Hidden Object Detection and Recognition in Passive Terahertz and Mid-wavelength Infrared

M Kowalski

doi:10.1007/s10762-019-00628-7

Abstract

The study presents the comparison of detection and recognition of concealed objects covered with various types of clothing by using passive imagers operating in a terahertz (THz) range at 1.2 mm (250 GHz) and a mid-wavelength infrared (MWIR) at 3–6 μm (50–100 THz). During this study, large dataset of images presenting various items covered with various types of clothing has been collected. The detection and classification algorithms aimed to operate robustly at high processing speed across these two spectrums. Properties of both spectrums, theoretical limitations, performance of imagers and physical properties of fabrics in both spectral domains are described. The paper presents a comparison of two deep learning–based processing methods. The comparison of the original results of various experiments for the two spectrums is presented.

Highlights

Namely thermal infrared (IR) and terahertz (THz), may provide images visualising objects placed on a human body covered with clothes
The results show that the presented detection method works better for mid-wavelength infrared (MWIR) images, but only at the beginning of the experiment
Terahertz cameras can visualise a hidden object mainly due to a non-zero transmission through clothing, whereas thermal cameras cannot utilise this property because the transmission rate through clothing is negligible

Summary

Introduction

Non-intrusive detection and recognition of objects concealed under clothes remains challenging in terms of sensors and processing algorithms. Namely thermal infrared (IR) and terahertz (THz), may provide images visualising objects placed on a human body covered with clothes. Both spectra rely on different phenomena and provide images of different qualities. The most useful property of imagers operating in terahertz range is the ability to see through clothing thanks to high transmission of terahertz waves through popular textiles. Thermal infrared imagers are able to detect small temperature differences on the object’s surface.

Objectives

Methods

Results

Conclusion