Holographic Subsurface Radar as a Device for NDT of Construction Materials and Structures

A relatively rare type of subsurface radar – holographic radar – is described in this paper as a tool for non-destructive testing (NDT) of construction materials and structures. Its principle of operation, advantages and disadvantages are considered. Holographic subsurface radar, operating several discrete frequencies, is used to illuminate a suffi ciently extensive area of a surface of opaque dialectical medium to be inspected to register interference between refl ected from objects and reference waves. In a lossy media with low level of microwaves attenuation, reconstruction algorithms could be applied for obtaining the subsurface image in such a manner as in optical holography. An attempt is made to highlight significant application areas and problem cases where this type of radar could potentially be applied as a device for NDT of construction materials and structures. The paper describes results of different building surveying including objects of historical heritage. Space shuttle thermal protection system tiles were investigated in some other experiments. Each application area is illustrated by relevant data acquired in laboratory experiments or fi eld tests.