A.V. Popov – Dr.Sc.(Phys.-Math.), Main Research Scientist, Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of RAS
I.V. Prokopovich – Research Scientist, Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of RAS
D.E. Edemsky – Ph.D.(Eng.), Senior Research Scientist, Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of RAS
P.A. Morozov – Ph.D.(Phys.-Math.), Senior Research Scientist, Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of RAS
A.I. Berkut – Dr.Sc.(Eng.), General Director of JSC VNIISMI (Moscow)
A promising direction of GPR development is increasing its penetration depth in order to meet the needs of the upper crust geology in a 100−200 m subsurface layer. The ways to achieve deep penetration include increasing transmitter power, antennas efficiency, receiver sensitivity, as well as reducing the noise level. All these ideas have been implemented in a series of «Loza» enhanced-power subsurface radars designed at IZMIRAN and partner R&D company VNIISMI. The main distinctive feature of this deep penetrating radar (DPR) is energy accumulation in a single high-voltage transmitted pulse instead of received signal synthesis by repetitive stroboscopic processing. Another construction peculiarity is the use of resistively-loaded antennas, which allows one to come closer to creation of an ideal non-oscillating probing pulse. In order to reach maximum depths, the energy maximum in Loza N DPR is shifted to the lower part of the receiver frequency band 1−50 MHz. As a result of this development, the first hundreds of meter of the underground medium became accessible for GPR survey. In this work, some experimental deep radargrams (B scans and selected A scans) are discussed. A special attention is paid to the protracted signals coming from the depths of 50−100 m. Practical experience of field engineers working with Loza N DPR and comparative analysis of low-frequency radargrams together with check drilling reveal a reliable correlation between the sign of these weak return pulses with vertical gradients of the subsurface medium. The developed visualization methods allow an experienced user to detect and localize useful or dangerous geological or man-made subsurface structures (ore bodies, karst voids, landslides, tunnels, etc). In the last section, an asymptotic description of the probing pulse partial reflections from smooth permittivity gradients is derived to confirm these observations. Model examples demonstrate a remarkable similarity between the calculated and measured A scans. Although approximate solutions of the quasi-monostatic GPR probing problem are known for a long time their implementation is usually restricted to a piecewise-uniform permittivity distribution. Backward reflections from a smooth transition layer may be exponentially small, which requires a big number of thin uniform layers and inadequately large computation time for their correct assessment. In this relation, our asymptotic solution has an advantage of simplicity and clear physical meaning necessary for qualitative understanding of the DPR field data.
- Kopeikin V.V., Edemsky D.E., / Garbatsevich V.A., Popov A.V., Reznikov A.E., Schekotov A.Yu. Enhanced power ground penetrating radars // Proc. 6th Internat. Conf. on GPR. Sendai (Japan). 1996. P. 152−154.
- http://www.geo-radar.ru/ (data obrashheniya 20.02.2018).
- Kopeikin V.V., Krasheninnikov I.V., Morozov P.A., Popov A.V., Guangyou Fang, Xiaojun Liu, Bin Zhou. Experimental verification of LOZA V GPR penetration depth and signal quality // Proc. of 4th Internat. Workshop on Advanced GPR. Naples (Italy). 2007. P. 230−233.
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- Giannopoulos A. Modelling ground penetrating radar by GprMax // Construction and Building Materials. 2005. V. 19. P. 755−762.
- Vinogradov V.A., Kopeikin V.V., Popov A.V. An approximate solution of 1D inverse problem // Proc. 10th Internat. Conf. on GPR. Delft (The Netherlands). 2004. P. 95−98.