Kansas Geological Survey, Current Research in Earth Sciences, Bulletin 247, part 1
Modeling Dielectric-constant Values of Geologic Materials: An Aid to Ground-penetrating Radar Data Collection and Interpretation--Fig. 5

Fig. 5. Approximate GPR-antenna footprint (Fresnel zone) for bistatic, dipole antennas (adapted from Annan, 1996). This footprint is calculated using Equations (8) and (9). A = long radius; B = short radius; z = elevation, where z(0) is the surface elevation and z(d) is the depth of the Fresnel zone.