Existing terahertz THz systems for detecting concealed explosives are not capable of identifying explosive type
which leads to higher false alarm rates. Moreover, some of those systems are imaging systems that invade personal
privacy, and require more processing and computational resources. Other systems have no polarization preference
which makes them incapable of capturing the geometric features of an explosive.
In this study a non-imaging polarized THz passive system for detecting and identifying concealed explosives
overcoming the forgoing shortcomings is developed. The system employs a polarized passive THz sensor in
acquiring emitted data from a scene that may have concealed explosives. The acquired data are decomposed into
their natural resonance frequencies, and the number of those frequencies is used as criteria in detecting the explosive
presence. If the presence of an explosive is confirmed, a set of physically based retrieval algorithms is used in
extracting the explosive dielectric constant/refractive index value from natural resonance frequencies and amplitudes
of associated signals. Comparing the refractive index value against a database of refractive indexes of known
explosives identifies the explosive type.
As an application, a system having a dual polarized radiometer operating within the frequency band of 0.62- 0.82
THz is presented and used in detecting and identifying person borne C-4 explosive concealed under a cotton
garment. The system showed higher efficiencies in detecting and identifying the explosive.
A model is developed to relate the attenuation through a vegetation canopy, to the geometric and dielectric parameters of the canopy constituents. The model is designed to operate over a wide frequency band in the microwave region and include both deciduous and coniferous trees. The vegetation canopy is represented by a discrete random layer of cylinders and disks having the same geometric and dielectric properties as the vegetation canopy constituents. The Foldy-Twersky Integral Equation is used to relate the attenuation to the scattering amplitude of the vegetation constituent evaluated in the forward direction. Numerical results are presented to show how the level and frequency dependance of the attenuation depend on type of vegetation constituent and its orientation.
A mathematical evaluation of the potential of active microwave sensors for monitoring underground permafrost is carried out. For this purpose, the Helmholtz Integral is used to relate the scattered field to the field inside the permafrost. A mathematical formation is derived for the scattered field by estimating the inner field through a generalized Rayleigh- Gans approximation. Numerical calculation show that the freezing thawing process is the dominant factor determining the relative level of the backscattered signal.