Based on a discovery by Igor Zuykov, Environmental Investigations (EIC) has developed a novel portable subsurface imaging system, termed the RAP PlusTM System, capable of generating detailed images of geological strata layers and underground man-made structures and objects. The system takes advantage of ever-present low-level random vibrations in the ground and detects resonances in these vibrations that naturally occur at the interfaces of strata layers and surface boundaries of structures. These resonances are detected using acoustic sensors in contact with the ground surface. No acoustical or RF signal needs to be injected into the ground, though a light tap on the surface near the sensor may enhance the processing of the received signal. The sensors detect the vibrations and convert them into electrical signals, which are amplified and detected. An algorithm based on the Fourier transform converts the signals from time into frequency domain. Another algorithm is then used to extract the information related to resonances and accurately determine the depth and shape of the strata and structure boundaries. This information is displayed as images in which the layers or structures appear in false colors. A significant advantage of this system that it is immune to electro-magnetic interference and even to strong vibration caused by passing vehicles.
Alexander E. Martens,
"Novel subsurface imaging system", Proc. SPIE 3752, Subsurface Sensors and Applications, (15 October 1999); doi: 10.1117/12.365696; https://doi.org/10.1117/12.365696