f Ground penetrating radar ability to detect leaks from water pipe

The problem of detection of leaks from water pipe without digging the pipe out is of constant interest to city services. To solve this problems many different geophysical methods can be used: radiolocation, seismics, resistivity imaging etc. This paper describes numerical modeling of ground penetrating radar detection of metal pipe with a leak buried in sandy soil with various levels of water content. Relative dielectric permittivity was 5 to 30 dependent on water content. Complex dielectric permittivity was an approximation of results obtained in [1] in modeled GPR frequency range. Spatial distribution of soil water content around the leak area was considered stationary and based on the work [2]. The leak was supposed to be a linear water source along the pipe. Boundaries of areas with given value of water content were non-coaxial elliptical cylinders with their axes displaced down relative to pipe axis. The ground around the pipe in case of the leak had maximum possible water content (30%). Monostatic pulse ground penetrating radar survey was modeled by calculating signals reflected from the pipe and from subsurface dielectric inhomogeneity due to the leak. The polarization of electric field was along the pipe axis. Transmitted signal was a real GPR signal with 4 half-periods, each with duration about 4 ns. Transition coefficient conditioned by subsurface reflections was calculated in frequency domain. Then time domain signals on the receiver were found. Calculations were carried out for metal pipes of various diameter buried at depths 2-3 m, mean water content of the ground being 5%-15%. GPR survey data were simulated by adding the direct signal between transmitter and receiver and calculating received signals in points along the line perpendicular to the pipe at 20 cm steps, starting over the pipe.