Abstract: An important topic in radiative process is the estimation of some characteristcs of the media and/or other conditions of the problem. This estimation process can be formulated as an inverse problem. The source term and some optical material properties have been obtained using a formulation in which the inverse problem is solved as an optimization problem. This work presents an estimation of boundary conditions for natural waters, where the forward problem is solved by LTSn method. The reconstruction is made using radiance or irradiance, where two approaches are used: parameter and function estimation. The expansion coefficients are determinated for the former method, while the function sampled is found in latter approach. The method was tested with data corrupted with Gaussian noise, where the Thikhonov regularization was used.