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Object locating system
| Details |
Inventors: Arndt, G. Dickey; Carl, James R.;
Assignee: The United States of America as represented by the Administrator of the (Washington, DC)
Primary Examiner: Snow; Walter E.
Assistant Examiner:
Attorney, Agent or Firm: Barr; Hardie R.
A portable system is provided that is operational for determining, with three dimensional resolution, the position of a buried object or a proximately positioned object that may move in space or air or gas. The system has a plurality of receivers for detecting the signal from a target antenna and measuring the phase thereof with respect to a reference signal. The relative permittivity and conductivity of the medium in which the object is located is used along with the measured phase signal to determine a distance between the object and each of the plurality of receivers. Knowing these distances, an iteration technique is provided for solving equations simultaneously to provide position coordinates. The system may also be used for tracking movement of an object within close range of the system by sampling and recording subsequent positions of the object. A dipole target antenna, when positioned adjacent to a buried object, may be energized using a separate transmitter which couples energy to the target antenna through the medium. The target antenna then preferably resonates at a different frequency, such as a second harmonic of the transmitter frequency. |
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DETAILED DESCRIPTION The proximate object locating system and method of the present invention may be used in air but may also be used in substantially solid materials such as a wide variety of soils or earth formations having different conductivities and relative permittivities.
The proximate object locating system is more accurate in air or space because such media are highly homogenous and uniform.
The present invention and method operates quickly to provide an accurate relative position of buried objects, such as buried natural gas pipelines.
A method for locating a buried object is disclosed that comprises: determining an indicia of relative permittivity of material in which the object is buried, selecting a transmitter frequency that is (1) low enough to provide sufficient soil penetration based on the indicia of relative permittivity and (2) high enough to keep the transmitting antenna length less than about one meter in length, selecting a marker antenna for reradiating a signal with a frequency having sufficient soil penetration to be detected at the surface as determined from the conductivity, positioning a marker antenna in the vicinity of the buried object, and detecting the reradiated signal from the marker antenna.
The method may provide for one or more of the following actions such as: determining an indicia of conductivity of material in which the object is buried, detecting the reradiated signal from the marker antenna using at least two receivers, measuring the phase of the reradiated signal detected with the at least two receivers, determining a distance between the marker antenna and each of the at least two receivers, determining the relative position of the marker antenna from the distance between the marker antenna and each of the at least two receivers, moving the marker antenna through the object, and selecting the marker antenna to reradiate a harmonic of the transmitter frequency.
The method may also include such steps as determining signal loss from a transmitter to a marker antenna to a detector, adjusting system component size such that the signal loss is acceptable for detecting a reradiated signal, using a dipole antenna to reradiate a signal at a harmonic of the transmitter frequency, and suppressing any second harmonic signal from a transmitter
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