Fig. 1

Phase velocities obtained from an array with a radius of r = 0.58 m. The thick yellow line represents average values and the thin yellow lines show the standard deviations. A reference model (thick solid line) constructed based on arrays with radii from 5.8 m to 555 m (see the later section) is also plotted for reference. The four straight lines from the origin represent constant wavelengths of 50r, 100r, 200r, and 300r (the straight lines from the origin represent constant wavelengths; (phase velocity) = (wavelength) \(\times\) (frequency)). The lowest limit of the analyzable frequency range (indicated by the arrow) corresponds to a wavelength of 269r