Surface and subsurface inspection of concrete structures provides useful information for the maintenance of these structures. Remote sensing techniques such as radar and microwave sensors enable engineers to assess structural condition with ease and efficiency. This paper reports the performance of a 10.5 GHz portable imaging radar system for the quantitative, surface, and subsurface sensing of concrete structures in field configuration. Ranging, size determination, crack imaging, and subsurface interface determination are conducted using stripmap synthetic aperture radar (SAR) images. Three concrete structures are selected for field measurements. Ranging accuracy, size determination procedure, and effect of background noise are studied. Issues with background subtraction are discussed. Image-based, quantitative condition assessment criteria for ranging and size determination are proposed.

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The use of microwave and radar sensors in the nondestructive evaluation (NDE) of damaged materials and structures has been proven to be a promising approach. In this paper, a portable imaging radar sensor utilizing 10 GHz central frequency and stripmap synthetic aperture radar (SAR) imaging was applied to steel and wood specimens for size and range determination. Relationships between range and properties of SAR images (e.g. maximum amplitude and total SAR amplitude) were developed and reported for various specimens including a steel bar (2.5 cm by 2.5 cm by 28.5 cm), a wood bar (2.5 cm by 2.5 cm by 28.5 cm), a steel plate (39.7 cm by 57.9 cm by 1.75 cm), and a wood board (30.5 cm by 30.5 cm by 1.8 cm). Various ranges from 30 cm to 100 cm were used on these specimens. In our experiment, attenuation of radar signals collected by the imaging radar system on different material specimens was measured and modeled. Change in the attenuation of maximum SAR amplitude was observed in different materials. It is found that SAR images can be used to distinguish materials of different compositions and sizes.

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