COMPARISON OF GRADIENT ANALYSIS TECHNIQUES FOR LINEAR TWO-DIMENSIONAL MAGNETIC SOURCES

Six techniques are presented for analyzing magnetic gradient profiles over two-dimensional structures. All use the vertical gradient G//z and most require the computation of the total gradient G equals ROOT G//x**2 plus G//z**2. Four of the methods are mathematically rigorous: one is based on the crossing points of the G//x and G//z profiles; a second, reported by Atchuta Rao et al. , uses G and phi equals arctan (G//x/G//z); and two more are based on the total gradient line-shape. Two other methods, based on the half-slope points of G//z and G, are rule-of-thumb techniques similar to the familiar half-slope method for total field anomalies. These methods have been used to obtain depth estimates from simulated profiles over thick and narrow dikes contaminated by dc offsets, linear trends, and random noise.