| 摘要 |
Cracks in bridges or other structures are detected by applying a thermal gradient to the test structure in a selected region so heat flows from left to right. A first image of the thermal gradient with heat flowing from left to right is taken and stored for further processing. Next a thermal gradient is applied so heat flows from right to left through the selected region. A second thermal image is taken and stored of the heat flowing from right to left. An image taken before a thermal gradient is applied is subtracted from the first and second images to remove thermal reflection and non-induced gradients from the stored images. Each differentiated image is then normalized by dividing each pixel of the differentiated image by the total photon flux from the undifferentiated image. The second image is than subtracted from the first image producing a third image which highlights features which produce thermal gradients of opposite signs. Paint chips and paint drips and other variations in surface emissivity which can produce the appearance of a thermal gradient have the same apparent gradient when heat is applied from either side. Thus the technique of utilizing two temperature gradient images where the gradient is applied from opposite sides uniquely highlights real defects.
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