3dimensional GPR applied to archeological survey and mitigation of natural disastres
GPR (Ground Penetrating Radar) technology has been widely accepted as shallow geophysical exploration method. We have developed 3DGPR system, which uses high-accuracy positing information together with GPR data actuation, and have demonstrated that it can obtain subsurface 3-dimensional GPR images much clear than conventional GPR surveys. We have applied this method to some archaeological sites in Japan, including Sitobaru, Sakitama and Zuiganji. We could demonstrate that it is not only detection, but also can image subsurface structures. After the 3.11 Great East Japan Earthquake and Tsunami, we have used this method for understanding the geological anomalies caused by the earthquakes.
3DGPR for the Non-Destructive Monitoring of Subsurface Weathering of Sandstone Masonry
Remote sensing techniques, such as LiDAR and photogrammetry, are used by researchers exploring the spatial distribution of weathering features in historic masonry. These well-established tools provide users with a perspective of the processes affecting the surface of masonry blocks; however, they cannot provide information on the alteration occurring subsurface. Geophysical tools are being explored as a potential approach to observe the variation in material properties beneath masonry block surfaces and to examine the patterns of deterioration across wall sections. Applying such techniques inform the development of conceptual models of weathering at the block to building wall scale. In this study, ground-penetrating radar (GPR) was selected to inspect the subsurface condition of the wall section of an historic church wall, where areas of granular disintegration and flaking can be observed. 3DGPR was selected for this task, as its use of regular grids during data collection make it better suited for detecting features within an area. Three high-frequency antennas, 1.2 Ghz, 1.6 Ghz and 2.3 Ghz, were run across the study area in a series of 80 cm by 80 cm grids. The data were collated within GIS, where observed features were annotated onto a schematic of the wall surface. The 3DGPR outputs identified anomalies within this structure that could not have been as easily interpreted using a 2DGPR transect. However, as 3DGPR relies upon interpolative techniques to estimate the returns between observation transects, the validity of features detected in these locations need to be tested. The results of this application of 3DGPR identified variable weathering response across the wall section, relative to elevation. These observations were used to develop a conceptual model linking these findings to seasonal variation in the capillary rise of groundwater, upward from the base of the church wall. Through these findings it is possible to see how GPR can assist in developing our understanding of the processes threatening heritage buildings.
EFFICIENT LARGE-SCALE UNDERGROUND UTILITY MAPPING WITH AMULTI-CHANNEL GROUND-PENETRATING IMAGING RADAR SYSTEM
Ground-penetrating imaging radar (“GPiR”) combines standard GPR with accurate positioning and advanced signal processing to create three-dimensional (3D) images of the shallow subsurface. These images can reveal soil conditions and buried infrastructure. A commercial GPiR called the CART Imaging System was designed for mapping urban infrastructure. The CART system covers a 2m swath on the ground and can collect data while moving at speeds up to about 1km/h. The system collects enough data in a single pass to form a 3D image beneath its track; side-by-side passes are stitched together to create a seamless image of the subsurface.