Abstract: Method for discriminating defects present on a frontside of a transparent substrate from defects present on a backside of the substrate comprises disposing the substrate in an inspection system in which first and a second light beams intersect at a measurement spot on the frontside of the substrate. Relative movement of the substrate and measurement spot is controlled such that a reference plane is kept tangential to the measurement path. A first pattern is identified in a measurement signal, the first pattern corresponding to light scattered by a particle on the backside of the substrate and presenting two intensity peaks separated from each other by a determined separation interval corresponding to the time necessary for the defect to be moved over the distance separating two illumination spots on the backside of the substrate.