Buried Marking of Point Locations

An independent system to pinpoint buried equipment to depths of 10 ft has been developed. Its primary use will be rapid, accurate, and unambiguous location of underground utility services and survey points. The system has two components-a passive marker buried at a point of interest, and a hand-carried electronic interrogator. The marker, which is packaged as a sturdy peg, collects and reradiates low frequency energy when simulated by an interrogator. The peg design enhances pick-up range and location accuracy, and allows user identification by frequency. The interrogator is a sequentially switched transmitter-receiver that generates precise energy bursts and detects returned signals; optimum processing by frequency selection and cross correlation is used. The design of both components acknowledges an abusive field operating environment. Interrogator physical and operational details received particular emphasis, resulting in a simple functional instrument of unconventional shape.