Space-time versus frequency domain signal processing for 3D THz imaging

For the first time, to the best of the authors knowledge, a 3D image reconstruction is developed using wide beam THz radiation. The reconstruction method finds its origins in the domain of radar and sonar where it is known as Synthetic Aperture Radar (SAR) and Synthetic Aperture Sonar (SAS) respectively. The extension to the SAR/SAS reconstruction algorithms on wide beam terahertz radiation results in a high-resolution 3D image by combining the depth information (due to the penetration aspect of THz radiation) with a 2D scanning setup. Two 3D reconstruction algorithms have been developed, one in the space-time domain and one in the frequency domain. They both have been validated and analysed using simulated data: the azimuth resolution dependence - on the transmitted frequency and on the opening angle - is compared between the space-time and the frequency domain algorithm as well as their respective computational load. The application of the proposed imaging techniques lays in the domain of non-destructive testing (NDT) in particular for composite aircraft samples.