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Health and Safety Plan 1319 & 1327 South Madison Street, Stockton,CA 432770 64 El Consultants or asphalt is also a popular GPR application. GPR operates on the principle that electromagnetic waves emitted from a transmitter antenna are reflected from buried objects having different electrical properties than the host material. The signals detected at the receiver antenna are recorded and provide a detailed cross section of the subsurface that is similar in appearance to a seismic reflection record. The depth of penetration of the radar pulse is controlled by site conditions and the frequency of the antenna chosen. For utility locating, depth is usually limited to 10 feet or less to ensure safe drilling operation. Transducers exist that can penetrate to greater depths, but these use a lower frequency. Lower frequency means lower resolution,and narrow objects like utilities cannot be seen. Some things to consider when evaluating GPR: • Closely spaced survey lines are required to locate small objects, • A relatively smooth surface is also necessary,and • GPR is not as effective where the ground surface is paved with highly reinforced concrete due to interference from the presence of the metal rebar. • Interference is also prevalent if surface structures are immediately adjacent to the area. Ground Penetrating Radar ir Pipe Tracing A pipe and cable locator and tracer can be used to detect and trace metallic utilities, utility tracing wires,or warning tapes. In pipe and cable tracing mode,the transmitter can be coupled by direct contact(conductively)to exposed portions of a metallic pipe,cable,or wire,or by simple proximity (inductively)to a subsurface metallic utility with known location and orientation.The transmitter remains stationary and energizes or excites the metallic utility to be traced with a signal that can be traced at the ground surface using the mobile receiver wand or probe. To use the transmitter in the most effective manner, all metallic pipes to be traced must be available for connection directly to the transmitter.The inductive mode is not as effective.Also, the detection is limited to metallic objects and is not useful for plastic, ceramic, or fiberglass utilities.