SEOM CIRCAS

CIRCAS aims at providing a set of atmospheric (cloud and aerosol) and surface (albedo) products derived from S3A/SLSTR observations retrieved using the same radiative transfer physics and assumptions.

The retrieval is based on the CISAR (Combined Inversion of Surface and Atmosphere pRoperties) algorithm. CISAR is an advanced mathematical method developed by Rayference for the joint retrieval of surface reflectance and atmospheric (cloud and aerosols) properties from observations acquired by space-based imagers.

The CISAR algorithm relies on the FASTRE radiative transfer model that describes surface reflectance and atmospheric absorption/scattering processes. The lowest level represents the surface. The lower layer hosts the aerosols. Molecular scattering and absorption are also taking place in that layer which is radiatively coupled with the surface for both the single and the multiple scattering. The upper layer is only subject to molecular absorption.

The inversion of the FASTRE model within the CISAR algorithm against satellite observations provides accurate estimates of the surface reflectance field, aerosol or cloud optical thickness and single scattering properties in each processed spectral band. An estimate of the retrieval uncertainty is also provided.

As the proposed method retrieved both cloud and aerosol properties with the same retrieval algorithm, no cloud mask is needed to perform the retrieval. Additionally, the same algorithm can be applied over any type of surfaces, including dark or bright surfaces or water bodies.