On the measurement uncertainties of THz imaging systems based on compressive sampling

Abstract

The paper deals with the experimental performance assessment of Compressive Sampling (CS) based Terahertz (THz) Imaging systems, an emerging approach for carrying out non-destructive tests of materials with the aim of detecting defects and flaws. Differently from traditional methods based on raster scan, CS approach allows to reconstruct the image of interest through a reduced number of measurements, with a notable reduction of the time of investigation.Although both simulated and experimental results concerning the performance assessment of THz Imaging technique are available in literature, the additional uncertainty due to the application of CS approach has never been in-depth taken into account, since the step of CS processing has been considered as ideal. Due to the success of CS-based Imaging THz technique and the promising performance of its exploitation also in industrial applications, the considered assumption is no more acceptable. Therefore, the authors focused their attention on the uncertainty sources associated with the experimental application of CS to THz Imaging systems and on their impact on the overall quality of the reconstructed image.Several numerical tests, conducted by means of an optimized design of experiments, allow to (i) assess the sensitivity to relevant uncertainty sources of the reconstructed image quality and (ii) define a suitable performance factor capable of driving experimenters towards a proper configuration of the measurement station. In particular, misalignment of the CS masks turns out to be the most impacting uncertainty source, as confirmed by experimental tests carried out through an actual THz Imaging system. Nevertheless, the performance factor estimated on the reconstructed image of a reference target is capable of highlighting the presence of an incorrect configured Imaging system, thus making it possible to remedy and provide accurate and reliable THz images.