This PDF file contains the front matter associated with SPIE Proceedings Volume 8544, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Passive submillimeter-wave imaging is a concept that has been in the focus of interest as a promising technology for security applications for a number of years. It utilizes the unique optical properties of submillimeter waves and promises an alternative to millimeter-wave and X-ray backscattering portals for personal security screening in particular. Possible application scenarios demand sensitive, fast, and flexible high-quality imaging techniques. 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. The cameras utilize arrays of superconducting transition-edge sensors (TES), i. e. cryogenic microbolometers, as radiation detectors. The TES are operated at temperatures below 1 K, cooled by a closed-cycle cooling system, and coupled to superconducting readout electronics. By this means, background limited photometry (BLIP) mode is achieved providing the maximum possible signal to noise ratio. At video rates, this leads to a pixel NETD well below 1K. The imaging system is completed by reflector optics based on free-form mirrors. For object distances of 3–10 m, a field of view up to 2m height and a diffraction-limited spatial resolution in the order of 1–2 cm is provided. Opto-mechanical scanning systems are part of the optical setup and capable frame rates up to 25 frames per second. Both spiraliform and linear scanning schemes have been developed. Several electronic and software components are used for system control, signal amplification, and data processing. Our objective is the design of an application-ready and user-friendly imaging system. For application in real world security screening scenarios, it can be extended using image processing and automated threat detection software.

The armed forces are nowadays confronted with a wide variety of types of operations. During peace keeping missions in an urban environment, where small units patrol the streets with armored vehicles, the team leader is confronted with a very complex threat situation. The asymmetric imminence arises in most cases from so called IEDs (Improvised explosive devices) which are found in a multitude of versions. In order to avoid risky situations the early detection of possible threats due to advanced reconnaissance and surveillance sensors will provide an important advantage.

A European consortium consisting of GMV S.A. (Spain, “Grupo Tecnològico e Industrial”), RMA (Belgium, “Royal Military Academy”), TUM (“Technische Universität München”) and DLR (Germany, “Deutsches Zentrum für Luft- und Raumfahrt”) developed in the SUM project (Surveillance in an urban environment using mobile sensors) a low-cost multi-sensor vehicle based surveillance system in order to enhance situational awareness for moving security and military patrols as well as for static checkpoints. The project was funded by the European Defense Agency (EDA) in the Joint Investment Program on Force Protection (JIP-FP).

The SUMIRAD (SUM imaging radiometer) system, developed by DLR, is a fast radiometric imager and part of the SUM sensor suite. This paper will present the principle of the SUMIRAD system and its key components. Furthermore the image processing will be described. Imaging results from several measurement campaigns will be presented. The overall SUM system and the individual subsystems are presented in more detail in separate papers during this conference.

The FP7 Research for SME project IMAGINE - a low cost, high performance monolithic passive mm-wave imager front-end is described in this paper. The main innovation areas for the project are: i) the development of a 94 GHz radiometer chipset and matching circuits suitable for monolithic integration. The chipset consists of a W-band low noise amplifier, fabricated using the commercially available OMMIC D007IH GaAs mHEMT process, and a zero bias resonant interband tunneling diode, fabricated using a patented epi-layer structure that is lattice matched to the same D007IH process; ii) the development of a 94 GHz antenna adapted for low cost manufacturing methods with performance suitable for real-time imaging; iii) the development of a low cost liquid crystal polymer PCB build-up technology with performance suitable for the integration and assembly of a 94 GHz radiometer module; iv) the assembly of technology demonstrator modules. The results achieved in these areas are presented.

This paper discusses the phase effects in the near-field associated with aperture synthesis imaging. The results explain why in some regions of the near-field it is possible to use Fourier transform techniques on a visibility function to create images. However, to generate images deep inside the near-field alternative processing techniques such as the G-matrix method are required. Algorithms based on this technique are used to process imagery from a proof of concept 22 GHz aperture synthesis imager [1]. Techniques for generating synthetic cross-correlations for the aperture synthesis technique are introduced and these are then validated using the image creation algorithms and real data from the proof of concept imager. Using these data the phenomenon of aliasing is explored. The simulation code is then used to illustrate how the effects of aliasing may be minimised by randomising the locations of the antennas over the aperture. The simulation tool is used to show how in the near field the technique can provide a range resolution in 3D imaging of a couple of millimetres when operating with a wavelength of 13 mm. Moving to illustrate the quality of images generated by a next generation aperture synthesis imagers, the software is extended to systems with hundreds of receiver channels.

In the framework of a project [1] dealing with the enforcement of harbor security, a radar based luggage and parcel scanner was developed, with the inherent characteristics of the use of non ionizing radiation and thus without any health hazards for the involved people. The development of hardware and imaging software, based upon near field synthetic aperture algorithms, and fast mechanical scanning is described and first results of high resolution images of threat objects within parcels are shown.

A large 1.6 m aperture mechanically scanning quasi-optical millimetre wave imaging system designed for active use [1] has been investigated for its passive millimetre wave (PMMW) imaging capabilities. This raises new challenges for this imager, as the person / background contrast in indoor security scenarios at these frequencies is in the region of 6-7 K. The system is sensitive over 24 – 28 GHz and has a radiometric sensitivity measured at 6.5 K in a single frame, at a frame rate of 8.8 Hz. It was found that the focal plane receiver array radiated an excess noise ratio (ENR) of typically 9 dB. This radiation re-entered the focal plane array receivers after reflection from the imager optical components typically with a standard deviation of 17 K over the mechanical scan associated with a single image frame. Reflected from subjects in the field of view, it was typically 400 K from a 100 % reflective surface, and 40 K to 100 K from a human subject. This radiation, termed self-emission in this paper, is a feature of many PMMW imaging systems that use highgain electronic amplifiers in their receiving systems. The effectiveness in the use of a calibration mechanism to subtract self-emission reflected from the optical components and a large area quarter wave plate to minimising the amount of self-emission reflected back from subjects is demonstrated. The present system would benefit greatly from replacement amplifiers of larger bandwidth, lower self-emission and lower noise figure. It was also found that the millimetre wave emission from fluorescent room lighting entered the optics of the imager and modulated the received signals at 100 Hz. The mean level of emission was measured at 10 K with a 10 K modulation at 100 Hz for per mode for a 100 % reflecting surface in the room. The best solution to the problem of emission from fluorescent lights was to turn them off and use incandescent lighting.

The recent arrival of TeraHertz large format focal plane arrays has opened the door for numerous applications not previously available for this exciting technology. Video-rate imaging is now a reality and little or no scanning is required. INO has a proven microbolometer based focal plane array that shows good sensitivity over a large THz bandwidth and videos have been successfully acquired of objects hidden behind barrier materials. While these videos successfully proved the real-time capabilities of the INO imager, the quality of the images required substantial system level improvement to be useful for detection and identification purposes in various applications. To this end, INO has designed and fabricated optical components for its active imaging set-up that allows for superior quality real-time images. This paper discusses the concepts and techniques used to create these components. A comparison of images taken using the same THz camera with and without these innovative techniques is presented. In addition, as stand-off detection and imaging is the ultimate objective, an analysis of the atmospheric attenuation over the THz wavelength region is also discussed.

The yttrium-barium-copper oxide cuprate (YBCO) is well-known to exhibit superconducting properties in its YBa₂Cu₃O_(6+x) phase for x close to 1. Oxygen depletion (x ≈ 0.3–0.5) of this compound leads, however, to a semiconductor. An unusual although promising application of YBCO in this semiconducting form can be sought in the field of uncooled thermal detectors of the bolometer type due to its large temperature coefficient of resistance (TCR = 1/R (dR/dT) = –3 to –4 %/K). Besides, semiconducting YBCO films can be deposited without substrate heating in amorphous semiconducting form (a-YBCO), which makes the integration of this material compatible with already processed signal readout electronics (e.g. a CMOS chip). In the present work, we consider two a-YBCO bolometric geometries, i.e. planar (#Si-pla) or trilayer (#Si-tri), and compare their detection performance with reference to already reported semiconducting devices, mainly designed for room temperature operation. For both detector devices, the response was measured at 850 nm wavelength for experimental convenience. The response of device #Si-pla exhibited a low-frequency regular low-pass bolometric behavior (30 Hz cut-off), followed by a high-pass behavior (60 kHz cut-off / 3 μs time constant) that could be assigned to the pyroelectric state of a-YBCO. The response of device #Si-tri exhibited the high-pass behavior only. Detectivity values up to 3.5×10⁸ cm⋅Hz^1/2⋅W⁻¹ have been measured. The high frequency sensitivity offers a promising solution for fast imaging applications, especially in the far IR / THz range where moderate cost systems should be considered.

Satellite Low Noise Block-down convertors (LNBs) have been evaluated for use in amplitude and intensity interferometry. LNBs have been found to have a high performance to cost ratio which is beneficial for any sensor system. They are investigated here for a diversity of applications from the derisking of subsystems for next generation aperture synthesis imagers having hundreds of channels [1] to a platform for the investigation of phase recovery in intensity interferometry and experimentation in entangled photons. Measured noise temperatures of LNBs were found to lie between 170 K and 300 K which is higher than typical manufacturers’ specifications. A twin channel interferometer system was developed using satellite receiver feeds and LNBs at the front-end, other amplifiers, mixers, filters and local oscillators at intermediate stages, and 8-bit USB ADCs sampling synchronously at 100 MHz and a PC for data processing. LabVIEW was used to digitally demodulate the sampled data and process it into the first and second orders of coherence. Measurements of the first order of coherence from a standard low energy discharge lamp indicated interference fringes were commensurate with range and spacing of the two receivers and the source. The relationship between the measured first and second order of coherence agrees within the experimental error. Variations of the first and second orders of coherence with range, R, follow the relationship 1/R and 1/R2. The system has the potential for investigations into phase extraction for intensity interferometry and for the study of digital demodulation schemes for aperture synthesis amplitude interferometry with hundreds of receiver channels for next generation security screening systems. A twin, triple or quadruple channel polarimetric LNB interferometer could be used as basis for high precision investigations in to entangled photons and quantum communications.

Fusion of multispectral images has been explored for many years for security and used in a number of commercial products. CEA-Leti and FBK have developed an innovative sensor technology that gathers monolithically on a unique focal plane arrays, pixels sensitive to radiation in three spectral ranges that are terahertz (THz), infrared (IR) and visible. This technology benefits of many assets for volume market: compactness, full CMOS compatibility on 200mm wafers, advanced functions of the CMOS read-out integrated circuit (ROIC), and operation at room temperature. The ROIC houses visible APS diodes while IR and THz detections are carried out by microbolometers collectively processed above the CMOS substrate. Standard IR bolometric microbridges (160x160 pixels) are surrounding antenna-coupled bolometers (32X32 pixels) built on a resonant cavity customized to THz sensing. This paper presents the different technological challenges achieved in this development and first electrical and sensitivity experimental tests.

The objective of this work was to create a low cost sensor array that operates at room temperature for millimeter wave applications and could be used for FM radars and various heterodyne receivers. The selected technology was silicon wafer micromachining allowing the creation of microstructures on silicon membranes using different metal layers. The technology used allowed submicron dimensions for a photolithography pattern and thin membranes down to a few micrometers. One of the most critical requirements for the sensor was to achieve a high signal-to-noise ratio and a high bandwidth for a mixed frequency. The sensor is a titanium-based micro-bolometer connected to the micro-antenna which is integrated with the bolometer. The results are very promising. The measured NEP is below 5pW/√Hz and the sensitivity is close to 1000 V/W. In the paper the antenna - bolometer sensor microstructure is analyzed. Theoretical analysis and design guidelines for the bolometer itself are discussed. Simulation results of the bolometer and antenna show very close matching to the measured results. Characterization measurements were performed, and thermal behavior of microbolometer structure was simulated and measured. The measurement results are presented for THz FM radar different targets, and a technology demonstrator is also described.

This paper describes how an open source 3D computer modeling, animation and visualization software package was modified to simulate the millimeter-wave imaging process. The data that describes the scene is specified with a network of interconnected planar triangular polygons. Each polygon is assigned a material type that defines a number of attributes such as thickness, and temperature, the material can also define the optical properties using refractive index or reflectivity, transmission and emissivity. The Bidirectional Reflectance Distribution Function (BRDF) can also be used for reflection from rough surfaces. The scene, which may contain human figures can be animated to show movement. The paper describes the key elements of the radiometric model and how a post processing technique allows a range of different types of imagers to be simulated with noise and depth of field. The paper concludes with some examples and a discussion of how accurate such a modeling approach can be.

The European Defence Agency (EDA) engages countermeasures against Improvised Explosive Devices (IEDs) by funding several scientific programs on threat awareness, countermeasures IEDs or land-mine detection, in which this work is only one of numerous projects. The program, denoted as Surveillance in an urban environment using mobile sensors (SUM), covers the idea of equipping one or more vehicles of a patrol or a convoy with a set of sensors exploiting different physical principles in order to gain detailed insights of the road situation ahead. In order to give an added value to a conventional visual camera system, measurement data from an infra-red (IR) camera, a radiometer and a millimetre-wave radar are fused with data from an optical image and are displayed on a human-machine-interface (HMI) which shall assist the vehicle’s co-driver to identify suspect objects or persons on or next to the road without forcing the vehicle to stop its cruise. This paper shall especially cover the role of the millimetre-wave radar sensor and its different operational modes. Measurement results are discussed. It is possible to alter the antenna mechanically which gives two choices for a field of view and angular resolution trade-off. Furthermore a synthetic aperture radar mode is possible and has been tested successfully. MIMO radar principles like orthogonal signal design were exploited tofrom a virtual array by 4 transmitters and 4 receivers. In joint evaluation, it was possible to detect e.g. grenade shells under cardboard boxes or covered metal barrels which were invisible for optical or infra-red detection.

We demonstrate real-time computer code improving significantly the quality of images captured by the passive THz imaging system. The code is not only designed for a THz passive device: it can be applied to any kind of such devices and active THz imaging systems as well. We applied our code for computer processing of images captured by various passive THz imaging devices manufactured by different companies. The performance of current version of the computer code is greater than one image per second for a THz image having more than 5000 pixels and 24 bit number representation. Processing of THz single image produces about 20 images simultaneously corresponding to various spatial filters. The computer code allows increasing the number of pixels for processed images without noticeable reduction of image quality. The performance of the computer code can be increased many times using parallel algorithms for processing the image. We develop original spatial filters which allow one to see objects with sizes less than 2 cm. The digital imagery is produced by passive THz imaging devices which captured the images of objects hidden under opaque clothes. For images with high noise we develop an approach which results in suppression of the noise after using the computer processing and we obtain the good quality image. The results demonstrate the high efficiency of our approach for the detection of hidden objects and they are a very promising solution for the security problem.

An FM-CW radar at 94 GHz has been equipped with antennas with high azimuthal gain and a broad beam in elevation and mounted on a rotating pedestal. The radar covers a range interval of 500 m. A change detection algorithm is used to discriminate invading persons from the background. Tracking of non-stationary target objects is maintained by Kalman filtering. The RCS of detected objects is determined using a pre-calibration against a precision corner reflector at a defined range. The measured RCS is compared with a threshold value to discriminate between dangerous and nondangerous persons. Additional information from a video camera is necessary for a first discrimination between target classes.

Detection of nanosecond pulses by fast and sensitive Hot Electron Bolometer (HEB) is reported. Pulses were generated by an Optical Parametric Oscillator (OPO)-based source. The laser can be tuned in the range 0.7-2.5 THz; its repetition rate equals to 53Hz, duration of the pulse is about 10-20ns, energy is 10nJ and spectral width 50GHz. HEB operates at temperature of about 8.8K in a cryogenic refrigeration system. A sensitive element is a bridge from a 4-mm thick NbN film integrated with a planar logarithmic spiral antenna on a high-resistive silicon. HEB works in 0.3-3THz range with NEP ~3x10^-13 W/Hz^1/2 and dynamic range 0.1 uW. Thanks to exploitation of hot electrons in superconducting state, the detector is very fast with minimum response time equals to 50ps. The THz radiation is focused with a silicon lens, and then is coupled to a sensitive bolometer using the planar antenna. THz radiation from the OPO, through a set of mirrors and attenuators, was coupled to the detector. The distance between the source and detector was about 3m. Full Width at Half Maximum of the recorded pulses was about 20 ns. Moreover, we measured linearity of the detector in the range 0.7- 2.0 THz by rotation of the polarizer axis. The pulses were averaged and integrated for better stability. We obtained a good similarity to the theoretical curve of the polarizer.

Terahertz technology is one of emerging technologies that has a potential to change our life. There are a lot of attractive applications in fields like security, astronomy, biology and medicine. Until recent years, terahertz (THz) waves were an undiscovered, or most importantly, an unexploited area of electromagnetic spectrum. The reasons of this fact were difficulties in generation and detection of THz waves. Recent advances in hardware technology have started to open up the field to new applications such as THz imaging. The THz waves can penetrate through various materials. However, automated processing of THz images can be challenging. The THz frequency band is specially suited for clothes penetration because this radiation does not point any harmful ionizing effects thus it is safe for human beings. Strong technology development in this band have sparked with few interesting devices. Even if the development of THz cameras is an emerging topic, commercially available passive cameras still offer images of poor quality mainly because of its low resolution and low detectors sensitivity. Therefore, THz image processing is very challenging and urgent topic. Digital THz image processing is a really promising and cost-effective way for demanding security and defense applications. In the article we demonstrate the results of image quality enhancement and image fusion of images captured by a commercially available passive THz camera by means of various combined methods. Our research is focused on dangerous objects detection - guns, knives and bombs hidden under some popular types of clothing.