utrechtseweg 297, De Bilt
[KNMI logo]
By the way:
During the period June 2011 - May 2014 I was officially not employed by KNMI itself but by the KNMI-operated Stichting Wetenschappelijk Onderzoek (SWO; "Foundation for Scientific Research" in English).
Since 2 Sept. 2014 I am employed by KNMI -- via the Ministery of Infrastructure and Environment, of which KNMI is part (for contractual reasons there had to be a gap between the contracts).
[SWO logo]

Jos van Geffen -- Home  |  Site Map  |  Contact Me

created: 26 May 2011
last modified: 10 February 2021