We developed a method for directly measuring displacement of a moving surface for use with dynamic or high explosive driven experiments. The technique, called "Modulation Based Ranging" (MBR), overcomes the errors associated with integrating a velocity history of an object undergoing non-radial flow, while also providing the exact displacement of the object with sub 100 µm resolution. A discussion of sources of phase sensitive errors is presented along with a demonstration of the applied corrections. Excellent agreement between MBR and integrated velocity from the Photonic Doppler Velocimetry (PDV) technique was observed when no non-radial flow was present. We then demonstrated the ability of MBR to accurately measure true displacement of a surface subjected to a strong non-radial component.