An aim of the EarthCARE mission is to perform radiative closure assessments of cloud and aerosol properties, inferred using measurements from the EarthCARE instruments. This assessment is performed by comparing measured and modelled outgoing radiative energy emitted by Earth (thermal) as well as sunlight reflected by Earth (solar) with agreement being related to the accuracy of cloud and aerosol properties. This assessment is important as EarthCARE cloud, aerosol and radiation measurements are combined to understand processes that will be used to improve models of weather and climate, as well as understand changes, including Earth’s energy budget.

Radiative energy measurements are made using the Broadband Radiometer (BBR) on EarthCARE. The BBR infers outgoing top-of-atmosphere radiative fluxes (radiative energy in all directions) over a wide range of wavelengths using measurements of radiance (radiative energy in a narrow cone in a particular direction) in three views along the satellite track (forward, backward and straight down or nadir). Modelled radiances and fluxes are produced using 3D radiative transfer models applied to profiles of aerosols and clouds from EarthCARE.

This Image of the Month demonstrates measured and modelled solar fluxes and radiances. The upper plot shows measured (black) and modelled (red) fluxes for a section of an EarthCARE orbit over the Indian Ocean (frame 03600E, 15 January 2025). Each point is a mean value averaged over a 5 x 21 km area. The lower plot shows the radiances in the nadir direction. The measured and modelled values mostly agree well, suggesting that, for this stretch, the retrieved cloud and aerosol properties are accurate.

The two images show a scene spanning from dark ocean to thick bright clouds. The upper of the two images shows nadir radiances from the Level 1 BBR single pixel product (BBR_SNG_1B) for the highlighted part of the above plots. The lower image shows the corresponding values produced by the 3D radiative transfer model that operates on retrieved cloud and aerosol properties from the Level 2b ACM-CAP product (ACM_CAP_2B). Again, these images agree well, especially between +/-3 km across track. This shows that it is possible to use EarthCARE for radiative closure assessments, including extension to the pixel level, and it is performing well. This supports the objective of the EarthCARE mission to make global observations of clouds, aerosols and radiation.