Stratocumulus properties retrieval method from NOAA-AVHRR data based on the discretization of cloud parameters

A method is presented for determining the optical thickness, effective droplet radius and temperature of oceanic stratocumulus clouds from NOAA-AVHRR infrared channels. The satellite data used in the present study correspond to night-time images in which large-scale stratiform clouds overlay the ocean. The procedure is based on the inversion of an atmospheric radiative transfer model that makes use of the discrete ordinates method called DISORT. A detailed study is presented which shows that cloud parameter retrieval is ambiguous, resulting in several possible solutions, because some pairs of effective particle radius and optical thickness produce the same brightness temperatures. The discretization of these two parameters, based on the cloud layer radiative behaviour, is proposed to avoid these multiple solutions. In addition, the model inversion presents some difficulties that have been solved using a genetic algorithm. The current retrieval scheme is applied to satellite data to compare results with local in situ measurements and a good agreement is obtained in those pixels near the sample site.