AbstractWe present an approach, termed electrochemical tomography (ECT), for the in-situ study of corrosion phenomena in general, and for the quantification of the instantaneous rate of localized corrosion in particular. Traditional electrochemical techniques have limited accuracy in determining the corrosion rate when applied to localized corrosion, especially for metals embedded in opaque, porous media. One major limitation is the generally unknown anodic surface area. ECT overcomes these limitations by combining a numerical forward model, describing the electrical potential field in the porous medium, with electrochemical measurements taken at the surface, and using a stochastic inverse method to determine the corrosion rate, and the location and size of the anodic site. Additionally, ECT yields insight into parameters such as the exchange current densities, and it enables the quantification of the uncertainty of the obtained solution. We illustrate the application of ECT for the example of localized corrosion of steel in concrete.