| Precise positioning is needful for the detailed mapping of near-surface deformation structure in embankments or beneath the roadways, because the surface undulation and inclination even though small would affect the resolution of anomaly structure. Network service of not only GPS but also GLONASS data, provided by Geospatial Information Authority of Japan, received about 1,300 GNSS stations located at an average interval of about 20 km throughout Japan, enabled us to set a VRS nearby a survey site, and to determine the precise positions of the GPR antenna within several centimeters accuracy. We assembled an RTK-GNSS antenna with a GPR cart and conducted detailed surveys on a full-size model of reinforced soil wall which was damaged by the 2011 East Japan Earthquake, and on a deformed road embankment which was overlaid at least three times. We successfully delineated a deformed surface of upper road embankment and confirmed the consistency between the imaging result by GPR and the visual observation by excavation. The results demonstrated that GPR measurements aided by VRS RTK-GNSS were quite helpful for the detailed 3-D imaging of deformation structure of the near surfaces. As future tasks, we aim to develop the high resolution GPR system incorporating with RTK-GNSS, system of which is easily operated and simply analyzed by everyone. Consequently, we are going to develop some peripheral devices, for example, installation tool of GNSS antenna, monitor for GPR tracks and installation of inclined meter for correcting GPR antenna position. |
