Terahertz- (THz) and millimeter-wave sensors are becoming more important in industrial, security, medical, and defense applications. A major problem in these sensing areas is the resolution, sensitivity, and visual acuity of the imaging systems. There are different fundamental parameters in designing a system that have significant effects on the imaging performance. The performance of THz systems can be discussed in terms of two characteristics: sensitivity and spatial resolution. New approaches for design and manufacturing of THz imagers are a vital basis for developing future applications. Photonics solutions have been at the technological forefront in THz band applications. A single scan antenna does not provide reasonable resolution, sensitivity, and speed. An effective approach to imaging is placing a high-performance antenna in a two-dimensional antenna array to achieve higher radiation efficiency and higher resolution in the imaging systems. Here, we present the performance modeling of a pupil plane imaging system to find the resolution and sensitivity efficiency of the imaging system.
Proc. SPIE. 10625, Infrared Imaging Systems: Design, Analysis, Modeling, and Testing XXIX
KEYWORDS: Target detection, Infrared search and track, Staring arrays, Long wavelength infrared, Signal to noise ratio, Unmanned aerial vehicles, Point spread functions, Sensors, Black bodies, Infrared radiation
Unmanned aerial vehicles (UAVs) have become more readily available in the past 5 years and are proliferating rapidly. New aviation regulations are accelerating the use of UAVs in many applications. As a result, there are increasing concerns of potential air threats in situational environments including commercial airport security and drug trafficking. In this study, radiometric signatures of commercially available miniature UAVs is determined for long-wave infrared (LWIR) bands in both clear sky and partial cloudy conditions. Results are presented that compare LWIR performance estimates for the detection of commercial UAVs via infrared search and track (IRST) systems with two candidate sensors.
The spectral response of cameras is often reported as the product of the individual responses of the elements in the optical path, the lens element coatings, filter (if available), FPA window and coating, and detector elements. This data is often incomplete or inaccurate as vendors will often provide limited spectral data or the data is measured under conditions different than those in the camera system (i.e., normal incidence assumption). We have designed and built an instrument for the measurement of the normalized spectral response of camera systems in the thermal bands (MWIR [3um-6um] and LWIR [8um – 12um]). The design utilizes a series of narrowband filters, a cavity blackbody and other components for the conditioning of the stimuli to the camera. The normalized camera spectral response is obtained by comparing the camera response to each narrowband filter against a reference measurement. In this paper we discuss the modeling and analysis in support of the design, show the final design and some preliminary measurements.
Panoramic imaging is inherently wide field of view. High sensitivity uncooled Long Wave Infrared (LWIR) imaging requires low F-number optics. These two requirements result in short back working distance designs that, in addition to being costly, are challenging to integrate with commercially available uncooled LWIR cameras and cores. Common challenges include the relocation of the shutter flag, custom calibration of the camera dynamic range and NUC tables, focusing, and athermalization. Solutions to these challenges add to the system cost and make panoramic uncooled LWIR cameras commercially unattractive. In this paper, we present the design of Panoramic Imaging Relay Optics (PIRO) and show imagery and test results with one of the first prototypes. PIRO designs use several reflective surfaces (generally two) to relay a panoramic scene onto a real, donut-shaped image. The PIRO donut is imaged on the focal plane of the camera using a commercially-off-the-shelf (COTS) low F-number lens. This approach results in low component cost and effortless integration with pre-calibrated commercially available cameras and lenses.
As the defense budget reduces and we are asked to do more with less (seems to have been a major theme
now for over 10 years), multifunction systems are becoming critical to the future of military EOIR systems.
The design of multifunction (MF) sensors is not a well-developed or well-understood discipline. In this
paper, we provide an example trade study of a ground combat system hyperhemispheric multifunction
system. In addition, we show how concept evaluation can be achieved using a virtual prototyping
Panoramic infrared imaging is relatively new and has many applications to include tower mounted security systems, shipboard protection, and platform situational awareness. In this paper, we review metrics and methods that can be used for analysis of requirements for an infrared panoramic imaging system for military vehicles. We begin with a broad view of general military requirements organized into three categories, survivability, mobility, and lethality. A few requirements for the sensor modes of operation across all categories are selected so that panoramic system design can address as many needs as possible, but with affordability applied to system design. Metrics and associated methods that can translate military operational requirements into panoramic imager requirements are discussed in detail in this paper.
As pixels have gotten smaller and focal plane array sizes larger, it may be practical to make EO-IR systems which are inherently multifunctional. A system intended to perform threat warning, pilotage imaging and target acquisition imaging would be a multifunctional system. This notional system could be panoramic or hemispheric, with cameras covering all of space simultaneously. It could save cost and weight over federated systems. However, can all of these disparate tasks be performed successfully by a single system, or will the trade-offs compromise the potential savings? Targeting sensors have typically been designed to create long range, high resolution imagery for detection and identification. The imagery is optimized to suppress the scene/clutter and maximize the target signature. Pilotage sensors have typically been wide field of view, unity magnification systems which maximize scene contrast to enable safe flight. Threat warning sensors are intended to detect non or under resolved (spatially or temporally) targets/events using algorithms, and to discriminate them from clutter or solar glint. The first two applications involve imagery for human operator consumption, while the third feeds algorithms. With these disparate performance goals, there is a wide variety of competing metrics used to optimize these sensors -- F/no, FOV/IFOV, frame rate, NETD, NEI, FAR, Probability of Identification, etc. This study is a look at how these performance parameters and system descriptors trade and their relative impacts.
Panoramic imagers are becoming more commonplace in the visible part of the spectrum. These imagers are often used in the real estate market, extreme sports, teleconferencing, and security applications. Infrared panoramic imagers, on the other hand, are not as common and only a few have been demonstrated. A panoramic image can be formed in several ways, using pan and stitch, distributed aperture, or omnidirectional optics. When omnidirectional optics are used, the detected image is a warped view of the world that is mapped on the focal plane array in a donut shape. The final image on the display is the mapping of the omnidirectional donut shape image back to the panoramic world view. In this paper we analyze the performance of uncooled thermal panoramic imagers that use omnidirectional optics, focusing on range performance.
In the absence of detector arrays, a single pixel coupled with an image plane coded aperture has been shown to be a practical solution to imaging problems in the terahertz and sub-millimeter wave domains. The authors demonstrate two laboratory, real-time, two-dimensional, sub-millimeter wave imagers that are based on an image plane coded aperture. These active imaging systems consist of a heterodyne source and receiver pair, image forming optics, a coded aperture, data acquisition hardware, and image reconstruction software. In one of the configurations, the target is measured in transmission, while in the other it is measured in reflection. In both configurations, images of the targets are formed on the coded aperture, and linear measurements of the image are acquired as the aperture patterns change. Once a sufficient number of linearly independent measurements are obtained, the image is reconstructed by solving a system of linear equations that is generated from the aperture patterns and the corresponding measurements. The authors show that for image sizes envisioned for many current applications, this image reconstruction technique is computationally efficient and can be implemented in real time. Measurements are collected with these systems, and the reconstruction results are presented and discussed.
There is a need to model complementary aspects of various data channels in distributed sensor networks in order to
provide efficient tools of decision support in rapidly changing, dynamic real life scenarios. Our aim is to develop an
autonomous cyber-sensing system that supports decision support based on the integration of information from diverse
sensory channels. Target scenarios include dismounts performing various peaceful and/or potentially malicious
activities. The studied test bed includes K<sub>u</sub> band high bandwidth radar for high resolution range data and K band low
bandwidth radar for high Doppler resolution data. We embed the physical sensor network in cyber network domain to
achieve robust and resilient operation in adversary conditions. We demonstrate the operation of the integrated sensor
system using artificial neural networks for the classification of human activities.
Various schemes for active imaging require different allocations of source power and can result in different overall
signal to noise ratios. At the University of Memphis we have developed an image-plane scanning device used
with a single pixel detector to form video rate images of the scene. Imaging with this device requires flood
illumination of the scene. Because sub-millimeter wave sources typically produce low power, it is a common
belief that flood illumination results in low detected signal power and therefore low signal to noise ratios (SNR)
at the detector. In this work we quantify the SNR at the detector for our system and compare it to conventional
imaging systems, conjugate point imaging systems, and focal plane array imaging. Unlike the other two systems,
imaging with our device requires an additional pixel formation step; therefore, the SNR at the detector is not
the per-pixel SNR. We present the limits of the per-pixel SNR and discuss its dependence on various device
Laser Induced Breakdown Spectroscopy (LIBS) utilizes a diversity of standard spectroscopic techniques for
classification of materials present in the sample. Pre-excitation processing sometimes limits the analyte to a short list of
candidates. Prior art demonstrates that sparsity is present in the data. This is sometimes characterized as identification
by components. Traditionally, spectroscopic identification has been accomplished by an expert reader in a manner
typical for MRI images in the medicine. In an effort to automate this process, more recent art has emphasized the use of
customized variations to standard classification algorithms. In addition, formal mathematical proofs for compressive
sensing have been advanced. Recently the University of Memphis has been contracted by the Spectroscopic Materials
Identification Center to advance and characterize the sensor research and development related to LIBS. Applications
include portable standoff sensing for improvised explosive device detection and related law enforcement and military
applications. Reduction of the mass, power consumption and other portability parameters is seen as dependent on
classification choices for a LIBS system. This paper presents results for the comparison of standard LIBS classification
techniques to those implied by Compressive Sensing mathematics. Optimization results and implications for portable
LIBS design are presented.
Proc. SPIE. 8022, Passive Millimeter-Wave Imaging Technology XIV
KEYWORDS: Staring arrays, Extremely high frequency, Millimeter wave imaging, Imaging systems, Receivers, Imaging devices, Data acquisition, Simulation of CCA and DLA aggregates, Current controlled current source, Compressed sensing
In this paper we demonstrate the use of compressive sensing to form an image with an image plane random
mask and a single pixel sub-millimeter wave receiver. This type of imaging device is a practical solution in
domains where focal plane arrays do not exist. The imager consists of a heterodyne source and receiver pair,
image forming optics, a spatially selective mask, and data acquisition and post-processing hardware and software.
The spatially selective mask modulates the signal measured by the receiver which is then sampled by an analog
to digital converter and is post-processed to reconstruct the image. The spatially selective mask can produce
image samples at full video rates. The post-processing used for this research consists of a sparseness inducing
transformation on the measurements and application of compressive sensing reconstruction algorithms. We show
several images acquired and reconstructed using this system. While the data acquisition of this system is real
time, the processing currently must be done online. We comment on the performance improvement by using compressive sensing methods.
In the absence of detector arrays, a single pixel coupled with a spatially selective mask has been shown to
be a practical solution to imaging problems in the terahertz and sub-millimeter wave domains. In this paper
we demonstrate real-time two-dimensional imager for sub-millimeter waves that is based on a spatially selective
image plane mask. The imager consists of a heterodyne source and receiver pair, image forming optics, a spatially
selective mask, data acquisition hardware, and image reconstruction software. The optics form an image onto
the spatially selective mask and linear measurements of the image are made. The mask must be designed
to ensure maximum transmission, measurement linearity, and measurement to measurement independence and
our design parameters are presented. Once enough linearly independent measurements are made, the image
is reconstructed by solving a system of linear equations that is generated from the mask patterns and the
corresponding measurements. We show that for image sizes envisioned for many current applications, this image
reconstruction technique is computationally efficient and can be implemented in real time. We present images
collected using this system, discuss the results, and discuss other applications for some components of the imager.
In this paper, the design and implementation of a sub-millimeter line scanning imager using a novel imageforming
device is described. The system consists of a coherent illuminator, an optical system, an image plane
mask, and a coherent detector. The image plane mask is formed by making a sequence of holes along a constant
radius of a metal disk. Spinning the disk scans the holes through the image formed on it. A detector placed
behind the spinning disk collects radiation passing through the holes. The holes are arranged in a pseudorandom
pattern. At each detector sample time, energy from a different pattern of holes is collected. A rigorous
electromagnetic analysis shows that, for a certain minimum size and spacing of holes and certain disk thicknesses,
these measurements constitute a linear measurement of the energy in the image formed on the disk. Using
techniques reminiscent of those used in compressive sensing, the image is then reconstructed by applying an
inverse linear matrix transform to these measurements. We show how simulation can be used to optimize the
design of the disk. We demonstrate a laboratory version of this device and discuss future efforts to systematize
it. Extensions to full two-dimensional imaging are also discussed.
In this paper we present a single mode active device for sub-millimeter wave line imaging. The illuminated scene
is imaged through focusing optics onto a device we have developed and have dubbed a spatially selective mask
(SSM). This device transmits parts of the image onto a heterodyne receiver. Currently the SSM is capable of
transmitting user-selectable parts of one line of the image that is focused on it. Multiple patterns are used to
sample a line in the image. The voltage in the receiver resulting from each pattern constitutes an independent
measurement of the illuminated scene along a line. A one dimensional image is reconstructed from the measurement
results and a priori knowledge of the patterns using methods derived from the theory of compressive
sensing. The theory behind the device and the design principles we use are reviewed. We show line images
obtained at 640 GHz. Extension of this technique to two dimensional imaging is discussed.
In this paper a two dimensional electromagnetic analysis and numerical simulations for a structure consisting of a
resistive sheet backed by a spatially non-uniform perfectly conducting reflector is presented. The analyzed nonuniformity
is a dip or bump on the reflector surface. The analysis is aimed at the design and evaluation of this structure
as a spatially selective mirror for use in a single pixel sub-millimeter wave imager. Scattered and absorbed powers as
well as the scattered radiation intensity are calculated in the far field for illumination by a linearly polarized, tapered
Gaussian beam. Simulations for normally incident radiation and radiation at obtuse angles are presented. The scattered
field in the far region is measured (simulation) by a receiving antenna and the dependence of the simulated received
power on the position of the non-uniformity is observed. The dependence of the simulated received power on the size of
the non-uniformity on the reflector is also presented. We conclude with the description of a single pixel sub-millimeter
wave imager that uses the analyzed structure.
This paper describes the modeling of human task performance using a passive interferometric millimeter
wave (MMW) imaging sensor. The model is based on a previous model developed for concealed weapon
identification using an active terahertz imager. Both models leverage the task performance modeling
approach developed by the US Army Night Vision and Electronic Sensors Directorate. Key developments
for this model include modeling of the effects of an interferometric antenna array, including sparse arrays,
and a novel optical upconversion and processing stage being developed by the University of Delaware.
Sparse interferometric arrays do not fully sample the spatial frequency extent of the image and as a result,
can have degraded spatial frequency response over a fully populated array. The spatial frequency response
of the sparse array can have a dramatic effect on image quality. Image quality is empirically related to task
performance through the use of perception experiments. Possible applications of this model include system
trade studies, concealed weapon identification, and navigation in fog and brown out conditions.
Terahertz imaging currently is done using single pixel imagers mechanically scanned over the field of view. Focal
planes will reduce the need for mechanical scanning but are still under development. In the 70s, Jacobs , et. al.,
proposed and demonstrated a device for millimeter wave imaging using a single pixel. The device obviated the need for
large mechanical scanning mechanisms by using an optically scanned bulk semiconductor in a resonant structure. In this
research, a device of this type is analyzed for suitability as an element in a terahertz or sub-millimeter wave imager. The
device is simulated under simultaneous illumination from a coherent RF source and a coherent optical source (a laser).
A computational electromagnetic model of the device is described. Device and system performance metrics are defined
and predicted performance presented. Finally design of a system incorporating this device is discussed.