New developments on reconstruction of high resolution chlorophyll-a vertical profiles

Roberto P. Souto, Pedro L. Silva Dias, Haroldo F. Campos Velho, S. Stephany, M. Kampel


We present a methodology to reconstruct vertical profiles of chlorophyll-a pigment concentration in open-ocean waters based on radiance values at different depths. The inverse problem is formulated here as an optimization problem and iteratively solved by an Ant Colony System (ACS) meta-heuristic. An objective function is given by the square difference between computed and experimental radiances at each iteration. The Laplace transform discrete ordi- nate (LTSN) method is used to solve the radiative transfer equation (direct problem) in order to compute the radiances. In a first approach, this methodology was not able to reconstruct profiles with two or more peaks of chlorophyll-a concentration. This result can be partially explained by the relatively low number of sampling points (11 points), that limits the geometric resolution of the vertical profile to be reconstructed. Alternatively, we propose the reconstruction vertical profile using a higher geometric resolution, lower than one meter, in order to evaluate the ability of identifying any peak in chlorophyll-a concentration. A hybrid methodology is adopted: ini- tially, the original inverse ACS methodology is employed to retrieve a high resolution profile (81 points), and then this result is used as an initial guess for the deterministic method of optimiza- tion Levenberg-Marquardt to refine the profile.


radiative transfer equation, ant colony system, Levenberg-Marquardt, hydrologic optics, chlorophyll-a profile

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