Importance of Direct Vertical and Horizontal Magnetic Gradient Measurements in Detecting Subsurface Engineering Targets: A Case Study in Central Iraq

This study is carried out to investigate the role of direct measurements of vertical and horizontal magnetic gradient to detect the subsurface an engineering utilities, including electrical cable and concrete irrigation canal at a site the University of Baghdad campus, southern Baghdad, central Iraq. The measurement was achieved along three E-W parallel profiles. The length of each profile is 14 m. The spacing distance between each two adjacent profiles is 1 m, whereas the station spacing distance along each profile is 1 m. The vertical and horizontal magnetic gradient in the surveys were achieved by using two sensor levels, at 2.44 m and 1.0 m, respectively. The total magnetic intensity, vertical gradient, and horizontal gradient were measured, then an analytical signal was determined. The location of the electrical cable appears as a positive peak within the total magnetic intensity and vertical gradients curves, while the concrete canal location is shown by a negative peak in all profiles. On the other hand, the horizontal magnetic gradient curves revealed the location of the electrical cable as a negative peak, while the concert boundaries appeared as positive peaks. The analytical signal shows that the electrical cable gives a positive peak, while the concrete canal boundaries a negative peak. It is concluded that the vertical magnetic gradient is very similar in shape with the total magnetic intensity measurements of low sensor level (1 m). The vertical gradient, on the other hand, shows the best result for investigating the target in the study area, with depth not exceeding 2 m.