The depth of a caesium-137 radioactive source buried in sand has been determined using Principal Component Analysis. A bespoke phantom filled with fine-grade silica sand has been used. The source was placed in the sand at depths of between 5 to 50mm, using a calibrated source slider. At each depth, γ-ray spectra were recorded at an external face of the phantom using a cadmium telluride γ-ray detector. A model was then developed relating the depth to the output of the Principle Component Analysis. Two principal component vectors have been extracted for each depth spectrum. The angle (θ) between these at each depth is used to derive a function of depth.