The positioning of buried pipelines from magnetic data

Abstract

Buried pipelines are “lifelines” for cities; therefore, it is vital to understand their location and depth before municipal construction to prevent them from being damaged. Magnetic methods have been applied to detect buried ferrous metal pipelines such as steel and cast-iron pipes. We have developed a positioning method for buried pipelines from magnetic data, which is based on a combination of the tilt angle and the downward continuation. The magnetic tilt angle can provide information about the location and depth of buried pipelines, which can easily be calculated by the horizontal and vertical magnetic field gradients. We prove that the tilt angle for the magnetic field that has been reduced to the pole is independent of the magnetization direction given by the pipeline direction with respect to the inducing field. A tilt angle of 90° marks the location of a buried pipeline, whereas the depth is the distance between the location of the 90° and its adjacent 0°. The iterative Tikhonov regularization method for downward continuation, while separating the superimposed anomalies and enhancing the horizontal resolution, also reduces the influence of fast Fourier transform-induced noise and other noise that is intrinsic to the data set. We use the derivative of the Tikhonov regularization result as a regularization term of the minimization function and a constraint for the regularization parameter choice to obtain a more stable and accurate downward-continued result. This positioning method is applicable to single and parallel pipeline detection.