ADM-Aeolus retrieval algorithms for aerosol and cloud products

Abstract

ADM-Aeolus, the wind Lidar under development at ESA, is a High Spectral Resolution Lidar that additionally provides separated information on particles (Mie channel) and molecules (Rayleigh channel). Lidar signals will be accumulated in vertical range bins in order to reach sufficient signal-to-noise ratio for reliable wind estimates. The vertical range bin integration may vary from 250 m near the surface up to 2 km in the upper troposphere and lower stratosphere. Significant attenuation in a range bin changes the nature of the retrieval problem. The commonly used Lidar inversion techniques appear to be inadequate to process bin-accumulated signals. This paper presents the 'L2A processor', conceived to use ADM-Aeolus signals to provide information on aerosol and cloud layers optical properties. The altitude, geometrical depth, optical depth, backscatter-to-extinction ratio and scattering ratio are to be retrieved. The L2A processor algorithms provide a new formulation to the inverse problem for various filling cases of a range bin and it includes a credibility criterion (CC) in order to select the best filling approximation. The effective vertical resolution can be two to four times better than the ADM-Aeolus range bins. The basic concept, the processing algorithms, numerical examples and sensitivity tests are here presented.