Investigation of geoelectric parameters of rock

Abstract

Sub-surface investigation of small objects predetermines a necessity of increasing the nominal values of sounding frequencies. In this connection investigation of the embedding medium in the decimeter wavelength range is of significant interest.

For the solution of the problem a technique for the determination of geoelectrical properties of rock in 500…2000 MHz frequency range was developed and approved. In addition, investigation was conducted by the method of radioscopy of separate rock-massif blocks located at the earth surface for the determination of a reflection coefficient value.

The tests were carried out at the surface of the investigated rock massif and in the adit with the use of horn antennas. The horn antenna, disposed in the adit, was fastened to the vault, distance to its wall being 5…10 cm. The receiving antenna was placed at the earth surface, the thickness of topsoil over the rock massif being 3…5 cm (thin soil layer, moss, plan roots).

As a result of measurements, it was obtained that the resolution of electromagnetic field with thickness of rock about 6 meters has a value from -85 to -95 dB in the range of 500…2000 MHz. The validity of the measurements was influenced by metal objects diffraction, multiple reflection, interference from a supply line and telephone network lines, etc. Loss angle tangent was calculated based on the results of attenuation coefficient measurements and the data about the thickness of the medium subjects to radioscopy.

For the investigation of the structure of the sub-surface earth layers in the decimeter wavelength range, it is necessary to have a transmitter power of the order of ten watts and directive antennas.