The simulation of transmitter-reciever-transmitter (TRT) configured ground-penetrating radars over heterogeneous grounds was discussed. The finite-difference time-domain (FDTD) methods along with the perfectly-matched layer (PML) absorbing boundary conditions (ABC) were used for the simulations. Scattered-field image demonstrated that the buried target was easily detected when buried in a homogenous ground. Results show that the TRT-configured GPR is sensitive to surface roughness and the main source of noise is the detoriorations in the ground-air interface.