The aim of our proposal is to perform an intercomparison of measured total column concentrations of a few GHG using several different spectroscopic instruments at a TCCON site. The measurements will be supported by an insitu balloon system which measures the vertical concentration profile of the trace gases, and which can be calibrated relative to the WMO standards.
The measurement campaign is planned to take place in Sodankyla/Finland in 2017. The Finnish subcontractor (FMI) runs there a TCCON instrument and has experience with AirCore launches since September 2013. FMI also runs a PICARRO G2401 system which is needed to analyse the AirCore sample after landing. We plan to bring five different spectrometers, working with different resolution and different techniques (Michelson interferometer, grating spectrometer, and a laser heterodyne spectrometer). The AirCore system and data analysis, sampling the atmospheric concentration profile up to 30 km, will be supported by the Dutch (University of Groningen) subcontractor.
The intercomparison between all instruments will be done in a first step in a quasi-blind approach, i.e. each partner carries out the measurements and retrieval independently for his instrument; then another partner carries out the intercomparison between the results. Following this first exercise, AirCore data will be included as a-priori information in the retrieval process. The whole retrieval will be repeated to study the impact of the vertical concentration profile on the results and intercomparison. Observed differences between the data will be discussed on a regular basis with the partners and the measurement specifics are modified if necessary. Measurements and analysis will then be continued to get more statistically significant results, and study the seasonal impact (e.g. by humidity and solar zenith angle) on the results.
As an optional activity to the IR instruments intercomparison, depending on funding, the development of an improved AirCore gliding system for calibrating ground-based IR instruments and satellite retrievals will be investigated.
Numerous stakeholders will benefit from our campaign. On one side, the satellite community needs to know which instruments are suitable for future validation campaigns. Since the global coverage of TCCON is very limited, more validation sites in areas with limited and difficult access are required. This includes for example sites with high albedo in the Himalaya or in desert regions of the Earth, where the large TCCON instruments are difficult to be installed. Here a small instrument will be the only possibility to perform validation campaigns. Satellites of interest are: GOSAT, OCO-2, all future Sentinel ESA instruments, as well as the Chinese Tansat mission, and possibly the Merlin and Microcarb missions. Furthermore, we suggest using the acquired data within the S5P validation efforts through the AOs in which the team is involved, depending on national funding.
Finally, our results will be of importance for the modelling community. Inversion models, to retrieve the sources and sinks on a regional or global scale, require observational data as input for the models. Our campaign will also be of interest for the industry, building analytical instruments for the environment. Climate change has become an important commercial issue. Our studies will be of importance for the industry to decide which kind of instrumentation might be produced for a larger market. The exchange and cooperation with existing networks and initiatives as well as the feedback from the satellite teams constitute an important objective to ensure that the outcome is also taken into account by all stakeholders. This implies continuous interfacing with TCCON and NDACC, specifically the Infrared Working Group (IRWG). Further, the satellite retrieval and validation teams will be involved to ensure that the project results can directly be applied to the satellite product characterization. All project activities shall follow the overarching principles of QA4EO. This shall be intrinsic to all applicable project tasks, also in case QA4EO is not specifically mentioned in all requirements.
Technical details about the instrumentation and the site has been discussed in details in the deliverable reports.