The measurement of wave speed is always one of the key problems in the research of subsurface penetraing radar

particularly when the location and image of the targets in the ground are measured.On the basis of the signal features of subsurface penetrating radar

extraction of edge contours which uses zero-crossing points and others traditional methods are discarded.The method of extremum is given for extraction of edge contours.The edge contours of the targets can be extracted more accurately using the method of extremum and the new method generates less data for Hough transform.And according to the analysis of Hough transform and the deficiency of traditional Hough transform

an improved Hough transform is proposed in which a FIR low-pass filter is added to improve the accuracy of Hough transform.The improved Hough transform has better performance than the traditional Hough transform by the evaluation for the practical data.