G2.24   Lack in in-situ calibration of CH4 and CO2 FTIR measurements

Gap detailed description

In-situ calibration of CH4 and CO2 can be performed by aircraft overpasses equipped with in-situ instruments. Such campaigns have been undertaken in the past at many sites, for example as part of IMECC. However, new flight campaigns in Europe are currently not planned and the flights cover only altitude up to about 12 km. Hence the AirCore technique is of great interest to many stations. Total gas column measured by an AirCore sampling system is directly related to the World Meteorological Organization in situ trace gas measurement scales. Therefore the measured AirCore data can be used to contribute to the FTIR calibration (Wunch et al., 2010) and will also provide in-situ data for a more regular validation of ground-based FTIR measurements.

Since Aircore data cover the altitude range up to 30 km, they complement the aircraft campaigns in a very suitable way. Furthermore, the station-to-station bias, which is already quite small, will be further reduced by performing new validation exercises. Understanding and minimizing the bias is essential when studying fluxes from e.g. hot spot regions.

Activities within GAIA-CLIM related to this gap

We propose to perform new AirCore measurements. The AirCore balloon measurements have the benefit of reaching much higher vertical altitudes (up to 30-35 km), compared to the aircraft measurements. In addition, year-round measurements by AirCore are possible. The AirCore method that we propose to use here is a 100 m long coiled sampling tube, with a volume of ≈ 1400 ml (Paul et al., 2016).  The sampling tube is filled during the payload descent and is automatically closed within a short time lag after the landing. The profile analysis can be performed within 2-3 hours after the landing of the payload. Gas analysis can be performed by a Cavity Ring-Down Spectrometer. Within GAIA-CLIM we will be using existing AirCore measurements and also the new AirCore measurements that become available during the project. FTIR data from the AirCore site is obtained simultaneously with the AirCore measurements. The goal is to cover all seasons so that any seasonal differences can be investigated. In addition, we will obtain a larger distribution of measured values due to the existence of a seasonal cycle. The need to perform further aircraft validation flights in combination with these AirCore measurements will be forwarded to the EU, ESA and the national agencies.

Gap remedy(s)

Remedy #1

Specific remedy proposed

Analyse new AirCore measurements. Currently there is a limited availability of AirCore measurements. However, new measurements are envisaged to become available during the project. There are also ongoing activities to simplify and reduce the cost of making the AirCore measurements, thus allowing more sites to participate. The EU, ESA or national agencies should consider arranging dedicated aircraft campaigns for validation purposes in combination with Aircore launches.

Measurable outcome of success

The study would contribute to the next, improved version of the FTIR retrievals and to the assessment of the seasonal cycle. It would also lead to an increased number of AirCore measurements.

Achievable outcomes

Technological / organizational viability: High/mediumThe development is ongoing. The transfer to network management presents some organizational challenges. 

Indicative cost estimate: High (>5 million)/medium (>1million).   This gap has more general nature compared to the prior gap (G2.23) which requires the use of a much larger data sets and hence is leading to an increase in the costs.


The remedy will contribute to the network wide retrieval method. This also helps to address G2.23, by providing more information on accurate profiles in the stratosphere and troposphere.  


2 years

Gap risks to non-resolution

Identified future risk / impact

Probability of occurrence if gap not remedied

Downstream impacts on ability to deliver high quality services to science / industry / society

New data to be used to verify the network wide in situ calibration.


An impact on the traceability to standards.


Work package: