Evaluation of EarthCARE’s Scene Construction Algorithm Using Airborne Observations

Abstract. This study evaluates the performance of EarthCARE’s scene construction algorithm (SCA) using airborne observations collected by the National Research Council Canada’s Convair-580 research aircraft during the EarthCARE Commissioning Calibration/Validation Campaign in Ottawa (ECALOT). EarthCARE’s three-dimensional (3D) SCA employs a radiance-matching technique and nadir retrievals to construct 3D atmosphere-surface conditions around the nadir cross-section. While the SCA can be applied across the ~150 km swath of EarthCARE’s Multispectral Imager (MSI), its operational application is limited to a ~30 km-wide region centered on the nadir track., which encompasses the 5 km across-track by 21 km along-track assessment domains and their associated buffer regions. The SCA facilitates lateral transport of photons in Monte Carlo radiative transfer simulations, and so its results influence simulated radiative quantities that are used, in part, to perform radiative closure analyses. Two complementary evaluation strategies are applied. First, the Convair-580 underflew EarthCARE on a path angled at 20° to the satellite’s track. Off-nadir measurements of cloud microphysical variables made in situ by the Convair-580 are used to assess SCA predictions for shallow cumulus and stratocumulus clouds. Second, for nimbostratus clouds, the Convair-580’s side-viewing W-band radar reflectivities are compared to horizontal planes of reflectivities based on SCA allocations of nadir reflectivities from both Convair-580 and EarthCARE’s Cloud Profiling Radar. Evaluation against in situ observations showed little variation in mean bias error (MBE) and root mean square error (RMSE) for both liquid water content and effective radius at distances of up to ~12 km from the nadir track, indicating consistent SCA performance within this range. Comparison with side-viewing W-band radar reflectivity also yielded low MBE and RMSE, with correlation coefficients of 0.88 and 0.80 for Flights 6 and 5, respectively. The newer version of the SCA, Baseline BC, generally outperformed the earlier Baseline BA, particularly for the more complex cloud scene observed during Flight 5 on January 27, 2024.