Search

Introduction to SPIE Defense and Commercial Sensing conference 11745: Passive and Active Millimeter-Wave Imaging XXIV

A dual-DDS-based, mm-wave, heterodyne, FMCW radar with a 108-GHz center frequency, a 600-MHz bandwidth, and a 3-MHz IF was used to characterize backscatter from static clutter and a small, fast-moving target. Employing a symmetric triangular frequency-vs-time FMCW waveform with 500-us up-chirp and down-chirp durations, signals from a reusable paintball (reball) with a radial velocity of about 90 m/s were measured in an indoor, clutter-rich environment over intervals of ∼100-ms. Unambiguous estimation of the reball's range and radial velocity were derived from observations made during both the up-chirp and down-chirp observations. Specifically, when the reball's echo signal was obscured or degraded by coincident clutter (e.g. during down-chirp), estimates of its amplitude characteristics were obtained from measurements when the reball and clutter were spectrally separable (during up-chirp). Consequently, it is demonstrated that the clutter in this context can be suppressed by more than 25 dB.

This paper presents calibrated radar cross section (RCS) data of various objects considered to be a hazard for a landing helicopter and a technique for extracting these values from inverse synthetic aperture radar (ISAR) imagery. Data was collected at an outdoor facility using a fully polarimetric, 94-GHz radar mounted on an elevator that was positioned on a 125-foot tower to collect data at various depression angles. Targets were placed on a 22-foot diameter turntable and rotated a full 360 degrees to form ISAR imagery at all aspect angles. The technique being described was formulated to enable the extraction of objects of interest from the imagery. In order to calculate accurate RCS data of each object on the turntable, an area within the ISAR image was assigned to each object for every image formed during a full rotation. This area was tracked as it traveled 360 degrees enabling the generation of polar plots of RCS. This was done at multiple depression angles to capture the linear co- and cross-polarized signatures. The measured objects include a large metal cube, a chain link fence and a 1.5-in. diameter wound-metal cable.

Stretch processing is widely used as a means to pulse compress the echoes produced by wideband LFM waveforms at a lower sampling bandwidth while still preserving high range resolution. Here the final fast Fourier transform (FFT) stage is replaced by a compensation transform that permits the use of other chirp-like nonlinear FM (NLFM) waveforms without changing the rest of the RF receive chain, thereby facilitating greater diversity in the use of wideband waveforms for legacy radar systems. The efficacy of this approach is experimentally demonstrated using open-air measurements.

Traditional stretch processing performs match filtering using a Fourier transform, which is essentially the matched filter bank for an LFM waveform mixed with an LFM reference. Here we consider how optimal least-squares based mismatched filtering could be used in place of the Fourier transform. This notion is then taken a step further with the formulation of an adaptive transformation. These new stretch processing filter structures are demonstrated in simulation and experimentally using open-air measurements, with the enhancements they enable applicable to a wide variety of legacy systems.

We investigate how realistic architecture considerations affect the performance of wafer-scale electronically scanned millimeter-wave reflectarrays. Considering the application of a confocal Gregorian optics geometry with a small angular field of view, we examine how a reflectarray's discrete (digital) phase state quantization and electrical size impact scan angle accuracy and quantization lobe performance degradation. We quantify the impact of these effects on the camera's imaging performance and show that, for these reflectarrays, phase quantization of 2 bits is sufficient.

A new method for synthesizing broadband antireflective (AR) surfaces at microwave and millimeter wave frequencies is demonstrated. The AR surface, we call an inverse motheye, was formed by machining a multi-layer grating of subwavelength circular holes into a non-absorptive dielectric. This created low reflected energies (

A method for synthesizing broadband antireflective (AR) surfaces at millimeter wave frequencies is demonstrated. AR surfaces were formed by machining a multilayer subwavelength structures into nonabsorptive dielectrics. This created low-reflected energies (

We describe a computational imaging technique to extend the depth-of-field of a 94-GHz imaging system. The technique uses a cubic phase element in the pupil plane of the system to render system operation relatively insensitive to object distance. However, the cubic phase element also introduces aberrations but, since these are fixed and known, we remove them using post-detection signal processing. We present experimental results that validate system performance and indicate a greater than four-fold increase in depth-of-field from 17rdquo to greater than 68rdquo.

Summary and analysis of 216 GHz polarimetric measurements of LQ situ rain Abigail S. Hedden 1 *, David A. Wikner 1 , Russell W. Bradley 1,2 1 U.S. Army Research Laboratory, 2800 Powder Mill Rd., Adelphi, MD 20783 2 Virginia Tech University, Blacksburg, VA 24061 ABSTRACT The Army Research Laboratory (ARL) has developed a polarimetric frequency-modulated continuous-wave (FMCW) instrumentation radar that has been used to study the polarization and backscatter properties of in-situ rain in the 220 GHz atmospheric window. A summary of the preliminary measurements is presented in this work including an analysis of the co -polarization backscatter and attenuation characteristics measured at 216 GHz . A marginal detection of the co-polarization backscatter signature of rain was made during a series of fast-moving, heavy downpour thunderstorm events . A detection limit of - 40 ±3 dB[m 2 /m 3 ] was found for the VV-polarization cross section per unit volume for rain rates up to 150 mm/hr. Co-polarization (VV- and HH-polarization) attenuation characteristics measured at high rain rates (> 20 mm/hr) were well described by a Joss thunderstorm drop distribution in the high frequency limit, where drop size is much greater than the observation wavelength. Observations at 216 GHz suggest attenuation levels of 8- 10 dB/km at rain rates above 20 mm/hr, strengthening previous evidence that attenuation through rain is independent of frequency under high rain rate conditions. Attenuation measurements at lower rain rates (< 20 mm/hr) were qualitatively consistent with both Laws and Parsons and Joss thunderstorm distributions. Keywords: millimeter wave propagation, backscatter, rain, millimeter wave radar, radar polarimetry

The development of sensors that are capable of penetrating smoke, dust, fog, clouds, and rain is critical for maintaining situational awareness in degraded visual environments and for providing support to the Warfighter. Atmospheric penetration properties, the ability to form high-resolution imagery with modest apertures, and available source power make the extremely high-frequency (EHF) portion of the spectrum promising for the development of radio frequency (RF) sensors capable of penetrating visual obscurants. Comprehensive phenomenology studies including polarization and backscatter properties of relevant targets are lacking at these frequencies. The Army Research Laboratory (ARL) is developing a fully-polarimetric frequency-modulated continuous-wave (FMCW) instrumentation radar to explore polarization and backscatter properties of in-situ rain, scattering from natural and man-made surfaces, and the radar cross section and micro-Doppler signatures of humans at EHF frequencies, specifically, around the 220 GHz atmospheric window. This work presents an overview of the design and construction of the radar system, hardware performance, data acquisition software, and initial results including an analysis of human micro-Doppler signatures.

Providing situational awareness to the warfighter requires radar, communications, and other electronic systems that operate in increasingly cluttered and dynamic electromagnetic environments. There is a growing need for cognitive RF systems that are capable of monitoring, adapting to, and learning from their environments in order to maintain their effectiveness and functionality. Additionally, radar systems are needed that are capable of adapting to an increased number of targets of interest. Cognitive nonlinear radar may offer critical solutions to these growing problems. This work focuses on ongoing efforts at the U.S. Army Research Laboratory (ARL) to develop a cognitive nonlinear radar test-bed. ARL is working toward developing a test-bed that uses spectrum sensing to monitor the RF environment and dynamically change the transmit waveforms to achieve detection of nonlinear targets with high confidence. This work presents the architecture of the test-bed system along with a discussion of its current capabilities and limitations. A brief outlook is presented for the project along with a discussion of a future cognitive nonlinear radar test-bed.

The goal of this project is to enable light-weight, durable, and portable systems capable of performing standoff detection of person-borne improvised explosive devices (PB-IEDs) through the development of millimeter-wave reflection-type phased arrays. Electronic beam steering eliminates the need for complex mechanical scanners that are commonly implemented with millimeter-wave imaging systems and would reduce overall system size and weight. We present a concept study of a 220 GHz reflection-type phased array for the purpose of performing beam scanning of a confocal reflector system. Requirements for effective imaging of the desired target region are established, including spatial resolution, total scan angle, and number of image pixels achievable. We examine the effects of array architecture on beam characteristics as it is scanned off broadside, including Gaussicity and encircled energy. Benchmark requirements are determined and compared with the capabilities of several potential phase shifter technologies, including MEMS-based variable capacitor phase shifters, switches, and varactor diode-based phase shifters.

The field of millimeter-wave (MMW) imaging has progressed significantly over the last two decades. The most obvious evidence of this is the widespread use of MMW full-body scanners, now commonly found in airports. The path to this point has been the result of the work of a wide range of experts from many scientific and engineering disciplines. This article represents one perspective of this progress. The development of MMW imagers, and all their associated component technologies, image processing techniques, clever engineering, etc. has been driven by a relatively small number of interesting applications. It has been known for about 70 years that RF energy can be used to "see" through things like clouds and detect, for example, hostile aircraft. As the RF frequency goes up to 35, 100, or 340 GHz, it becomes possible to image through obscurants with much improved resolution. However, as frequency increases, attenuation increases as well, so selecting the right frequency for the application is an important point. The challenge of seeing through obscurants such as fog, smoke and dust drives one towards a MMW imaging solution. Typical applications include guiding aircraft through low visibility conditions, detecting nearby watercraft in the fog, and searching for concealed weapons. So, while these capabilities have been demonstrated numerous times over the years, the practical and affordable implementation of the systems to accomplish these goals is where the real story lies.

This report explores the geometrical effects of a cylindrical chopper wheel on calculations of power coupling efficiency and noise equivalent temperature difference (NETD) of array elements. The overall efficiency of the cylindrical chopper wheel is found to be about 53% from geometrical arguments. In the limit that a detector beam fills the chopper aperture, if this efficiency is not accounted for, it can lead to detector NETD values that are a factor of 1.9 too high when calculated using standard double-modulation measurement techniques. For the particular geometry used with this setup, a power coupling efficiency of 78% was calculated for typical detector elements, resulting in values of detector NETD that were too large by a factor of 1.3 when the coupling efficiency was unaccounted for. This factor plays a role in accounting for some of the discrepancy between NETD values calculated based on diode sensitivity estimates and NETDs measured for individual array elements using double-modulation measurements.

The paper presents a three-dimensional imaging system for concealed object detection. The system uses interferometric imaging at terahertz frequencies. A three-dimensional spiral antenna array is used as the detection array. The data is collected at one array location at a time using an element that moves along the 3-D array line in order to prevent blockage. The data is processed using an accelerated computation hardware that matches the speed of the array element movement, and produces the image in real time. The system is simulated to show its advantage over the 2-D imaging system. An experiment is set to prove the concept.

We describe an active millimeter-wave holographic imaging system that uses compressive measurements for three-dimensional (3D) tomographic object estimation. Our system records a two-dimensional (2D) digitized Gabor hologram by translating a single pixel incoherent receiver. Two approaches for compressive measurement are undertaken: nonlinear inversion of a 2D Gabor hologram for 3D object estimation and nonlinear inversion of a randomly subsampled Gabor hologram for 3D object estimation. The object estimation algorithm minimizes a convex quadratic problem using total variation (TV) regularization for 3D object estimation. We compare object reconstructions using linear backpropagation and TV minimization, and we present simulated and experimental reconstructions from both compressive measurement strategies. In contrast with backpropagation, which estimates the 3D electromagnetic field, TV minimization estimates the 3D object that produces the field. Despite undersampling, range resolution is consistent with the extent of the 3D object band volume.

The Army Research Laboratory is in partnership with the University of Florida - Electronics Communications Laboratory to develop compact radar technology and demonstrate that it is scalable to a variety of ultra-lightweight platforms (

This paper describes an active millimeter-wave (MMW) holographic imaging system used for the study of compressive measurement for concealed weapons detection. We record a digitized on-axis, Gabor hologram using a single pixel incoherent receiver that is translated at the detector plane to form an image composite. Capturing measurements in the MMW regime can be costly since receiver circuits are expensive and scanning systems can be plagued by their long data acquisition times. Thus, we leverage recent advances in compressive sensing with a traditional holographic method in order to estimate a 3D (x,y,z) object distribution from a 2D recorded image composite. To do this, we minimize a convex quadratic function using total variation (TV) regularization. Gabor holograms are recorded of semi-transparent objects, in the MMW, mimicking weapons and other objects. We present preliminary results of 3D reconstructions of objects at various depths estimated from a 2D recorded hologram. We compare backpropagation results with our decompressive inference algorithm. A possible application includes remote concealed weapons detection at security checkpoints.

We analyze the impact of sparse sampling on millimeter-wave (MMW) two-dimensional (2-D) holographic measurements for three-dimensional (3-D) object reconstruction. Simulations address 3-D object estimation efficacy. We present 3-D object reconstructions from experimental data.

We apply structured passive elements and computational imaging to millimeter waves to enable a mobile imager. Experimental results are presented.

Passive millimeter wave (mmW) imagers have improved in terms of resolution sensitivity and frame rate. Currently, the Office of Naval Research (ONR), along with the US Army Research, Development and Engineering Command, Communications Electronics Research Development and Engineering Center (RDECOM CERDEC) Night Vision and Electronic Sensor Directorate (NVESD), are investigating the current state-of-the-art of mmW imaging systems. The focus of this study was the performance of mmW imaging systems for the task of small watercraft / boat identification field performance. First mmW signatures were collected. This consisted of a set of eight small watercrafts; at 5 different aspects, during the daylight hours over a 48 hour period in the spring of 2008. Target characteristics were measured and characteristic dimension, signatures, and Root Sum Squared of Target's Temperature (RRSΔT) tabulated. Then an eight-alternative, forced choice (8AFC) human perception experiment was developed and conducted at NVESD. The ability of observers to discriminate between small watercraft was quantified. Next, the task difficulty criterion, V50, was quantified by applying this data to NVESD's target acquisition models using the Targeting Task Performance (TTP) metric. These parameters can be used to evaluate sensor field performance for Anti-Terrorism / Force Protection (AT/FP) and navigation tasks for the U.S. Navy, as well as for design and evaluation of imaging passive mmW sensors for both the U.S. Navy and U.S. Coast Guard.

A research effort was conducted to explore the ways in which sub-wavelength gratings can be used to reduce the reflections from the optics of millimeter-wave imaging systems. A moth-eye lens is sometimes used at optical and infrared frequencies for this purpose, but it is too fragile to be applied directly to the plastic lenses used in the millimeter-wave. A modification of this structure, called the inverse moth-eye lens, was designed, fabricated, and tested. Within the report we present results at 35 GHz showing a 15-dB reduction of surface reflections in Rexolite. The technique was also applied to a material with a dielectric constant of 9. Transmission increased an average of about 30 dB between 30 and 40 GHz with the inverse motheye, anti-reflection (AR) surface. The implication of these results is that the weight and bulk of millimeter-wave imaging systems could be significantly reduced by using optical systems with high dielectric materials and etched, sub-wavelength AR surfaces.

We apply compression in the spatial frequency domain to generate millimeter wave images. Simulations indicate the efficacy of the approach. We are in the process of testing the system experimentally.

We describe a computational imaging technique to extend the depth-of field of a 94-GHz imaging system. The technique uses a cubic phase element in the pupil plane of the system to render system operation relatively insensitive to object distance. However, the cubic phase element also introduces aberrations but, since these are fixed and known, we remove them using post-detection signal processing. We present experimental results that validate system performance and indicate a greater than four-fold increase in depth-of-field from 17" to greater than 68".

A one-week experiment was conducted to determine the millimeter-wave transmission loss due to dust. Transmission data was collected at 35, 94, and 217 GHz through a recirculating dust tunnel. Dust clouds of various densities were measured during the experiment. The millimeter-wave measurements were non-coherent, using transmitting sources on one side of the dust tunnel and antenna/detectors on the other. The hardware was designed to minimize noise and drift. Even so, it was found that the transmission loss across the 1-m dust tunnel at high dust densities was lower than could be measured accurately with the equipment. Therefore, the results given are limited to system noise and represent maximum transmission losses at the various frequencies. The results show losses less than 0.02 and 0.08 dB for 94 and 217 GHz respectively across one meter of dust with density 3000 mg/m3. The actual losses are lower and a long baseline interferometer will be required to determine the loss values precisely. Despite the limitations of the experiment, the data show that millimeter-wave imager performance will not be significantly impacted by even a very dense dust cloud.

We apply extended depth-of-field imaging using a cubic phase element to a 94 GHz imager. Simulations indicate the efficacy of the approach. We are in the process of testing the system experimentally using a cubic phase element fabricated in Rexolite™.

Operation of military helicopters in a dusty environment challenges pilots with reduced visibility. Passive millimeter-wave (MMW) imaging has the potential to be used in these environments to image through dust cloud obscurants. The millimeter-wave phenomenology of the sand environment and the obstacles present in that environment are explored in this work. A 93 GHz polarimetric passive MMW imager was used to characterize an obstacle-rich sand environment and the results are presented. It is shown that there is a strong polarimetric signature present for both sand and cinder block between 10 and 30 degrees depression angles. Also shown is the phenomenology associated with shadows on sand. It was determined that berms and ditches can be very difficult to detect using even a sensitive MMW radiometer. The results can be used to model the performance of passive MMW imaging systems in a sandy environment.

The large numerical apertures employed in millimeter wave imaging are necessary for light gathering and resolution, but result in limited depth-of-field. We explore wavefront coding to extend the depth-of-field and examine effects on system performance.

This paper describes a passive millimeter-wave image scanner that leverages technologies previously developed for a video-rate passive millimeter-wave camera (PMC) [1, 2]. The imager has a prime focus elliptical frequency scanned antenna operating in the 75-93 GHz millimeter-wave band, a low noise receiver and a vertical beam former that allows the instantaneous capture of 128 pixel (vertical) column images in 1/30th of a second, with 2-3 K sensitivity. Two dimensional images are created by mechanically rotating the antenna, which produces a 128x60 raster image in 2 seconds. By integrating (averaging) images over a longer time period, we have demonstrated a sub-degree temperature resolution. This sensor has proven itself as a low cost tool for studying the potential of W-band passive imaging for various applications.

It has been demonstrated that passive MMW imagers can be used to detect obstacles through the fog, such as treelines and hillsides, which might be encountered in the path of a low-flying aircraft. However, the brightness temperature contrast between the horizon sky and the obstacle can often be quite small in foggy conditions, on the order of 5 K or less. Reliable detection of this contrast without image processing requires a passive MMW imager with a Δ-T min of about 0.2 K, which is quite challenging for existing 30-Hz imagers. While improvements in passive MMW imagers continue, it is useful to look at image analysis techniques that have the potential to improve obstacle detection by increasing the amount of information extracted from each image frame. In this paper we look at the ways that texture can be used to extract more information from the imagery. By merging textural information with the brightness temperature contrast information, there is the potential to enhance the detection of objects within the scene. The data used for the analysis presented here is 93-GHz, passive imagery of a deciduous treeline scene and a concrete building scene. The data were taken from the roof of a 4-story building to simulate the view of a low-flying aircraft. The data were collected over many months with an ARL-built Stokes-vector radiometer. This radiometer is a single-beam system that raster scans over a scene to collect a calibrated 93-GHz image. Texture measurement results for image segment samples, including autocorrelation and spatial edgeness, are presented in this work. Also presented are the effects of applying a modified Sobel edge detection technique to imagery with the least detectable obstacles.

Passive millimeter-wave (MMW) imagers have the potential to be used on low-flying aircraft for terrain-following / terrain-avoidance during low-visibility conditions. This potential exists because of the inherent nature of MMW radiation that allows it to penetrate many visible and IR obscurants such as fog, clouds, and smoke. The phenomenology associated with this application, however, has not been fully explored. Specifically, the radiometric signatures of the various obstacles that might be encountered during a low-altitude flight need to be thoroughly understood. The work described in this paper explores the 93-GHz passive signature of a deciduous treeline and a concrete/glass building. The data were taken from the roof of a 4-story building to simulate the view of a low-flying aircraft. The data were collected over many months with an ARL-built Stokes-vector radiometer. This radiometer is a single-beam system that raster scans over a scene to collect a calibrated 93-GHz image. The data show the effects of weather and tree lifecycle on the 93-GHz brightness temperature contrast between the horizon sky and the obstacles. For the case of trees, it is shown that the horizon sky brightness temperature is greater than that of the trees when the leaves are on because of the reflective properties of the leaves. This made the trees quite detectable to our system during the late spring, summer, and early fall. Concrete buildings are inherently low-contrast obstacles because their vertical nature reflects the horizon behind the sensor and can easily mimic the forward horizon sky. Solar loading can have a large effect on building signatures.

This paper presents our group's most recent passive millimeter-wave (MMW) measurements made using a 94-GHz Stokes-vector radiometer. Included are images and analyses of treeline data. These data were collected to investigate the possible use of passive MMW sensors to perform the helicopter collision avoidance task. The treeline data presented were collected in both the summer and winter. The results of the analysis show that in the winter the detection of the treeline can be straightforward because of an often-low horizon sky brightness temperature. The contrast between the tree branches and the horizon are seen in the data to be about 10 - 15 K. The summer case, however, shows a horizon sky-to-tree brightness temperature ratio of about 1. A simple statistical analysis of the summer image shows that the trees, in our case, can be distinguished from the horizon sky based upon the statistical parameters alone.

The US Army Research Laboratory has developed a 93-Ghz Stokes radiometer that is currently being used to quantify the polarimetric signature of various objects and materials. Preliminary measurement using the radiometer have been made of various terrain types and objects, which have included an asphalt aircraft runway, a gravel road, water, grass a tank, and a truck. A description of the development of the radiometer, its performance, and some initial results are presented. These results are the first step in assessing the utility of polarimetric radiometry and specifically how missions can be enhanced using this information. The results show that polarimetric radiometry may be useful for eliminating water as a false target in the imagery. It is also shown that asphalt aircraft runways do have a polarimetric signature that is different than short dormant grass at a 3-deg glide slope angle.

When pilots are flying at low altitudes, they need a sensor that can help them detect and avoid wires; this need remains a high priority for all U.S. military services. Many different sensors have been considered to fulfill this need. This report presents data that were collected on powerline wires of various diameters with the use of a 94-GHz radiometer. These measurements were conducted at short range in an effort to quantify the wire signatures and to determine if a millimeter-wave radiometer could be used to help pilots avoid wires. Data are presented for seven sizes of wire as well as for the horizon background of each wire. The results show that wires down to 1/4 in. in diameter can probably be detected reliably at ranges up to 200 m with a 94-GHz radiometer that uses a 3-ft antenna, provided that the signature of the horizon background can be characterized during flight. Beyond 200 m, the results show that an image-enhancement algorithm, if proven to be adequate, or a larger antenna will probably be necessary to reliably detect most standard powerline wires.

The authors present 94-GHz radiometric brightness temperatures of various clutter materials at nadir. The clutter materials measured include field vegetation, asphalt pavement, and an asphalt shingle roof and data is presented for each clutter type. We also report measurements that quantify the effect of water on the brightness temperature of metal. These measurements were made by adding calibrated quantities of water to a metal plate while recording the plate's millimeter-wave brightness temperature. Off-nadir data out to 45 deg is also presented for the field vegetation and asphalt pavement. Using a simple rough scattering model for the materials, we made estimates of the emissivity of the field vegetation and asphalt. The emissivity of the roof was determined by measuring its brightness temperature as it was heated.

The authors analyze properties of a 220 GHz imaging system that uses a scanned reflectarray to perform electronic beam scanning of a confocal imager for applications including imaging meter-sized fields of view at 50 m standoff. Designs incorporating reflectarrays with confocal imagers have not been examined previously at these frequencies. We examine tradeoffs between array size, overall system size, and number of achievable image pixels resulting in a realistic architecture capable of meeting the needs of our application. Impacts to imaging performance are assessed through encircled energy calculations, beam pointing accuracy, and examining the number and intensity of quantization lobes that appear over the scan ranges of interest. Over the desired scan range, arrays with 1 and 2-bit phase quantization showed similar array main beam energy efficiencies. Two-bit phase quantization is advantageous in terms of pointing angle error, resulting in errors of at most 15% of the diffraction-limited beam size. However, both phase quantization cases considered resulted in spurious returns over the scan range of interest and other array layouts should be examined to eliminate potential imaging artifacts.

Passive millimeter wave (pmmW) imagers are quickly becoming practical sensor candidates for military and nonmilitary tasks. Our focus was to adapt the Night Vision [U.S. Army Research Development and Engineering Command, Communications and Electronics Research Development and Engineering Center, Night Vision and Electronics Sensors Directorate (NVESD)] passive thermal infrared imager performance models and apply them to pmmW imaging systems for prediction of field performance for the task of small watercraft and boat identification. The Night Vision Lab's infrared sensor model has been evolving since the 1950s, with the most current model being NVThermIP [Night Vision Thermal and Image Processing (NVThermIP) Model Users Manual, Rev. 9 (U.S. Army RDECON, CERDEC, NVESD, 2006)]. It has wide recognition as an engineering tool for sensor evaluation. This effort included collecting pmmW signatures for a representative set of targets, conducting an observer perception experiment, and deriving the task difficulty criteria that can be used in NVThermIP for identification of boats. The task difficulty criteria are used by designers and managers to create systems capable of meeting specific performance criteria in the field.