title: Retrieval of the optical depth using an all-sky CCD camera.
abstract: A new method is presented for retrieval of the aerosol and cloud optical depth using a CCD camera equipped with a fish-eye lens (all-sky imager system). In a first step, the proposed method retrieves the spectral radiance from sky images acquired by the all-sky imager system using a linear pseudoinverse algorithm. Then, the aerosol or cloud optical depth at 500 nm is obtained as that which minimizes the residuals between the zenith spectral radiance retrieved from the sky images and that estimated by the radiative transfer code. The method is tested under extreme situations including the presence of nonspherical aerosol particles. The comparison of optical depths derived from the all-sky imager with those retrieved with a sunphotometer operated side by side shows differences similar to the nominal error claimed in the aerosol optical depth retrievals from sunphotometer networks.
authors.affiliation: Grupo de Física de la Atmósfera, Centro Andaluz de Medio Ambiente, Universidad de Granada, Junta de Andalucía, Avda. del Mediterráneo s/n, 18071 Granada, Spain. fjolmo@ugr.es
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Olmo
authors.forename: Alberto
authors.initials: A
authors.lastname: Cazorla
authors.forename: Lucas
authors.initials: L
authors.lastname: Alados-Arboledas
authors.forename: Miguel A
authors.initials: MA
authors.lastname: López-Alvarez
authors.forename: Javier
authors.initials: J
authors.lastname: Hernández-Andrés
authors.forename: Javier
authors.initials: J
authors.lastname: Romero