Wideband millimeter-wave imaging techniques and systems have been developed at Pacific Northwest National Laboratory (PNNL) for concealed weapon detection and other applications. These techniques evolved from singlefrequency millimeter-wave holographic imaging methods to wideband three-dimensional planar and cylindrical techniques and systems. The single-frequency holographic method was derived from optical and ultrasonic holography techniques. Speckle is highly significant in this case, and is caused by constructive and destructive interference from multiple scattering locations or depths within a single resolution cell. The wideband three-dimensional techniques developed at PNNL significantly reduce the speckle effect through the use of high depth resolution obtained from the wide bandwidth of the illumination. For these techniques, speckle can still be significant in some cases and affect image quality. In this paper, we explore the situations in which speckle occurs and its relationship to lateral and depth resolution. This will be accomplished through numerical simulation and demonstrated in actual imaging results. Speckle may also play a significant role in altering reflection spectra in wideband terahertz spectra. Reflection from rough surfaces will generate speckle, which will result in significant variation in the reflection spectrum as measured over very wide bandwidths. This effect may make if difficult to interpret spectral absorption features from general reflectance data. In this paper, physical optics numerical simulation techniques will be used to model the reflection from arbitrary random surfaces and explore the effect of the surface on the reflection spectra and reconstructed image. Laboratory imaging and numerical modeling results in the millimeter-wave through the terahertz frequency ranges are presented.
[1]
Thomas E. Hall,et al.
Cylindrical millimeter-wave imaging technique for concealed weapon detection
,
1998,
Other Conferences.
[2]
Jeffrey W. Griffin,et al.
Circularly polarized millimeter-wave imaging for personnel screening
,
2005,
SPIE Defense + Commercial Sensing.
[3]
H. D. Collins,et al.
Concealed explosive detection on personnel using a wideband holographic millimeter-wave imaging system
,
1996,
Defense, Security, and Sensing.
[4]
Thomas E. Hall,et al.
Combined illumination cylindrical millimeter-wave imaging technique for concealed weapon detection
,
2000,
Defense, Security, and Sensing.
[5]
Thomas E. Hall,et al.
Three-dimensional millimeter-wave imaging for concealed weapon detection
,
2001
.
[6]
Mehrdad Soumekh,et al.
A system model and inversion for synthetic aperture radar imaging
,
1990,
International Conference on Acoustics, Speech, and Signal Processing.
[7]
W. R. Tribe,et al.
Security applications of terahertz technology
,
2003,
SPIE Defense + Commercial Sensing.
[8]
Thomas E. Hall,et al.
Cylindrical millimeter-wave imaging technique and applications
,
2006,
SPIE Defense + Commercial Sensing.
[9]
G. D. Crabtree,et al.
A numerical quadrature technique for physical optics scattering analysis
,
1991
.
[10]
G. Bastiaans,et al.
Detection and identification of explosive RDX by THz diffuse reflection spectroscopy.
,
2006,
Optics express.