An investigation of large-scale boundary-layer structures using optical wavefront sensing techniques is described. Measurements were conducted in Notre Dame’s Tri-Sonic facility at M = 0.4 and 0.5 with a range of sampling frequencies and spatial resolutions as well as the Merill Wind Tunnel facility at Caltech at M = 0.03. In this paper we present several techniques for determining optical wavefront energy spectra and the implications of those techniques to large-scale structures. Finally we investigate the effect of Reynolds number on the wavefront spectra in a turbulent boundary-layer. The data has shown an increase in Reynolds number causes a significant energy shift toward lower $St_\delta$, indicating that optically active large scale structures grow larger with increase in Reynolds number.