1. A system for detecting and locating changes in an underground region, comprising: a mobile ground penetrating radar (GPR) system having a linear array of antenna elements each configured to transmit a radar signal into an underground region and to receive a return radar signal from the underground region, an electromagnetic field generated by each antenna element during transmission being substantially the same as an electromagnetic field generated by each of the other antenna elements during transmission and an antenna receive pattern of each antenna element during reception being substantially the same as an antenna receive pattern of each of the other antenna elements during reception; a radar processor in communication with the GPR system and configured to generate a GPR image of an underground region; and a registration module in communication with the radar processor and configured to determine a lateral offset of the linear array between a pass over the underground region at a first time and a pass over the underground region at a second time, the registration module configured to spatially align a GPR image acquired for the first time and a GPR image acquired for the second time, and to generate a GPR difference image based on the spatially aligned GPR images, wherein the GPR difference image includes data representative of changes to the underground region that occur between the first and second times.