1,1,2,3,5- 1Department of Physics, Imperial College London, London, UK
- 2NERC National Centre for Earth Observation, Imperial College London, London, UK
- 3Department of Atmospheric and Oceanic Sciences, University of Wisconsin, Madison, WI, USA
- 4Space Science and Engineering Center, University of Wisconsin, Madison, WI, USA
- 5European Centre for Medium-Range Weather Forecasts, Reading, UK
Despite containing up to half of the Earth’s thermal emission to space, the far-infrared spectral region (FIR, defined here as 100–667cm-1 or 15–100µm) has rarely been observed from satellites. Spectrally-resolved measurements, which offer a deeper understanding of the observed physical processes, have been limited to a 9-month dataset from 1970. This has led to substantial uncertainties in the spectroscopy of water vapour, radiative properties of clouds, and the surface spectral emissivity; these in turn limit confidence in modelled FIR energy flows.
With the advent of the Polar Radiant Energy in the Far-InfraRed Experiment (PREFIRE), we have made a step towards the return of spectral measurements of the Earth in the FIR. Launched as a NASA Earth Venture mission in 2024, it consists of two polar-orbiting CubeSats equipped with uncooled grating spectrometers. The instruments offer a new perspective of the Earth with a moderate spectral resolution. However, there remains some uncertainty regarding their calibration.
To this end, we attempt to assess the accuracy of PREFIRE spectral measurements by way of a ‘ground-to-space’ closure experiment. Using zenith-viewing observations from the ground-based Far INfrarEd Spectrometer for Surface Emissivity (FINESSE), for which uncertainties have been thoroughly characterised, we gauge the representativity of atmospheric data from radiosonde launches and reanalysis. Using these data, we simulate PREFIRE measured radiances for an overflight of the field site and compare to the observations.
At the surface, simulations of the FINESSE instrument’s output are in very good agreement with observations. Observations from the PREFIRE instrument indicate some persistent biases. In the atmospheric window, a rigorous diagnosis of these biases is impeded somewhat by uncertainty in surface conditions, while instrument noise strongly impacts measurements in the FIR. By quantifying the dominant sources of uncertainty, we highlight proposed techniques for future similar experiments to aid the evaluation of satellite radiances.
How to cite: Pery, B., Brindley, H., Murray, J., L'Ecuyer, T., Michaels, T., Panditharatne, S., Mosselmans, S., and Hogan, R.: Towards ground-to-space spectral radiative closure in the thermal infrared with PREFIRE, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20760, https://doi.org/10.5194/egusphere-egu26-20760, 2026.
