The present invention relates to a system of locating and identifying underground pipes, such as those which carry gas, water and waste to/from homes and building so that, among other things, these pipes can be avoided by excavating equipment or the like. More particularly, the system of the present invention enables the detection of such objects utilyzing, in combination with other novel elements of this invention, ground-probing RADAR.
This invention further relates to the RADAR detection of underground pipes, for example, and more particularly relates to a system which focuses a characteristic hyperbolic RADAR response received from an underground object, such as a pipe or other object, utilizing synthetic aperture type technologies, and further processes same to accurately determine said object's underground position.
Accurate RADAR-based underground object detection has always been an elusive goal because of the variability of the ground as a conducting medium in three dimensions, i.e., inherent variations in ground layers, density, obstructions, dielectric constant, etc. Water content, in particular, acutely varies the ground's dielectric constant which correspondingly attenuates RADAR signals making consistent detection of targets underground difficult at best. Electromagnetic signals transmitted into the ground and reflected from an object buried therein tend to suffer high signal attenuation resulting in low signal-to-clutter and signal-to-noise ratio. Efforts to improve detection ability have found that while a single frequency of operation may be desirable in a particular type soil, the same frequency may be undesirable in another, frequently misinterpreting said objects as ground clutter by conventional underground radar systems.
In an effort to overcome inadequacies of conventional underground RADAR detection, U.S. Pat. No.3,831,173 discloses a ground radar system which utilizes a transient signal comprising a wide variety of radiated frequencies, Due to the use of the transient signal, effective reflections are received from a wide variety of underground objects such as pipes, utility lines, culverts, ledges, etc., to depths around 10 feet. The '173 system, however, while appropriate for detecting small conducting objects, is basically unable to accurately detect non-conducting objects with cross-sections of less than one or two feet.
U.S. Pat. No. 3,967,282 discloses a detector for detecting both metallic and non-metallic objects, based on differences in the dielectric constants of the object and its surrounding medium, in order to give a location of the object. The '282 invention, however, is burdened with difficulty in processing the received data such that accurate object detection and positioning is not achieved.
U.S. Pat. No. 4,706,031 discloses a method and apparatus for identifying a target object located in the ground, in the air or under water. The basis within the disclosure for detection and target identification resides in the apparatus use of the phase deviation between the transmitted and received (echo) radio-wave signals. A signal containing a mixture of various frequencies is transmitted and the return signal or signals are analyzed. A detected difference in phase deviation between the particular frequencies received is used to identify the material properties of the object from which the energy is reflected. The '031 apparatus, however, is still plagued with problems when it comes to detecting small non-conducting objects.
U.S. Pat. No. 4,951,055 discloses a ground probing RADAR which includes means for displaying echo images of a buried material. The displayed images are capable of providing a depth direction of the buried material and a movement direction of a moving vehicle carrying the RADAR. The RADAR includes first means for forming a hyperbolic echo image of the material, and causing a hyperbolic echo image to be displayed on the display means, second means for forming a false echo image and causing the false echo image to be displayed on the display means, third means for inputting data to the second means to cause a displayed position of the false echo image to be shifted so that a vertex position of the false echo image and expansion opening thereof coincide with those of the echo image of the buried material, and fourth means for calculating a propagation velocity of the electromagnetic waves in the ground on the data indicative of the vertex position and opening expansion of the false echo image when the two displayed echo images coincide with each other. A position of the buried material is detected on the basis of the propagation velocity value calculated by the fourth means.
That is, when electromagnetic waves are emitted from a plurality of points on the ground surface above a buried material, an echo image formed on the basis of data of propagation times of reflected waves at their respective points describes a hyperbola as a result of expansion of the transmitted electromagnetic waves. An operation is carried out to overlap, on the echo image, a false echo image lying in the same coordinate system and consisting of a similar hyperbolic image. If the two echo images are overlapped, a vertex position and an expansion of the opening of the echo image can be determined from the data of the false echo image. Thus, the propagation velocity of electromagnetic waves are calculated from the data that represents the vertex position and the expansion of the opening. The position of the material under the ground is then calculated in relation to the data of propagation time in any position.