We are doing GPR research with an OYO Georadar unit, using it in a salt mine in Texas and in a potash mine under the North Sea in England. Rocksalt samples from this Texas mine have been measured to show a tan d of 2 x 10-5 by the U.S. National Institute of Standards and Technology in Boulder, Colorado. This is 5 times less lossy at 200 MHz than teflon, the best man-made dielectric used in coaxial cables. Thus we should expect large GPR ranges in rocksalt, and indeed, we found ranges to 62 m, the maximum time scale (1000 ns) for the Georadar unit. Figure 1 shows an example of a GPR record obtained in the Grand Saline salt mine owned by Morton Salt Company. The time scale is 1000 ns (62 m of depth) the profile length is 51 m and the arrows show two saltair interfaces beneath the floor of an upper-level mining operation. The horizontal line across the whole record is an artifact of the system on the 1000 ns mode only. Figure 2 shows a GPR profile in another salt mine location with three different levels of salt-air interfaces caused by previous mining operations. The Georadar artifact is not present. The time scale is 300 ns, equal to a maximum radar range of 18.6 m in salt; the profile length is almost 100 m.


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