Dictionary:Fig D-15

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FIG. D-15. Directivity graphs. (a) Polar plot showing the relative amplitude of a radiated wave (or the relative sensitivity to waves approaching a geophone array from different directions). The horizontal axis can be expressed in various ways. (b) Directivity of five inline geophones spaced 10 m apart. (c) Response of a tapered array of five geophones spaced 20 m apart and weighted 1:2:3:2:1; such weighting could be achieved with nine geophones distributed as the weighting. (d) Response of nine geophones equally spaced 5.5 m apart. The solid curves are for harmonic (steady-state) waves, the dashed curves for a transient with a bell-shaped spectrum peaked at 30 Hz and a width of 30 Hz. (From Sheriff and Geldart, 1995, 249.)