A phantom has been used to position two radiation sources, separately, when buried under dry-silica sand at depths between 5 and 50 mm. A γ-ray energy spectrum was then measured at every 1 mm depth. Principal component analysis has been conducted, which has led to anon-linear fit being established, allowing the depth of entrainment to be accurately inferred. The technique has been expanded for additional shielding media: water, aggregate and both wet and dry soil. The technique has also been expanded beyond the previous depth constraint of 50 mm.