Apparatus and method for detecting an underground structure

Abstract

An apparatus and method for locating an underground object or structure by employment of a radar-like probe and detection technique is disclosed. The underground structure is provided with a device which generates a specific signature signal in response to a probe signal transmitted from above the ground. Cooperative action between the probe signal transmitter at ground level and the signature signal generating device provided on the underground object provides for accurate detection of the subsurface object, despite the presence of a large background noise signal. The depth and, if desired, orientation of the underground object may also be determined using the signature signal generated by the signature signal generating device mounted to the underground object. Orientation information may be encoded on the signature signal or transmitted as an information signal separate from the signature signal. The probe signal may be microwave or acoustic. The signature signal produced by the signature signal generating device mounted to the underground object may be generated either passively or actively. Further, the signature signal may be produced in a manner which differs from the probe signal in one or more ways, including phase, frequency content, information content, or polarization. Also, the signature signal generating device may produce both location and orientation information, without the need for a separate orientation detecting device. Alternatively, orientation and location information may be produced by independent orientation detection and signature signal generating devices.