Linear wave theory was first presented by Airy (1845) to provide methods to calculate wave characteristics such as height, period, and speed using a sinusoidal model of the waveform. Based on the ratio of water depth, h, to deep-water wavelength L_o, three different wave regions can be identified: deep water (h/L_o>0.5), intermediate water (0.5>h/L_o>0.05), and shallow water (h/L_o<0.05). This is exceptionally well explained by Masselink in J. Holden, ed. (2012). Linear wave theory relies on the assumption of closed circular particle orbits, but this assumption breaks down in the transition zone approaching shore, where waveform changes occur.