A simple and accurate means of predicting the locus of constant travel time of an underground scatterer for air-launched bistatic GPR

GPR imaging often uses contours of constant wave travel time or electrical path length to determine possible locations of buried targets. The intersection points of two contours triangulates the target. If the GPR is above the ground, rays from the source refract at the ground interface as they enter the ground, and as such yield non-intuitive loci of constant travel time. A simple method is presented to determine these loci as a continuous and smoothly connected piecewise combination of conic sections. These loci are compared with FDFD generated contours with good agreement.