A commercial all-sky-camera is employed to derive a whole-sky product of Cloud Optical Depth. The methodology consists in a radiative closure combining measurements of the blue and red channels with libRadtran 1D monochromatic radiance simulations. Besides, a matrix of data quality Flags is obtained for every COD image. The data quality Flags indicate the reliability of the retrieval at each pixel, and gives information about the method to solve the radiance monochromatic ambivalence. In addition, the Flags product also indicates the presence of out-of-range radiances with respect to the RT simulations. Such out-of-range radiances are related to the neglection of horizontal radiation transport in the 1D plane-parallel approach. A set of around 2000 images during 2020 have been analyzed and COD has been obtained for each pixel. The COD shows values ranging from 0 to 130, with around 83% of the cases between 5 and 30. Our COD results have been validated using the zenith COD retrieval from AERONET. Our results present a very good agreement with AERONET cloud mode retrieval and show a correlation factor of 0.94 and a slope of 0.99 respectively.

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Caterina Peris-Ferrús, José Luís Gómez-Amo, Pedro C. Valdelomar, Francesco Scarlatti, Roberto Román, Claudia Emde, and Maria Pilar Utrillas, "Retrieval of cloud optical depth: synergies between whole sky imagers and radiative transfer modeling.," Proc. SPIE 11859, Remote Sensing of Clouds and the Atmosphere XXVI, 118590W (Presented at SPIE Remote Sensing: 12 September 2021; Published: 12 September 2021); https://doi.org/10.1117/12.2599586.