Ground penetrating radar surveys on the ancient Dengfeng Guanxingtai observatory, China

Ground penetrating radar (GPR) surveys were conducted over the ancient Guanxingtai observatory in Dengfeng, Henan Province, China. Located in the Town of Gaocheng, 15 km southeast of Dengfeng City, Henan Province, the Guanxingtai Observatory is the earliest one of its kind so far extant in China, and is also one of the earliest buildings for astronomical observation in the world. It is a UNAVCO World Heritage Site, one of the Historic Monuments of Dengfeng in `the Center of Heaven and Earth'. In fact there is a building cluster around the Guanxingtai Observatory, built on a plot of 0.59 km² and with a floor area of 657.41 square meters. GPR field campaigns were conducted in 2009 on the walls of the Guanxingtai Observatory with the 500-, and 900-MHz GSSI SIR-2 system. The GPR survey results show that the brick layers have dielectric constant ranging from 10.5-12, with a thickness of 0.57-0.6 m. There is possibly a refilled mortar layer behind the brick layer; strong diffractions are displayed in the radargrams for this layer.