  This paper is concerned with the numerical solution to a 3D coefficient
inverse problem for buried objects with multi-frequency experimental data. The
measured data, which are associated with a single direction of an incident
plane wave, are backscatter data for targets buried in a sandbox. These raw
scattering data were collected using a microwave scattering facility at the
University of North Carolina at Charlotte. We develop a data preprocessing
procedure and exploit a newly developed globally convergent inversion method
for solving the inverse problem with these preprocessed data. It is shown that
dielectric constants of the buried targets as well as their locations are
reconstructed with a very good accuracy. We also prove a new analytical result
which rigorously justifies an important step of the so-called "data
propagation" procedure.
