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SPectroscopy In The Far InfraREd: Reducing uncertainties in spectroscopic line parameters for ESA’s FORUM mission (SPITFIRE)



The upcoming ESA FORUM (Far-infrared Outgoing Radiation Understanding and Monitoring) mission will be the first to measure the Earth’s spectrally resolved outgoing longwave radiation in the far-infrared (FIR) at high spectral resolution. This spectral region is responsible for over half of the Earth’s emissions to space, with the principal absorbers being CO2 and H2O. The interpretation of the FORUM measurements is reliant on the ability to perform accurate radiative transfer calculations in the FIR. However, the spectroscopic linelists currently available in the FIR, especially for water vapour, have large uncertainties. In this project, a novel approach to measuring spectra in the FIR region will be used. Synchrotron light source facilities will be utilised to measure high-resolution, high signal-to-noise spectra of both CO2 and H2O across the entire FIR region. Non-Voigt line parameters, as well as line mixing using the full relaxation matrix approach, will be derived using the Labfit program, with the aim of simulating spectra with an overall uncertainty of ~1%, far better that currently possible using the Voigt parameters from the High resolution TRANsmission (HITRAN) database. Existing ground-based and aircraft measurements, and data from the Infrared Atmospheric Sounding Interferometer (IASI) instrument, along with new data from the UNiversal InfraRed Airborne Spectrometer (UNIRAS) instrument, will be used to test the new spectroscopic parameters. Furthermore, the new parameters will be used to simulate clear-sky estimates of spectral radiative forcing, and compared with simulations using older spectroscopy. Ultimately, these line parameters will improve atmospheric radiative transfer modelling required for the upcoming Far-infrared Outgoing Radiation Understanding and Monitoring (FORUM) mission. This mission aims to improve the accuracy of climate change forecasts, which will prove crucial in future efforts to mitigate against climate change.


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