The estimation of buried pipe diameters using ground penetrating radar

Abstract

The generalised Hough transform method is applied to the
\nmeasurement of the diameters of buried cylindrical pipes by
\nGround Penetration Radar (GPR). 600 MHz radar scans
\nacross long pipes, buried in one metre or so of soil, show
\ncomplex reflection patterns consisting of a series of inverted
\nhyperbolic arcs.
\nThe time of flight t(y) as the probe is scanned along
\nan axis, y, perpendicular to the pipe, shows an arc whose
\nshape depends on four unknown variables: y0, the position
\nof the centre of the pipe along the scan, z0, the depth of the
\npipe centre, R, its radius and V the velocity in the medium.
\nAnalytic expressions for the solution of these variables have
\nbeen obtained. They use sets of between 1 and 4 times ti at
\ncorresponding positions yi, along the arc, depending on the
\nnumber of variables to be determined. In the generalised
\nHough method many such sets of times are chosen randomly
\nfrom points on the arcs. The results are presented for example
\nas peaks in an accumulator space for each variable.
\nThe method is demonstrated for a 0.18 m radius concrete
\npipe buried at a nominal 1 m depth in a road. Using data
\nacquired at 600 MHz frequency (around 0.16 m wavelength
\nin soil) the estimated radius was 0.174 ± 0.059 m.