Abstract: An implicit inverse method is used to determine eddy diffusivity. The inverse problem takes the form of an optimizatiom problem: minimizing a functional composed with one term that measures the distance between experimental and computed data and a regularization term that imposes to the solution a certain-degree of smoothness. The purpose of this paper is to analyse different regularization functionals. Six regularization methods are tested: zeroth-order, first-order and second-order Tikhonov regularization, and zeroth-order, first-order and second-order entropic regularization.