  The local density of states (LDOS) and its Fourier component induced by a
unitary impurity in a supercurrent-carrying d-wave superconductor are
investigated. Both of these quantities possess a reflection symmetry about the
line passing through the impurity site and along the supercurrent if it is
applied along the antinodal or nodal direction. With increasing supercurrent,
both the coherence and resonant peaks in the LDOS are suppressed and slightly
broadened. Under a supercurrent along the antinodal direction, the coherence
peaks split into double peaks. The modulation wavevectors associated with
elastic scatterings of quasiparticles by the defect from one constant-energy
piece of the Fermi surface to another are displayed as bright or dark spots in
the Fourier space of the LDOS image, and they may be suppressed or enhanced,
and shifted depending on the applied current and the bias voltage.
