A potential FeatureMask algorithm for the EarthCARE lidar

The Earth Clouds, Aerosol and Radiation Explorer (EarthCARE) is a combined ESA/JAXA mission to be flown in 2013. EarthCARE will study the spatial distribution of clouds and aerosols and their effects on radiation by combining active (Doppler radar, HSRL lidar) and passive sensors (multispectral imager, broadband radiometer).
In this work a potential feature mask detection algorithm for the EarthCARE lidar is described, where the feature mask identifies 'significant return' in the lidar signal. As the signal strength of aerosol or very optically thin ice clouds on the single shot grid can be comparable to the noise levels it was chosen to rely on image reconstruction techniques and not on signal to noise ratios and thresholds. The main reason why an image reconstruction technique can be so effective is that in principle the lidar Mie signals contain only particle backscatter, background noise and noise due to the Mie-Rayleigh cross-talk. This type of algorithm ensures the derivation of a feature mask on the single shot resolution enabling both the use of variable masks, e.g. use only those profiles which are sure to have no clouds to derive the mean aerosol signals, and calculation of feature fractions which can result in a better determination of higher order products like extinction, backscatter and depolarization.
The algorithm and results for a number of different model scenes including ice clouds, liquid clouds and aerosol layers, as well as real Calipso scenes will be presented