Experimental uses of short pulse radar in coal seams

Abstract

We discuss here a series of radar tests conducted to determine the penetration distances and reflection ranges obtainable in coal with currently available short‐pulse radar. The various field tests were conducted in 1977 and 1978. Three different types of tests were presented. The first series of tests examined the penetration distances, velocity of propagation, and attenuation versus frequency in a large coal pillar. The velocity of propagation was approximately half that in the air. The tests showed that it was possible to transmit electromagnetic (EM) energy in the range of 20 to 500 MHz through 50 ft of coal. The tests also showed the definite polarization effects that had previously been measured in coal. The second series of tests was designed to show the maximum reflection distances for radar with a center frequency of 100 MHz. Using common‐depth‐point (CDP) reflection techniques, a tenfold CDP line obtained reflections for distances greater than 50 ft. The final series of tests was conducted to locate a six‐inch borehole within a coal pillar. The radar system located the hole quickly and easily even though it was 20 ft into the pillar. These tests have shown that it is possible to use short‐pulse radar to probe coal seams before mining.