Radiative Closure Assessment of Retrieved Cloud and Aerosol Properties for the EarthCARE Mission: The ACMB-DF Product

Measurements made by three instruments aboard the EarthCARE satellite, plus data from auxiliary sources, will be used to synergistically retrieve estimates of cloud and aerosol properties. The ACMB-DF processor consists of a continuous radiative closure assessment of these retrievals and is both described and demonstrated in this study. The closure procedure begins with 3D radiative transfer models (RTMs) acting on retrieved and auxiliary data. These models yield upwelling shortwave and longwave broadband radiances commensurate with measurements made by EarthCARE’s multi-angle broadband radiometer (BBR). Measured and modelled radiances are averaged up to “assessment domains”, that measure ~21 km along-track by no more than 5 km across-track, centred on the retrieved cross-section of ~1 km profiles, and are then combined, by angular distributions models (ADMs), to produce “effective” upwelling fluxes at the top-of-atmosphere, denoted as FBBR and FRTM, respectively. Last, the probability 𝑝ΔF^ of |FRTM – FBBR| being less than ΔF^ W m-2 is estimated recognizing as many sources of, assumed normally distributed, uncertainties as possible. For historical/programmatic reasons, ΔF^ is set to 10 W m-2, but that might change during EarthCARE’s commissioning phase and with Sun angle. The closure process is demonstrated up to calculation of 𝑝ΔF^ using four 400 km-long portions of one of EarthCARE’s test frames for which simulated passive measurements were computed by 3D RTMs. Note that this study, like the ACMB-DF process with real EarthCARE observations, does not comment explicitly on performance of retrieval algorithms.