Atmospheric radition explorer in the far infrared
The atmosferic Radiation Explorer in the Far InfraRed) experiment concerns the exploitation of the broadband spectrally-resolved measurement of the radiation emitted by the Earth and the atmosphere over the relevant spectral region from the mid-infrared (MIR), from 500 to 1600 cm<sup>-1</sup> (wavelength = 20 – 6.25 µm) to the under-explored far-infrared (FIR) region, from 100 to 500 cm<sup>-1</sup> (wavelength = 100-20 µm), with the aim to improve the characterisation of the chemical-physical processes involved in the greenhouse effect and the Earth Radiation Budget (ERB).
The specific scientific objectives that drive the experiment are:
1. the study of the spectrally-resolved OLR and DLR (Outgoing and Downwelling Longwave Radiation) for the accurate identifications of the climate “fingerprints” and their attribution to the underlying atmospheric processes;
2. the determination of the atmospheric state, improving in particular the measurement of the water vapour profile in the upper troposphere using the FIR observations;
3. the improvement of thin cloud characterisation, such as high-altitude cirrus clouds, using the new information from the FIR region, and the assessment of their longwave contribution to the Earth radiation budget.
Field measurements have been performed by the REFIR-PAD (REFIR – Prototype for Applications and Development) prototype since 2005 from both stratospheric balloons (OLR measurement from 34 km of altitude) and high-altitude ground-based sites (DLR measurements from altitudes in the range of 3,000 – 5,000 m). Recently, REFIR-PAD has been permanently installed at the Italian-French base of Concordia over the Antarctic Plateau at Dome-C at 3,230 m of altitude (http://refir.fi.ino.it/refir-pad-domeC) , where it has been supplying spectral observations of the DLR components with automatic operations since the December 2001. These observations are of particular interest since they cover for the first time the FIR spectral region with systematic measurements under all sky conditions.
The data archive is at the web page http://refir.fi.ino.it/rPADdata/
These spectral measurements, together with other auxiliary data gathered by co-located instrumentation, supply an unique and innovative dataset that will allow to improve the characterisation of the main atmospheric components of the Earth radiation budget, such as the upper tropospheric water vapour and thin clouds.
Finally, the developed prototype and the performed field measurements will supply the background experience for the design and the proposal of new space missions able to cover the FIR observational gap of the thermal radiation emitted by the Earth towards the space.
In particular, in 2017 the European Space Agency (ESA) selected the FORUM mission (Far-infrared Outgoing Radiation Understanding and Monitoring), proposed by INO, as a candidate for the Earth Explorer 9. Also in 2017, the Italian Space Agency ( ASI) funded the SCIEF study (Development of the Italian Skills for the FORUM Experiment) to support national studies in defining the measurement requirements of the FORUM mission.
The feasibility study is underway with the ESA FORUMreq and FIRMOS projects which will lead to the definition and consolidation of the observation requirements of the space mission whose final selection will be decided at the User Consultation Meeting in July 2019. Within these projects, coordinated by INO, a new FTS prototype operating in the FIR, called FIRMOS, was also developed and tested in the measurement campaign by the Zugspitze Siummit in Germany at an altitude of about 3000 m. More information about the activities connected to the FORUM mission is available at https://www.forum-ee9.eu/