Near-surface Objects Research Articles

Tectonics and gravity field structure of Central Kazakhstan

Purpose. Identification of the nature of the manifestation of tectonic elements of different ages in Central Kazakhstan in gravitational fields based on the results of the calculation of regional, intra-crustal and local transformants. Methodology. Synthesis and analysis of the data on integrated interpretation and modeling of gravitational, geomagnetic, geothermal fields, the latest movements of the Earth’s crust and parameters of the seismic regime, tectonics and stratigraphy of rocks. Findings. Regional, intra-crustal and local heterogeneities in the lithosphere manifest themselves differently in blocks of Precambrian rocks, Early and Late Caledonides, Early and Late Hercynides. They may be associated with the processes of Paleozoic intracontinental rifting, with the rise of mantle matter and its emplacement into the Earth’s crust, followed by the manifestation of Late Paleozoic orogenesis, doubling of the thickness of the Earth’s crust, outpourings of magmatic formations. Originality. It is established that large gravitational minima are distinguished in areas with Hercynian folding, characterized by abnormally high amplitudes in the movement of the Earth’s crust. In the regions of the Caledonian folding, the values of gravity field anomalies of intermediate intensity and increased amplitudes of the latest movements of the Earth’s crust are manifested. Areas with Pre-Paleozoic folding have relative maxima of gravitational anomalies and minimum values of the latest movements of the Earth’s crust. Earthquake sources are concentrated in the consolidated crust at the junction of areas with different ages of basement consolidation, in gradient zones of geothermal, geomagnetic and gravitational anomalies. According to the variations of the intra-crustal transformant, it was found that a wide range of changes in the values of the gravitational field corresponds to areas with minimal temperature values, whereas in areas with increased temperature values, the range of changes in the values of gravity anomalies is reduced. The distribution of the local transformant of the gravitational field indicates the existence of highly variable anomalies, which reflects the high-frequency gravitational effect of near-surface objects of the Earth’s crust. Practical value. The distribution of inhomogeneities in the lithosphere with various density, geomagnetic and geothermal anomalies of geophysical fields, the nature of the seismic regime and the latest movements of the Earth’s crust predetermined the formation of geostructures with different types of mineralization, each of which is recommended to be searched and explored by a specific rational set of geophysical methods.

Experimental Optimization of the Energy Characteristics of a Ground Penetrating Radar with Continuous Linear-Frequency-Modulated Radiation

In recent years, research has been actively carried out aimed at developing the concept of construction and ways of technical implementation of ground penetrating radars with continuous wave linear-frequency-modulated (LFM) radiation. The key prerequisites for the creation of such systems are the complex consideration of the operating conditions of the radio channel in the near field, including the features associated with multichannel leakage of the probing signal components into the reception path, the presence of multipath reflections from the covering surface, the variable speed of the electromagnetic wave, and the provision of linear processing of a continuous group broadband radio signal with large dynamic range. The paper proposes and describes a scheme of a laboratory stand for LFM GPR research and optimization of the energy characteristics in modes with critical levels of reflections. The results of experiments on the analysis and optimization of the parameters of the end-to-end transfer characteristic of the radio channel are presented. Response studies were performed for two types of antennas at different suspension heights. The responses of the system to an increase in the durtion of the probing pulse and a change in the type of window function were evaluated. An empirical dependence of signal losses during propagation in radio channels of LFM GPR has been established. The conducted studies will improve the energy characteristics of ground penetrating radars with continuous LFM radiation by increasing the detection efficiency of shallow and near-surface objects.

Detection of road cavities in urban cities by 3D ground-penetrating radar

Cavities under urban roads have increasingly become a great threat to traffic safety in many cities. As a quick, effective, and high-resolution geophysical method, ground-penetrating radar (GPR) has been widely used to detect and image near-surface objects. However, the interpretation of field GPR data remains challenging. For example, it is hard to distinguish reflections caused by road cavities or other urban utilities with a conventional 2D GPR survey. The superiority of 3D GPR in data interpretation is demonstrated by a laboratory experiment. Two pipes and a glass-made cavity buried in a sandpit show similar hyperbolic reflections in the 2D GPR profiles; thus, they are difficult to discriminate. In contrast, their geometric shapes and dimensions are readily identified in the 3D image reconstructed from the synthetic 3D GPR data set. Based on these ideas, we have developed a car-mounted 3D GPR system with two antenna arrays oriented in different polarization directions and have detected more than 100 cavities in three Chinese cities over the past year. The field data of two such cavities are presented. As a result, the cavity depth, horizontal size, and height can be accurately estimated from the 3D GPR data set. Laboratory and field experimental results indicate that 3D GPR possesses potential in the detection and recognition of road cavities and utilities in the complex urban environment.

Non-Destruction Method for Detecting Corroded Underground Pipe Using Ground Penetrating Radar

Ground-penetrating radar (GPR) is a geophysical method that can accurately map the spatial extent of near-surface objects or changes in soil. It also produce radargram of those features. The demand for underground utility mapping in Malaysia is increasing rapidly for construction and non-construction activities. However, implementation of GPR in detecting corroded underground pipe in Malaysia can considered unpopular due to less exposure and exploration. Over the time, underground utility pipe will undergo corrosion process. Thus, is it relevant to detect old corroded pipe using GPR? On this basis, the aim of this experimental study was to validate the condition of corroded pipe by comparing its radagram profiles and to evaluate the significant signal reflectivity which were tested on three different pipe condition, namely new, average and old corroded pipe. The result of GPR calibration and data on GPR were processed using Reflex 2D software. In this study, with the aid of Time-Domain Reflectometry (TDR) sensor was used to obtain the soil moisture as it is one of the biggest in fluent to corrosion activity. In the GPR method, radar antennas moved along the ground in transects (B-scan), and two-dimensional profiles of a large number of periodic reflections (A-scan) were obtained. As conclusion, these GPR datasets and soil moisture from TDR reading are evaluated and been analysed thoroughly. At the end of this paper, it is suggested that GPR is efficiently can be used to detect corroded pipe.

Detecting near-surface objects with seismic waveform tomography

Three shallow, high-velocity, rubble-filled targets are imaged using waveform tomography in an engineering-scale clay embankment at Seven Sisters Falls, Manitoba, Canada, to locate targets buried at approximately [Formula: see text] as a blind test of geophysical imaging methods. Previous studies use near-offset reflection methods to image the targets; however, this test uses waveform tomography of the long-offset, refracted arrivals to image P-velocity and seismic attenuation. The targets are invisible to standard traveltime tomography. Using weight-drop data, with frequencies of 20–150 Hz, the subwavelength targets are resolved in the velocity images and complementary images of seismic [Formula: see text] are produced. The interpreted target locations are consistent with limited survey information from the embankment construction. Multiple quality-control efforts, paired with a very good fit between model and observed data, indicate the reliability of the results.

Radar sensing of thin surface layers and near-surface buried objects

A robust ground penetrating radar (GPR) signal processing approach is developed and applied to the sensing of surface soil and ice/water layers as well as near-surface buried objects. The principal technique relies on a reference set of waveforms, which are tested for optimal matching with measured radar reflections to be analyzed. In principle, the reference set can be based on measurements as well as on model output, with the latter employed. Even when layers are quite thin relative to the incident wavelength or pulse, the approach provides accurate information on layer characteristics, particularly thickness. The method assumes a well-defined transmit signal and hence is best used with antennas elevated shove the surface, In tests using UHF pulses on lab and field ice and on thawing soil, the system offers approximately an order of magnitude improvement in layer resolution relative to more traditional methods. Also, in the process of its signal-matching calculations, the procedures provide a numerical indication of the reliability of each result. In application to thawing soil, simulations suggest that one can address a wide variety of conditions using quite a limited set of reference signals. By detecting the thin-layer effect from soil over a buried metallic object, the system also locates near-surface targets when their reflections cannot be separated in time from ground surface returns. An alternative system also succeeds in detecting near-surface objects under the same conditions by detecting wavelet dispersion. This is done without reliance on specific details of transmit wavelet or reflected signals. A mine-like target is detectable in a wet clay soil when the ground is frozen but not when it is thawed.