  Motivated by the recent scanning tunneling microscopy (STM) experiment [J. E.
Hoffman, {\it et al.}, Science {\bf 297}, 1148 (2002)], we investigate the
energy-dependent modulation induced by a weak and extended defect in a d-wave
superconductor. The Fourier component of the local density of states (LDOS) is
calculated up to the first order in the defect parameters. Our numerically
obtained image maps together with the energy-dependent charge modulation wave
vectors at different dopings exhibit the essential features as those measured
by the experiment. We also predict new modulation wave vectors in the first
Brillouin zone. Hopefully, they could be verified by future STM experiments.
