It is possible to select the hydrophone component, the vertical component (Z) or the horizontal component (X). For a given component, the figure on the left shows a seismic section (time-distance), the figure on the right shows the 2D amplitude spectrum. On the time-distance section, whatever the selected component, the underwater guided waves are very energetic. Data having been corrected by a 1520 m/s apparent velocity, time t=0 corresponds to the arrival time of the direct wave. We observe refracted arrivals that are preceding guided waves and a reflected deep arrival that goes through the section.

In f-k space, only the guided waves are clearly visible. A velocity correction (V_g= 1520 m/s) has been applied to bring back initial data in a reduced distance in wavenumber domain. In the f-k space, we observe several guided modes clearly separated respectively in the frequency range [0-80 Hz] and in the wavenumber range [0-5 km^-1]. To a given frequency is associated a discreet number of wave numbers which correspond to modes associated to this frequency.

The 3 first modes can be selected in f-k space by filter with masks. These modes are shown on the figure on the left in x-t domain and on the right in f-k domain. Each mode corresponds a dominant frequency, which increases with the mode order. In x-t domain, each mode is represented by a simple image, whereas the sum of the modes (initial data) is a complex image.