22 July 1994 Multi-use applications of dual-band infrared (DBIR) thermal imaging for detecting obscured structural defects
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Precise dual-band IR (DBIR) thermal imaging provides a useful diagnostic tool for wide-area detection of defects from corrosion damage in metal airframes, heat damage in composite structures and structural damage in concrete bridge decks. We use DBIR image ratios to enhance surface temperature contrast, remove surface emissivity noise and increase signal-to-clutter ratios. We clarify interpretation of hidden defect sites by distinguishing temperature differences at defect sites from emissivity differences at clutter sites. This reduces the probability of false calls associated with misinterpreted image data. For airframe inspections, we map flash-heated defects in metal structures. The surface temperature rise above ambient at corrosion-thinned sites correlates with the percentage of material loss from corrosion thinning. For flash-heated composite structures, we measure the temperature-time history which relates to the depth and extent of heat damage. In preparation for bridge deck inspections, we map the natural day and night temperature variations at known concrete slab delamination sites which heat and cool at different rates than their surroundings. The above- ambient daytime and below-ambient nighttime delamination site temperature differences correlate with the volume of replaced concrete at the delamination sites.
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Nancy DelGrande, Nancy DelGrande, Philip F. Durbin, Philip F. Durbin, } "Multi-use applications of dual-band infrared (DBIR) thermal imaging for detecting obscured structural defects", Proc. SPIE 2217, Aerial Surveillance Sensing Including Obscured and Underground Object Detection, (22 July 1994); doi: 10.1117/12.179934; https://doi.org/10.1117/12.179934

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