RADAR IMAGE-PROCESSING FOR LOCATING UNDERGROUND LINEAR OBJECTS

This paper presents an image processing method using ground-probing radar data taken by synthetic aperture radar. The method locates underground linear objects such as pipes carrying telephone/electricity cables, and it realizes high measurement accuracy with short computation time. One of the problems when using ground-probing radars is how to know the microwave propagation velocity in the ground of the test area. The proposed method employs the Hough transform of segmented edge contours of pulse echoes in a radar image, which appear as hyperbolas conveying the velocity information in their shapes. The method uses two types of Hough transformation. The first one transforms each edge position and orientation to a straight line on the transform plane that has the antenna location and the square of velocity as its two axes. This transform realizes rough estimation of the velocity in a very short time. The second one, which, for a given velocity, transforms each edge position to a parabola on the transform plane having the horizontal locations of echo source and the square of echo time as its two axes. This transform duplicates the aperture synthesis process to give a focused echo source. By repeating the second transform with various velocities around an initially estimated value, the final velocity and object locations are obtained. A preliminary experiment confirms accurate depth measurement for isolated pipes and for multiple parallel pipes lying close together.