This paper presents a new method to remove the effects of uneven ensonification in Side-Scan Sonar (SSS) acoustic images, facilitating their use in underwater robotics. A Lambertian model is used for the sonar scattering process, relating the received echo with the ensonification intensity, the sea bed reflectivity and the incidence angle. As for the ensonification intensity, a sensitivity pattern model is adapted to SSS sensors. By means of these models, SSS imagery  is significantly improved.