Algorithm Theoretical Basis Document (ATBD) for A-FeatureMask (ATLAS)

The atbd describes the Featuremask algorithm for the ATLID lidar signals onboard the EarthCARE satellite.
This algorithm generates a feature mask based on the correlation present in the data itself without critically relying on a-priori input thresholds. At the single-shot scale the signal strength associated with aerosol or very optically thin ice clouds can be comparable to the noise levels, therefore it was chosen to rely on image reconstruction techniques and not on a-priori signal to noise ratios and thresholds. The main reason why an image reconstruction technique can be so effective for the ATLID data is that, in principle, the Mie signals contain only particle backscatter and noise due to the Mie-Rayleigh cross-talk. No molecular backscatter, e.g. no variable background signal, should be present in these channels.