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Radar Image Processing for Locating Underground Linear Objects

This paper presents an image processing method for locating underground linear objects using ground-probing radar data. One of the problems when using groundprobing radars is how to know the microwave propagation velocity in the ground of the test area. The proposed method employs the Hough transform of the edge contours of pulse echoes in a radar image, which appear as hyperbolas, whose shape contains the velocity information. 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 horizontal location of the object and the square of velocity as its two axes to rapidly estimate the velocity. The second one, which transforms each edge position to a parabola on the transform plane having the horizontal location of the object and the square of echo response time as its two axes, realizes aperture synthesis to give a focused echo source. A preliminary experiment confirms accurate depth measurement for multiple parallel pipes lying close toghether.