GPR investigation of the structure of Sendai Castle by CMP method

摘要

The common midpoint (CMP) technique usingground penetrating radar (GPR) was applied to detect the structureand the distribution of an underground stone wall in Sendai Castle.Targets to be detected are buried stones and layers of soil fill,which are distributed from the ground surface to approximately20m in depth. 10 and 11 CMP gathers were recorded on twosurvey lines. The operation frequency of the radar system was from0.3 to 120.3 MHz. Signals from steel objects on the groundsurface was suppressed greatly by two-dimensional f-k filteringand by CMP stacking.By noise removal, velocity analysis, normal moveout correctionand stacking, the images of the subsurface were obtained. Thestructures under the two lines are clearly shown, the structureunder Line 1 is simpler than that under Line 2. The positions ofstones at about 4.1 m and 6.1 m deep under Line 2 are estimatedfrom the relation between time and depth derived from the Dixformula. There is no stone wall under Line 1. The interpretationresult was consistent with the excavation quite well.