A pre-regularization scheme for the reconstruction of a spatial dependent scattering albedo using a hybrid ant colony optimization implementation

This work presents a regularization technique applied to an inverse radiative transfer problem formulated as a finite dimensional optimization problem and solved by a hybridization of the ant colony optimization (ACO) with the Levenberg–Marquardt method. It is considered a one-dimensional isotropically-scattering medium with finite optical thickness, space dependent scattering albedo and plane-parallel geometry. The direct radiative transfer problem models transmission of radiation through this medium by the linear version of the Boltzmann equation considering polar angle discretization and azimuthal symmetry. A discrete ordinates method combined with the finite difference method is employed to solve it. Reconstruction of the albedo profile is performed from the intensities of the polar-discretized emergent radiation acquired with external detectors, using a recently proposed regularization technique. Since smooth albedo profiles are expected, such information is used in a new generation of ants in order to perform a pre-selection of the ants. This scheme can be viewed as a kind of pre-regularization in face of the reconstructed profiles that are smooth and show good agreement with the exact solution. In addition, this scheme saves processing time as fewer candidate solutions (ants) are evaluated. Noiseless and noisy data of the emergent radiation intensities were employed in the reconstructions.