Wave Characteristics of Radar Echo Contained Air Void in Shallow Underground

Detecting method of cavity or air void in shallow underground using ground penetrating radar (GPR) is practically important, however, it is seemed that the technique of this depends on to personal experience. The typical difficulties ontheoretical approach are concidered as followes. At first, medium of soil surrounded cavity is extremely random and dispersive property, so the echo from cavity can not generally understand with conventional rules.Another item is property of GPR antenna This is used as wave transmittor and sensor of reflected radar echo from target, but antenna's properties are depended on distance from ground surface and permittivity of medium, so the interpretation of radar echo is extremely become difficulty. We have studied how to detect the air void existence using pulse type radar for several years. The target is considered such as the cavity in seaside bank, a stone box of ancient ruins and void borned by water leakage in a town area. In this paper, we describe about strength of transient electric field excited 1 ns impulse and about statistical property of radar echo and processing for detecting cavity using statistical property.