The application of non-intrusive experimental techniques is a break-through in the comprehension of the physical mechanisms governing roughness-induced transition in hypersonic flows. In this thesis, IR Thermography, Planar and Tomographic Particle Image Velocimetry are applied. They show a great potentiality in quantifying the most relevant flow features upstream and downstream of three-dimensional roughness elements. Particularly, non-intrusive measurements of the two-dimensional and three-dimensional velocity flow fields are reported and discussed.