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Short‐pulsed terahertz imaging techniques have found application in recent years especially in the areas of nondestructive evaluation, homeland security and biomedical imaging. One such application involves the inspection of bonding between spray on foam insulation (SOFI) and the external tank in the NASA space shuttle. This work discusses a suite of image enhancement techniques that was developed to improve the probability of detection of voids and disbands SOFI. Physics based defect detection and profiling methods are detailed along with initial results. In addition a ray‐tracing model was developed to simulate the inspection process. Results comparing the model and experimental images will also be presented.

Terahertz imaging techniques are beginning to find many applications in areas such as nondestructive evaluation, biomedical imaging and homeland security. The NASA spray on foam insulation (SOFI) inspection is a critical application where terahertz imaging is used to detect disbonds and delamination between SOFI and the substrate metal (external tank). This paper discusses a ray-tracing model for the high frequency inspection system. Model based inversion techniques for the characterization of defects is also proposed

Terahertz imaging is a relatively new technique for sub‐surface imaging using radiations in the spectral range between 0.1 to 10 THz. The technique has been used to image artificially induced inserts simulating disbonds in metal‐foam interfaces and has shown significant promise as a possible non destructive evaluation technique for evaluating the bonding quality of foam. The data in these cases is obtained by scanning across a surface on top of the foam coated on metal structures and collecting the time signal in a window of interest at each point in the scan plane. Proper data processing and visualization techniques become critical in being able to detect the disbonds and delaminations that, additionally, become convoluted due to the wide variety of artifacts and support structures that occur on the metal substrates. In this work we discuss a wavelet based signal enhancement algorithm that provides an effective scheme for visualizing the imaging data and provides a very high contrast between disbonded areas and normal substrate. The technique also shows promise as a first step towards automatic detection and classification of the disbonds. Some preliminary results, obtained on data collected using simulated disbonds that demonstrate the usefulness of the algorithm will be presented.

Significant advances made in the field of Terahertz Imaging have captured the attention of many applications including industrial NDE, biomedical imaging and homeland security. The NASA spray on foam insulation (SOFI) inspection is one such critical application were Terahertz imaging is used to detect disbonds and delamination between SOFI and the substrate metal (external tank). This paper discusses modeling aspects of the high frequency inspection system. The feasibility of using a simple ray‐tracing model is studied. The efficiency of the model is demonstrated by comparing the model prediction with experimental measurements and further using it in an iterative inverse problem scheme for defect reconstruction.