Indoor Full-Body Security Screening: Radiometric Microwave Imaging Phenomenology and Polarimetric Scene Simulation

Abstract

The paper discusses the scene simulation of radiometric imagers and its use to illustrate the phenomenology of full-body screening of people for weapons and threats concealed under clothing. The aperture synthesis technique is introduced as this offers benefits of wide field-of-views and large depths-offields in a system that is potentially conformally deployable in the confined spaces of building entrances and at airport departure lounges. The technique offers a non-invasive, non-cooperative screening capability to scrutinize all human body surfaces for illegal items. However, for indoor operation, the realization of this capability is challenging due to the low radiation temperature contrasts in imagery. The contrast is quantified using a polarimetric radiometric layer model of the clothed human subject concealing threats. A radiation frequency of 20 GHz was chosen for the simulation as system component costs here are relatively low and the attainable half-wavelength spatial resolution of 7.5 mm is sufficient for screening. The contrasts against the human body of the threat materials of metal, zirconia ceramic, carbon fiber, nitrogen-based energetic materials, yellow beeswax, and water were calculated to be ≤7 K. Furthermore, the model indicates how some threats frequency modulate the radiation temperatures by ~±1 K. These results are confirmed by experiments using a radiometer measuring left-hand circularly polarized radiation. It is also shown using scene simulation how circularly polarized radiation has benefits for reducing false alarms and how threat objects appear in canyon regions of the body, such as between the legs and in the armpits.

Microwave Imaging in Security — Two Decades of Innovation

“…Passive image formation relies primarily on radiometric techniques for the receiving and focusing of the radiation field out of the human body [28]. The received energy in this case is composed of a combination of the thermal radiation and the skin reflections from ambient illumination.…”

Experimental Demonstration of Accurate Noncontact Measurement of Arterial Pulse Wave Displacements Using 79-GHz Array Radar

“…Our measurement system can locate the reflection points on the human body and extract the displacement waveforms at those points, whereas the corresponding body parts are not identified. In the future, however, it will be important to obtain the entire shape of the human body using radar imaging [36]- [40] to allow the exact location of each beam spot to be estimated and the corresponding body parts identified.…”

Detection of concealed explosives and shrapnel weapons using decompositions of microwave polarimetric radar data

“…The first is a surrogate shrapnel weapon (31.5 cm long by 12 cm wide by 2.2 cm thick) comprising a collection of galvanised steel felt nails contained in a paraffin wax binder. The second is a slab of beeswax, 3.8 cm thick, chosen as a surrogate explosives weapon, as beeswax is an accurate simulant of a class of nitrogen-based energetic materials [14]. The results of the decompositions are shown separately for the measurements of: a) the weapons by themselves, b) the human torso with no threats present, c) the surrogate threat items on the human torso.…”