Advantages of Electromagnetic Interferometry Applied to Ground-Penetrating Radar : Non-Destructive Inspection and Characterization of the Subsurface Without Transmitting Anything

Ground-penetrating radar (GPR) is a non-destructive method that images the subsurface using radar. A transmitter generates a radar pulse. This signal propagates into the ground where it reflects against subsurface heterogeneities, and travels back to the surface. A receiver records the reflected signal. The reflected signal contains information about the subsurface. GPR is useful for pavement- and structures- inspection, object-detection, and characterization of the subsurface. For example, many forms of pavement damage of highways originate in the bottom layers and are invisible until the pavement cracks come to surface. GPR can indicate pavement damage before it is visible at the surface, so that preventive actions can be performed where necessary. We work towards developing GPR without the need to transmit any signal. Instead, we use signals that are already available in the air, such as mobile phone signals. A technique called electromagnetic interferometry selects those signals that are measured before they enter the ground and after they reflect. It extracts the path from receiver to subsurface and back to the receiver. The result looks as if the receiver has transmitted a signal, while no signal was transmitted by that receiver. This receiver is called a virtual source. By repeating this step for many receiver combinations we create a virtual dataset. This virtual data provides a well-interpretable image of the subsurface.