Reconstruction of Chlorophyll Concentration Profile in Offshore Ocean Water using a Parallel Ant Colony Code

An inverse hydrologic optics problem is solved using a recent intrinsic regularization scheme coupled to a standard Ant Colony System (ACS). The regularization scheme pre-selects candidate solutions based on their smoothness, quantified by a Tikhonov norm. The Chlorophyll profile is reconstructed from radiance experimental measurements in the ocean water for several depths and single wavelength. Vertical profiles of the absorption and scattering coefficients are estimated from the Chlorophyll profile by means of bio-optical models. The inverse problem is formulated as an optimization problem and iteratively solved by an ACS using the radiative transfer equation as direct model. An objective function is given by the square difference between computed and experimental radiances at every iteration. Each candidate solution corresponds to a discrete Chlorophyll profile. The radiative transfer equation is solved using the Laplace transform discrete ordinate (LTSN) method. A parallel implementation of the Ant Colony System is used and executed in a distributed memory machine. Test results show the suitability of the proposed method.