D.E. Edemsky – Ph.D.(Eng.), Senior Research Scientist, Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of RAS
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
V.A. Garbatsevich – Head of Laboratory, Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of RAS
GPR deployment on a flying machine allows one to substantially extend the application area of this geophysical method and to simplify carrying out large surveys of dangerous and hard-to-reach terrains, where usual ground-based methods are hardly applied. There is a necessity to promote investigations in this direction by refining hardware characteristics and developing specific methods and software. For this purpose, we upgraded commercial ground-based subsurface sounding hardware and performed corresponding computer simulation and realistic experiments. Finally, first flights with the constructed prototypes were done with Mi-2 helicopter.
Using our experience in the developing ground-based GPR and the results of numerical simulation, an appropriate configuration of antennas and their placing on the flying machine were chosen. Computer modeling allowed us to choose an optimal resistive loading of transmitter and receiver dipoles; calculate radiation patterns on fixed frequencies; analyze the efficiency of different conductor diameters in antenna circuit; calculate cross-coupling of transmitting and receiving antennas with the helicopter.
Laboratory experiments to check the efficiency of the designed system were performed on an urban building site, using a tower crane with luffing jib to position the measuring system in the air above the ground area to be sounded. Both signals from the surface and subsurface objects were registered. To interpret the results, numerical modeling was carried out. A two-dimensional model of our experiment was simulated, it gave good results compared to the experimental data. Laboratory experiments provided an opportunity to estimate the level of spurious reflections from the external objects, which helped to recognize weak signals from subsurface objects in GPR surveys under live conditions.
The airborne GPR and its antenna system were tested in real-world conditions near the Bolshoe Gryzlovo airfield in Kalyzhskaya province. The payload was placed under the helicopter at a 12 m distance. A powerful pulse transmitter of 10 kV was used, the width of the probing pulse was about 7 ns, the repetition rate around 1 kHz. The receiver with a bandwidth of 20…350 MHz provided the sampling frequency of 1 GHz, synchronization was performed by the aerial signal. As one can see from the following data, all contrast subsurface objects along the helicopter’s path were registered by the airborne GPR and their radio images can be clearly decrypted. Sub-horizontal interfaces in the near-surface ground were not observed, due to their absence at 5…10 m depths confirmed by the ground measurements. The detection of subsurface contract objects shows the efficiency of the developed hardware and applicability of the airborne GPR for real-world subsurface surveys.
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