Ground based measurements

Our measurement sites

Our team is responsible for or participates in FTIR measurements in 3 locations...

Our team is responsible for FTIR measurements in 1 location (St Denis, Ile de la Réunion), and participates in the measurements performed by ULg in the second location (Jungfraujoch, Switzerland). The third location (Uccle, Belgium) is used as a test site by our team. These three measurement sites are all part of the NDACC network.

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Ile de la Réunion (21° S, 55° E):

Ile de la Réunion is an island situated in the Indian Ocean, near Madagascar, East from the African Continent, and is French territory. It is one of the very few NDACC stations at southern (sub)tropical latitudes.

Measurements have been performed at St Denis (50 m asl) and at the Maido site (2203 m asl).


This second site is not fully operational yet, but we have already organized a campaign there in 2002. The advantage of such a high altitude site, above the boundary layer, is a lesser degree of interfering humidity and pollution, which improves the quality of our measurements.

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Since September 2009, our FTIR observations at Ile de la Reunion have been officially accepted as NDACC measurements. This means that the quality of the observations and of the derived geophysical data comply with the quality standard defined by the NDACC Infrared Working Group. Therefore, the data are submitted to the NDACC archive. See the NDACC website for more details.

Jungfraujoch (46.5°N, 8°E):


This station is situated in the Swiss Alps, at 3580 m above sea level. We collaborate there with the University of Liège (ULg). They are responsible for the FTIR instruments at Jungfraujoch.

The GIRPAS group from University of Liege has started the first measurements there in 1950! The very long time series help us to study the evolution of several compounds present in our atmosphere, and to analyse the impact of recent human activity. Visit the GIRPAS website for more information.


Test site: Uccle (50°N, 4°E):

Uccle is our home station where we test new instruments and tools, accessory material, home built suntracker and automatization systems like BARCOS.

containerUccle ozone.meteo
Our container with inside the
recently bought Bruker 125HR instrument.

The species we detect

With our FTIR instruments, we detect following types of species...

Direct greenhouse gases: Other species:
Methane (CH4) Carbon monoxide (CO)
Nitrous oxide (N2O) Ethane (C2H6)
Ozone (O3) Hydrogen cyanide (HCN)
Water Vapour (H2O) Formaldehyde (CH2O)
Carbon Dioxide (CO2) Nitric acid (HNO3)
  Hydrogen chloride (HCl)
  Hydrogen fluoride (HF)

More details on these species can be found here.

Reactive inorganic chlorine plays a crucial role in the stratospheric ozone depletion. Some examples of important chlorinated source gases are CFCs, HCFCs, CCl4, CH3CCl3 and Halons. These source gases are photolysed in the stratosphere into inorganic chlorine and fluorine.

Our instruments

The instruments we use are Fourier Transform (FTIR) spectrometers...


They are Michelson type interferometers. They employ the mathematical concept of Fourier series analysis as a means of converting a detector signal output – referred to as the interferogram – into a form useful for spectral analysis.

The incoming light is split into two different optical paths. The light intensity at the detector – after recombination of the light from the two individual paths-, is recorded as a function of the displacement of the movable mirror in one of the light paths, which modulates the radiant intensity I (λ) as a function of mirror distance. The intensity distribution captured by the detector is referred to as the “interferogram” (representing the sum of all modulated waves). The interferogram is not directly usable; it requires a Fourier transformation to obtain the spectrum.

Our team uses 2 types of FTIR spectrometers from the Bruker company: the Bruker IFS 120M and the Bruker IFS 125HR. The Bruker 120M at Ile de La Reunion shall soon be replaced by a Bruker 125HR which delivers data at higher resolution.

In addition, a second Bruker 125HR will be installed for the dedicated measurement of greenhouse gases, in particular CO2 and CH4.

bruker 120 FTS
bruker 125 HR

In the diagram hereafter, you can see how the light beam is directed in this spectrometer

Copyright © Brukeroptics


Automation tool: BARCOS

BARCOS is an automation and remote control system for atmospheric observations with a Bruker interferometer, developed at BIRA-IASB...

It includes specific software (written in Labview), a suntracker and a meteostation.


  • Enables us to perform the operation of the spectrometric atmospheric observations in a remotely controlled or autonomous way, without human presence at the measuring site.
  • Is built with existing commercial hardware and software components, including the Bruker OPUS software for the operation of the spectrometer.
  • Includes a small meteorological station and a suntracker.
  • Is a flexible system, allowing manual interventions at any time.
  • Is operational with access to the internet at the site of operation.

The detailed description of the BARCOS system hardware and software configurations can be consulted in the publication BARCOS, an automation and remote control system for atmospheric observations with a Bruker interferometer.



We have performed 3 FTIR measurement campaigns...


At Ile de la Réunion, we have performed 3 FTIR measurement campaigns in collaboration with ULB and LACy (OPAR)

  • October 2002
  • August-October 2004
  • May-November 2007

Our technicians, engineers and scientists have been working hard to finalise the installation of our instrument.

Since June 2009, continuous measurements are running at St Denis.  

In the near future, we plan to install a new instrument at the high altitude Maido site.





  • NDACC: Network for the Detection of Atmospheric Composition Change
  • TCCON: Total Carbon Column Observing Network


Thanks to the quality of our FTIR measurements at Ile de la Réunion, we are certified members of the Network for the Detection of Atmospheric Composition Change (NDACC) Infrared Working Group.

The St Denis site at Ile de La Reunion hosts several other qualified NDACC instruments.

The two other stations where we work (Jungfraujoch and Uccle) are also recognized NDACC stations hosting several certified atmospheric monitoring experiments. 

NDACC: Network for the Detection of Atmospheric Composition Change 


This is a global network of ground-based Fourier Transform Spectrometers recording direct solar spectra in the near-infrared spectral region.

From these spectra, very accurate and precise total columns of CO2, CH4, N2O, HF, CO, H2O, and HDO are retrieved. TCCON provides an essential validation resource for SCIAMACHY, GOSAT, and the future OCO-2.

Our objective is to become member of this network with FTIR greenhouse gas measurements at St Denis - Ile de la Réunion.

TCCON: Total Carbon Column Observing Network


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