Instruments location and measurements techniques

Retrieval methods

Measurements campaigns

Laboratory support

 

 

 

 


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Last update: September 2009

Instruments location and measurements techniques:

Past and/or current observations performed by the following instruments operated by the AGACC partners will be used in the present project:






Jungfraujoch (46.5°N, 8°E)
primary NDACC Alpine station

  • High-resolution Fourier Transform Infrared (FTIR) spectrometer
  • UV/Visible spectrometer using the Multi-Axis Differential Optical Absorption Spectroscopy (MAXDOAS)


Ile de La Réunion
(21°S, 55°E) complementary NDACC station

  • High-resolution Fourier Transform Infrared spectrometer
  • UV/Visible spectrometer using the Multi-Axis Differential Optical Absorption Spectroscopy (MAXDOAS) method
  • CIMEL sun photometer





Uccle/Ukkel (50.5°N, 4°E)
complementary NDACC station

 

 

 

  • High-resolution Fourier Transform Infrared spectrometer
  • UV/Visible spectrometer using the Multi-Axis Differential Optical Absorption Spectroscopy (MAXDOAS) method
  • Radio (PTU) soundings
  • Two Brewer ozone spectrophotometers
  • CIMEL sun photometer

 
* At Ile de la Réunion, it is planned to have access to an NDACC infrastructure at the Maido site, at about 2200 m asl, from 2009 onwards. Up to that time, only campaign data will be available.

* The CIMEL sun photometers, are part of the worldwide AERONET program (AErosol RObotic NETwork), the goal of which is to assess aerosol optical properties and validate satellite retrievals of them.

* High-resolution Fourier Transform Infrared spectrometers are also used in the laboratory.



Maximum advantage will be taken from the complementary geophysical information provided by these various instruments and techniques:


• Spectra recorded by the FTIR instruments encompass characteristic absorption features of most target gases, allowing to determine their total column abundances and, in several instances, information about their vertical distribution in the atmosphere . The unique capability to measure isotopic species in these spectra will be exploited here for a better understanding of the chemical and dynamical processes affecting some of the target species;

• The UV-visible DOAS technique is widely used to monitor the stratospheric column amount of several important trace gases (e.g., O3, NO2, BrO, OClO). With the recent development of the Multi-Axis DOAS technique new capabilities have been demonstrated to perform partial column measurements of H2CO from the boundary layer up to the free troposphere. Based on measurements of the O2-O2 absorption, the same technique can also be used to infer vertically resolved information on aerosol properties in the 0-3 km altitude range;

• The radio (PTU) soundings at Uccle will be used here to determine long time series (starting in 1990) of atmospheric relative humidity profile data with high time and vertical resolution;

Total Aerosol Optical Depth (AOD) in the UV-B range can be derived from Brewer observations performed at Uccle on a daily basis, allowing to study the diurnal, seasonal and inter-annual variations and trend of AOD in the atmosphere over a long time period. These values are directly linked to the quantity of aerosol in the atmosphere, as they represent the extinction of the incoming solar radiation by aerosol particles;

Sun photometer observations yield very precise (1%) values for AOD; information on the scattering phase function can also be derived. From these quantities, information on the aerosol size distribution, the single scattering albedo and the refractive index can be extracted. In addition, the total atmospheric columnar water vapour content can be derived with a precision of the order of 2-3%. Within this project, AOD measurements performed with the CIMEL will be used as a reference;

FT spectroscopy (FTS) is a widely used technique for laboratory studies. Its main advantages lie in very high-resolution, accurate and reproducible frequency determinations, simultaneous sampling of all wavelengths, and capability of absolute line intensitiy determinations. The tunable diode laser spectroscopy technique, offering specific advantages such as high sensitivity and short response time, will complement FTS measurements, when necessary. The targeted species will be, on one hand, water vapour and monodeuterated water (HDO), and on the other hand, carbon species, namely C2H2, 13CO and H2CO.


Retrieval algorithms:

Specific advanced retrieval algorithms available to the consortium will be used to extract the most pertinent information from all the various observational data sets available. In particular:

• Within the ESAC-II project, KMI-IRM developed an algorithm to retrieve the total AOD from Brewer observations in the UV-B range. This algorithm will be applied to to regular observations.

SFIT-2 is the NDACC recommended algorithm to analyze high-resolution FTIR spectra. It is based on the Optimal Estimation Method (OEM) and allows extracting and characterizing information on the vertical distribution of many FTIR target gases. AtmosPhit is a retrieval program developed at the ULB, similar to SFIT-2, and validated, but with some distinct features. AtmosPhit will be used in the frame of this project as a research tool for detailed scientific studies, in particular for the FTIR water vapour soundings. Software complements to AtmosPhit and SFIT-2 are available for performing direct characterization of the retrieved quantities (vertical information contents and error budgets).

WINDOAS is a multi-purpose DOAS retrieval algorithm developed at BIRA-IASB in the late '90s. It is based on a coupled linear/non-linear least-squares (NLLS) fitting algorithm that allows to derive integrated slant column abundances for a series of trace gases having structured absorption features in the UV-Visible range (300-600 nm). It has been validated on several instances through participation in intercomparison exercises and is currently widely used as a standard software package within the NDACC and the international DOAS research community.

• As a complement to the WINDOAS program, an algorithm to extract and characterize information on the vertical distribution of some trace gases (NO2, BrO) has been developed and validated within the project ESAC-II. It is based on Optimal Estimation. Within the AGACC context, it will be used and adapted to derive H2CO partial columns and aerosol properties.

• The CIMEL is a calibrated photometer that measures the optical density of the atmosphere based on observations of the direct solar irradiance in various channels from 300 up to 1050 nm. In the aerosol reference channels (440, 670, 870 and 1020 nm) the aerosol optical density (AOD) is easily derived after correction for the known contribution from Rayleigh scattering. In addition, sky radiance observations are performed away from the sun through a large range of scattering angles (20 to 120), which provide additional parameters like aerosol size distribution, phase function and aerosol optical thickness.


Measurements campaigns:

  • Ile de la Réunion campaign (June 2009 - December 2009): currently ongoing...
  • Ile de La Réunion campaign (May 2007 - November 2007)
  • Uccle/Ukkel campaign (July 2006 - April 2007): participation of CIMEL, FTIR, MAXDOAS instruments and observations at IRM/KMI.


Analyses are ongoing



Laboratory support:

For more information on our laboratory work, please follow this link: BIRA-IASB Spectroscopy Lab