A method and apparatus for processing images, the method comprising: using a radar (4), generating a first image of an area of terrain (8); using a sensor (5), generating a second image of the area of terrain (8); performing an image segmentation process on the first image to identify a point in the first image as corresponding to a ground surface of the area of terrain (8); and projecting the identified point in the first image from the first image into the second image to identify a point in the second image as corresponding to the ground surface of the area of terrain (8). The method may further comprise: for the identified point in the second image, defining a sub-image of the second image containing that point; and performing a feature extraction process on the sub-image to identify points in the sub-image that correspond to the ground surface