Abstract-How do detected objects affect the noise distribution of Terahertz security images?

Zhaodi Wang, Menghan Hu,   Ercan Engin Kuruoglu,  Wenhan Zhu,   Guangtao Zhai,

https://ieeexplore.ieee.org/document/8418702/

The purpose of this study is to analyze how detected objects affect the noise distribution of THz security images. Noise in THz image caused by hardware deteriorates the image quality seriously, limiting the application. In addition, there are few papers on the noise analysis of THz screenings. Due to the special attributes of the THz image compared to the natural image, an alpha-stable distribution is used to fit the noise of THz image instead of the commonly-used Gaussian distribution. The database used in this study is composed of 181 THz image cubes with a test object as well as 2 empty image cubes. After analyzing the four parameters of alpha-stable distribution, we can observe that the noise patterns of THz images are indeed different from those of natural image obtained by RGB camera. The possible reasons are given based on the principles of the THz imaging device. The analysis of the distribution of four parameters of alpha-stable model demonstrates that there exists a nonlinear effect due to the change of reflected wave’s pattern caused by the body structure. This study provides an efficient and flexible model for THz images and a useful guidance for the design of THz image denoising algorithms and the development of imaging hardware.

Abstract-The Role of Scattering in Quasi-Ordered Structures for Terahertz Imaging: Local Order Can Increase an Image Quality

Irina N. Dolganova, Kirill I. Zaytsev,  Stanislav O. Yurchenko, Valeriy E. Karasik, Valery V. Tuchin

https://ieeexplore.ieee.org/document/8371640/

In this paper, we propose a computational approach for description of radiation transfer in a quasi-ordered medium and study the impact of scattering on electromagnetic wave propagation and image formation. It combines finite-difference time-domain method, Monte Carlo simulations, and radiative transfer theory. Using as an example terahertz imaging, we analyze modulation transfer function (MTF) of imaging system operated at 0.25 THz for scattering material layers placed between the object and the imaging plane. We experimentally study imaging of bar-pattern test-objects through a quasi-ordered scattering medium. Both numerical and experimental results are in good agreement and demonstrate an impact of quasi-ordered scatterers on quality of THz images, i.e. particular combination of the electromagnetic wavelength and parameters of scattering materials could enhance MTF compared with ones with random particle structures.