FIG. 4. Inverse model for soil properties (IMSP) inversion history for a known standoff. The relative uncertainty is 10% (RDP is the relative dielectric permittivity). Triangles are initial models, squares are acceptable solutions, and circles represent the logarithm of the residual at each iteration. Initial models on the left side of the figure descend to acceptable solutions, while those on the right descend to a local minimum that does not meet the stopping criterion (Eq. [4]).