Abstract: A methodology is applied to reconstruct vertical pro?les of the absorption (a) and scattering (b) coeffcients in natural waters from in situ radiance measurements in several depths and single wavelength. A multi-region (R=10) approach is employed and these coeffcients are assumed as being constant in each region. The inverse problem is iteratively solved using the radiative transfer equation as direct model. Bio-optical models are employed to correlate the chlorophyll concentration to the coeffcients a and b. At every iteration, the inverse solver generates a candidate solution that is a set of discrete chlorophyll concentration values for each region. The radiative transfer equation is solved using these values by the Laplace transform discrete ordinate (LTSn) method for polar and azimuthal scattering angles. An objective function is given by the square di?erence between reconstructed and experimental radiances at every iteration. In order to compensate the nearly exponential radiance decay with depth, that unbalances the in?uence of radiances of different depths, a depth correction factor is used to adjust radiance values at each level. The referred objective function is minimized by an Ant Colony System (ACS) implementation. A new regularization scheme pre-selects candidate solutions based on their smoothness, in addition to the classical Tikhonov regularization. Another chlorophyll candidate pro?le is generated and iterations proceed. Synthetic and real data show the suitability of the proposed method.