In recent years, body scanner technologies based on millimeter-wave and terahertz technologies have been shown to improve security in areas sensitive to terrorist attacks by detecting hazardous objects hidden underneath the clothing of people. Inevitably, useful devices have to provide an adequate compromise between spatial resolution limited due to diffraction and penetration through clothing. Within this context, the spectral absorption of a wide range of fabric, interference caused by the texture, and the effect of moisture within the fabric have to be considered. We have studied these effects by time-domain and Fourier transformation spectroscopy. The experimental findings are verified using a passive THz security camera operating in two frequency bands at 0.85 and 0.35 THz. The latter band was proven to be of superior use for security checks as it provides useful results even in cases of wet clothes.

Passive submillimeter-wave imaging is a concept that has been in the focus of interest as a promising technology for personal security screening for a number of years. In contradiction to established portal-based millimeter-wave scanning techniques, it allows for scanning people from a distance in real time with high throughput and without a distinct inspection procedure. This opens up new possibilities for scanning, which directly address an urgent security need of modern societies: protecting crowds and critical infrastructure from the growing threat of individual terror attacks. Considering the low radiometric contrast of indoor scenes in the submillimeter range, this objective calls for an extremely high detector sensitivity that can only be achieved using cooled detectors. Our approach to this task is a series of passive standoff video cameras for the 350 GHz band that represent an evolving concept and a continuous development since 2007. Arrays of superconducting transition-edge sensors (TES), operated at temperatures below 1 K, are used as radiation detectors. By this means, background limited performance (BLIP) mode is achieved, providing the maximum possible signal to noise ratio. At video rates, this leads to a temperature resolution well below 1 K. The imaging system is completed by reflector optics based on freeform mirrors. For object distances of 5-25 m, a field of view up to 2 m height and J Infrared Milli Terahz Waves a diffraction-limited spatial resolution in the order of 1-2 cm is provided. Optomechanical scanning systems are part of the optical setup and capable of frame rates of up to 25 frames per second.

We present the concept and experimental set-up of a passive submillimeter-wave stand-off imaging system for security applications. Our ambition is the design of an application-ready and user-friendly camera providing high sensitivity and high spatial resolution at video frame rates. As an intermediate step towards this goal, the current prototype already achieves a frame rate of 10 frames per second and a spatial resolution below 2 cm at 8 m distance. The camera is the result of a continuous development and a unique concept that yielded first high-resolution passive submillimeter-wave images provided by cryogenic sensors in May et al. (2007). It is based on an array of 20 superconducting transition-edge sensors operated at a temperature of 450 mK, a closed-cycle cooling system, a Cassegrain-type optics with a 50 cm main mirror, and an opto-mechanical scanner. Its outstanding features are the scanning solution allowing for high frame rates and the compact and integrated system design.

Downloaded From: http://opticalengineering.spiedigitallibrary.org/ on 05/15/2015 Terms of Use: http://spiedl.org/termsAbstract. Against a background of newly emerged security threats, the well-established idea of utilizing submillimeter-wave radiation for personal security screening applications has recently evolved into a promising technology. Possible application scenarios demand sensitive, fast, flexible and high-quality imaging techniques. At present, best results are obtained by passive imaging using cryogenic microbolometers as radiation detectors. Building upon the concept of a passive submillimeter-wave stand-off video camera introduced previously, we present the evolution of this concept into a practical application-ready imaging device. This has been achieved using a variety of measures such as optimizing the detector parameters, improving the scanning mechanism, increasing the sampling speed, and enhancing the image generation software. The camera concept is based on a Cassegrain-type mirror optics, an optomechanical scanner, an array of 20 superconducting transition-edge sensors operated at a temperature of 450 to 650 mK, and a closed-cycle cryogen-free cooling system. The main figures of the system include: a frequency band of 350 ± 40 GHz, an object distance of 7 to 10 m, a circular field of view of 1.05 m diameter, and a spatial resolution in the image center of 2 cm at 8.5 m distance, a noise equivalent temperature difference of 0.1 to 0.4 K, and a maximum frame rate of 10 Hz. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).

Kinematic laser scanning is widely used for the fast and accurate acquisition of road corridors. In this context, road monitoring is a crucial application, since deficiencies of the road surface due to non-planarity and subsidence put traffic at risk. In recent years, a Mobile Mapping System (MMS) has been developed at the University of Bonn, consisting of a GNSS/IMU unit and a 2D laser scanner. The goal of this paper is to evaluate the accuracy and precision of this MMS, where the height component is of main interest. Following this, the applicability of the MMS for monitoring the planarity and subsidence of road surfaces is analyzed. The test area for this study is a 6 km long section of the A44n motorway in Germany. For the evaluation of the MMS, leveled control points along the motorway as well as point cloud comparisons of repeated passes were used. In order to transform the ellipsoidal heights of the MMS into the physical height system of the control points, undulations were utilized. In this respect, a local tilt correction for the geoid model was determined based on GNSS baselines and leveling, leading to a physical height accuracy of the MMS of < 10 mm (RMS). The related height precision has a standard deviation of about 5 mm. Hence, a potential subsidence of the road surface in the order of a few cm is detectable. In addition, the point clouds were used to analyze the planarity of the road surface. In the course of this, the cross fall of the road was estimated with a standard deviation of < 0.07 %. Yet, no deficiencies of the road surface in the form of significant rut depths or fictive water depths were detected, indicating the proper condition of the A44n motorway. According to our tests, the MMS is appropriate for road monitoring.