ИСТИНА

Large cities growth and aging lead to the irreversible negative changes of underground. The study of these changes at the urban area mainly based on the shallow methods of Geophysics, which extensive usage restricted by technogenic noise. Among others, precision gravimetry is allocated as method with good resistance to the urban noises. Firstly the objects of urban gravimetric survey are the soil decompaction, leaded to the rocks strength violation and the karst formation. Its gravity effects are too small, and their investigation requires the modern high-precision equipment and special measurements methods. The Gravimetry division of Lomonosov Moscow State University helds the tests of modern precision gravimeters Scintrex CG-5 Autograv since 2006. It was examined the main performance characteristics of over 20 precision gravimeters in various operational modes. Stationary mode. Long-term gravimetric measurements on a base station. It shows that records differ by highfrequency and mid-frequency (period 5 - 12 hours) components. The high-frequency component, determined as a standard deviation of measurement, characterizes the level of the system sensitivity to external noise and varies for different devices from 2 to 5-7 mkGals. Midrange component, which closely meet to the rest of nonlinearity gravimeter drifts, partial compensated by the equipment. This factor is very important in the case of gravimetric monitoring or observations, when midrange anomalies are the target ones. For the examined gravimeters, amplitudes’ deviations, associated with this parameter reach 10 mkGals. Various transportation modes - by walk (softest mode), lift (vertical overload), vehicle (horizontal overloads), boat (vertical plus horizontal overloads) and helicopter. The survey quality compared by the variance of the measurement results and internal convergence of series. The measurement results variance (from 2 to 4 mkGals) and its internal convergence are independent on transportation mode. Actually, measurements differ just by the processing time and appropriate number of readings. Important, that the internal convergence is the individual attribute of particular device. For the investigated gravimeters it varies from 3 up to 8 mkGals. Various stability of the gravimeters location base. The most stable basis (minimum microseisms) in this experiment was a concrete pedestal, the least stable – point on the 28th floor. There is no direct dependence of the measurement results variance on the external noise level. Moreover, the external dispersion between different gravimeters is minimal at the point with the highest microseisms. Conclusions. The quality of the modern high-precision gravimeters Scintrex CG-5 Autograv measurements is determined by stability of the particular device, its standard deviation value and the nonlinearity drift degree. Despite the fact, that mentioned parameters of the tested gravimeters, generally corresponded to the factory characters, for the surveys required accuracy 2-5 mkGals, should be selected the best gravimeters. Practical gravimetric survey with such accuracy allowed reliably determine the position of technical communication boxes and underground walkway in the urban area, fixed by gravity minimums with the amplitudes from 6-8 mkGals and width 1 - 15 meters. The holes‘ parameters, obtained as the interpretation result are well aligned with the a priori data.