The possibilities of obtaining numerical estimations of the time of wave propagation and parameters to describe the form of recorded wave impulses, with the use of a sequence of sessions of the monochromatic radiation on various frequencies are investigated. The monochromatic signals are invariant in their form when propagating in the linear media of any complexity. Only two parameters - a phase displacement and amplitude vary. The frequency of signals is preset and kept with a high accuracy.
The difference in phases between the radiated and the recorded signals expresses the propagation time (delay) in a medium modulo, which is equal to its period of signal. A real delay is represented by the sum of an unknown integer of periods and the measured fractional part of a period. The integer part of the delay is calculated with the use of additional measurements on other frequencies. This principle is used in the phase radio engineering bearing and navigational systems operating in the homogeneous (one-wave) medium and differs from impulse systems of the same purpose by a very high accuracy. The objective of the present research is to extend this method to an essentially inhomogeneous seismic medium and to obtain numerical estimations of the times of propagation of separate waves without essential loss in the level of “technical” accuracy of modern equipment for vibrosounding exploration.
In experimental sounding systems of SB RAS, the phase of monochromatic signals at a sufficient duration of sessions is measured by a coherent method with errors about one degree at distances of 300 km. With the frequency of a signal 6 Hz the measurement error of a difference in phases equal to 1 degree corresponds to the time interval 0.5 ms and to the travel of a wave in solid rocks about 2 m.
The essential advantage of vibrosounding methods of exploration over the impulse methods is, that vibrational signals can be specified (synthesized) and to within fractions of milliseconds be reproduced with the help of specialized computer systems of vibrators control. The possibility to multiply radiate signals with practically constant parameters allows one to proceed to the development of sounding systems intended for the research into the field of geodynamics, first of all for the detection and tracing measurements of variations of the tense state of the of the earthquake-prone foci for the sake of earthquake prediction.