Groundwater monitoring by GPR in Mongolia

A controlled water production was performed at a water source of Ulaanbaatar city, Mongolia to evaluate the effectiveness of ground penetrating radar for detecting and monitoring dynamic groundwater movements in the subsurface. The groundwater level in Ulaanbaatar city area is between 2 m-10 m. This relatively shallow depth makes it a suitable target for detection by GPR. Field experiments in Ulaanbaatar were carried out in 2001 with 100 MHz antennae. We measured the groundwater level around a pumping well, then we monitored the change of the level after the pump was stopped. The groundwater level was about 5 m. We could detect the groundwater change about 50 cm, when the water level in the production well changed by 65 cm. If we acquire the data by locating the antenna positions very accurately, we can obtain radar profiles with very high coherency, and we could see the groundwater migration clearly. The CMP was also used in the same site in order to determine the reflection from the groundwater surface. It was found that CMP and velocity analysis give a good information about the depth variation of the groundwater saturation in soil.