Experimental and methodological work with the underwater antenna Nautilus
We continue to work on the development of the direction of underwater GPR. The goal is to develop a methodology for inspecting hydraulic structures using the OKO-3 Nautilus underwater antenna with a central frequency of 700 MHz.
This time, experimental and methodological work was carried out at the section of the supply canal of the hydroelectric power plants. Our specialists examined the underwater parts of the supply canal and the concrete structures of the banks. In addition to Nautilus, AB-400 and AB-1700 antennas were used for the coastal sections of the canal. Topographic referencing in place was carried out using a differential GPS receiver.
GPR survey was carried out along the parallel profile system. A total of 143 transverse profiles and 7 profiles in the longitudinal direction were made. The total length of the performed transverse GPR profiles (with three antennas) was 1065 linear meters.
GPR survey using AB-700 Nautilus was carried out in profiling mode, in which the device is pressed as tightly as possible to the bottom of the discharge canal and to concrete structures and moves continuously along the observation profile, at a speed of about 3 km/h (the speed of movement depends on the selected survey parameters and surface conditions). During the GPR survey of coastal areas, the antennas were moved over the surface of concrete slabs. The GPR was controlled, the sounding results were saved and the scan results were displayed in real time using the CartScan software.
As a result of the performed experimental and methodological work, the thickness of the lining and sand and gravel layer was determined. The thickness of the lining of the coastal part is about 10 cm, of the underwater part – 15 cm. The thickness of the sand and gravel layer in the underwater part is 40-50 cm, in the coastal part – 60-80 cm. The schemes of the location of defects and the distribution of the contact conditions of the canal lining have been constructed. This will make it possible to correctly carry out work on the reconstruction of the object in the future.