An estimation method of buried pipe location by using zero-crossed synthetic aperture

Abstract

In the buried-object search technique using a pulsed radar, the estimation method for the buried-pipe location and the underground propagation velocity of the electromagnetic wave by means of a synthetic aperture method has been studied. In general, the electromagnetic wave attenuates as it propagates in the underground and the amplitude of the received signal often becomes extremely small. Therefore, it has been difficult in the signal processing using the amplitude value to recognize several buried objects at different depths by an identical discrimination standard. To resolve this difficulty, a new zero-crossed synthetic aperture method is developed. In the underground cross-sectional image, the waves reflected from a buried pipe form a hyperbolic pattern dependent on the underground propagation velocity of the electromagnetic wave. By evaluating only the edge of this hyperbolic pattern, the underground propagation velocity of the electromagnetic wave and the location of the buried object are estimated. First, to extract the edge, the amplitude value at the time when the observed signal has a “0” amplitude is replaced with “1” if the phase of the original waveform changes from minus to plus whereas with “-1” if it changes from plus to minus. The amplitude at other time points is replaced with “0.” Subsequently, a synthetic aperture process (addition process) is carried out. Since the absolute value of the amplitude is 1 or 0, it is not necessary to consider the effect of the attenuation of the amplitude due to propagation of the electromagnetic wave as a discrimination reference in the estimation of the location of the buried pipe after the addition process. The location of the buried pipe can be detected accurately.