17
The Camero, Inc., UWB Radar for Concealed Weapons Detection
James D. Taylor and Eyal Hochdorf
CONTENTS
17.2 State-of-the-Art CWD Systems
17.2.1 Summary of Body Scanning Technology
17.2.2 High-Resolution Body Scanners
17.2.3 Low-Resolution Standoff Screening Systems
17.2.4 Summary of Body Scanning Capabilities
17.3 The Camero UWB Radar Concealed Weapons Detection System
17.3.2 Designing the UWB Concealed Weapons Imaging Radar
17.3.2.1 Active Imaging Concepts
17.3.2.2 Design of Camero Concealed Weapon Detection Radar
17.3.2.3 Characteristics of Camero Concealed Weapon Detection Radar
17.3.2.4 Laboratory Demonstration of Camero UWB CWD Radar
17.3.2.5 Demonstration of Automatic Threat Detection
17.1 Introduction
Crowded public buildings, terminals, and transportation systems are the prime targets for anyone intent on killing large numbers of people, disrupting peaceful activities, and precipitating a major political or economic crisis. Security agencies need quick and reliable ways to detect concealed weapons, explosives, illegal drugs, and other contrabands. This chapter combines the search for concealed weapons, explosives, liquids, drugs, and other contrabands or forbidden materials under the general term “concealed weapons detection” (CWD).
At one extreme, CWD solutions include metal detecting systems and personal searches by authorized officials. At the other extreme, the shoe-bomber and underwear-bomber incidents raise the requirement to search for other concealed objects and substances. Terrorists have found and will continue to find new ways to get around security search and detection procedures. This war of wits drives the transportation security industry to search for new body scanning systems using passive millimeter waves (MMW), active X-rays, and UWB radar imaging to search individuals for concealed weapons and contraband [1].
This chapter surveys the state of the art in CWD security screening systems. We present the results of the research by Camero, Inc., and the demonstration of a high-resolution ultrawideband (UWB) CWD radar. The Camero CWD radar can provide real-time, standoff 3D imaging of multiple persons and can automatically detect the presence of concealed objects by looking for sudden changes in contour. We think that UWB radar can make a significant contribution to public security in airports, public buildings, and other high security areas.
17.2 State-of-the-Art CWD Systems
17.2.1 Summary of Body Scanning Technology
As of 2011, body scanning systems can image persons to determine the presence of concealed weapons, explosives, and other contrabands. CWD systems come in a variety of shapes from the security-checkpoint active body scanners to small, passive standoff units that can remotely image the passing crowd. Several companies now produce body scanning systems using X-rays or millimeter and terahertz wave imaging techniques. Table 17.1 summarizes some of the commercially available systems as of February 2011.
TABLE 17.1
Typical Concealed Weapons Detection Systems Available as of 2011
17.2.2 High-Resolution Body Scanners
The high-resolution body imaging CWD systems at airports or public buildings require each person to be scanned to enter the special area and either remain still or turn in a circle to complete the scanning process. Scanning and clearance generally takes less than 10 s. Figure 17.1 shows several typical state-of-the-art X-ray and active MMW imaging body scanners in use as of February 2011.
Body scanners take high-resolution front and back body surface images. They can detect objects hidden by clothing, including metals, plastics, explosives, drugs, etc. In early systems, CWD depended on the operator’s visual examination of each image and on specialized training. Figure 17.2 shows typical examples of images from backscatter X-ray and MMW scans. Note that the Smith’s B-Scan™ transmission X-ray system can detect objects concealed within the body [2-4,6,7].
Public concern and outrage over privacy issues caused manufacturers to develop image analysis software for detection of security threats. Now most full-image systems give the operator a visual clear indicator or a mannequin image showing concealed objects. The L-3 Communications ProVision™ and Smith’s eqo™ systems shown in Figure 17.1 have operator displays on the unit, which show a mannequin or a go-no go indicator [1].
17.2.3 Low-Resolution Standoff Screening Systems
Standoff passive systems search for concealed weapons by imaging the human body’s natural MMW and terahertz electromagnetic emissions. These video camera-type systems give realtime low-resolution imagery usable for remotely screening people. Metal objects, plastics, and other materials will block natural radiation and form shadows, giving an approximate indication of the location and shape of the suspect material. Figure 17.3 shows a typical example of a standoff passive electromagnetic system. Figure 17.4 shows how standoff systems give realtime images without the fine-grain resolution of the larger systems [5,8-10].
FIGURE 17.1
Typical total body scanning systems that can produce a high-resolution body image and automatically detect any concealed objects. Only the transmission X-ray system (b) can detect both external and internal concealed objects. Notice the go-no go operator display on the Smith’s eqo systems. (a) The Smiths detection eqoTM body MMW scanner requires the subject to turn 360° to complete the image. (b) The Smith’s detection B-SCANTM transmission X-ray system. (From Smith’s Detection, eqo Revolutionising people screening, 2010, http://www.smithsdetection.com/eqo.php; Smith’s Detection. B-SCAN transmission X-ray people screening system, http://www.smithsdetection.com/b-scan.php. With permission from Smith’s Detection, © 2010.)
FIGURE 17.2
Typical images from high-resolution backscatter X-ray body scanners. (Adapted from TSA, Backscatter X-ray technology: What do officers see? 2010; TSA, Millimeter wave technology: What do officers see? 2010.)
FIGURE 17.3
The Brijot Imaging Systems, Inc., GEN 2® passive MMW standoff screening system uses natural MMW and terahertz radiation of the body and looks for contrasts produced by concealed objects. (Adapted from Brijot Imaging Systems, Gen-2® Safe, Private effective full body scanning, www.brijot.com; ThruVision Systems, Our products, 2010, http://www.thruvision.com/Our_Products/Our_Products_Overview.htm; QinetiQ, SPO people screening security system, 2011, www.qinetiq.com/home/products/spo_20.html; With permission from Brijot Imaging Systems, Inc., © 2010.)
17.2.4 Summary of Body Scanning Capabilities
Security agencies require that CWD detection systems have the qualities listed in Table 17.2. Performance requirements such as probability of detection and false alarm raise the question of required performance versus cost and speed. At some point, the user must determine how much to demand for a given situation and assume the risk of an oversight or failure from an escalation of concealed weapons technology. We can envision a competition between security agencies and terrorists to find less detectable weapons and attack methods. Remember how the shoe and underwear bombers exceeded the capabilities of the existing CWD systems and thereby raised new security screening requirements.
FIGURE 17.4
Brijot Systems GEN 2® passive MMW scanner image with signal-processing indicator around the contrasting object, for example, a concealed pistol. Resolution: 6 cm × 6 cm. (Used with permission from Brijot Imaging Systems, Inc., © 2010.)
Each CWD technology has advantages and disadvantages as summarized in Table 17.3.
17.3 The Camero UWB Radar Concealed Weapons Detection System
17.3.1 Background
At Camero, Inc., we developed short-range, high-resolution UWB imaging technology for the Xaver™400 and 800 model through-wall radar systems. The antenna array configurations, signal acquisition systems, and time delay calibration subsystems described in Chapters 14 through 16 gave the Xaver™800 radar a high-resolution imaging capability, which can discriminate between moving and stationary objects behind a reinforced concrete wall. As shown in Chapter 14, this radar produces images that can discriminate between a man and a dog.
After establishing our baseline high-resolution imaging technologies, we applied them to the problem of concealed weapon detection. We decided to develop a body scanning system that would combine the standoff real-time imaging of passive MMW and terahertz wave technology with the high-resolution image quality of X-ray and MMW body scanning systems. We also hoped to provide the same imaging quality and improved performance at about half the cost of active scanning systems.
TABLE 17.2
Concealed Weapons Detection System Requirements
TABLE 17.3
Capabilities of Concealed Weapons Detection Technology
17.3.2 Designing the UWB Concealed Weapons Imaging Radar
17.3.2.1 Active Imaging Concepts
To increase the resolution and imaging capabilities of the UWB radar, we proposed to apply our imaging and signal-processing developments to two concepts: (1) a single system based on one antenna array and (2) a multiple-facets-coverage installation.
FIGURE 17.5
The single-radar CWD system concept for real-time scanning of moving people. The high-resolution UWB imagery can reveal the presence of concealed weapons, explosives, or other contrabands on people passing through the coverage area. This provides the operational benefits of the accuracy of high-resolution scanners along with the speed of passive standoff scanners. (Adapted from Hochdorf, E., Concealed weapon detection (CWD) program, Camero, Inc., 2010 (internal document). With permission from Camero, Inc., © 2010.)
The single-system concept uses one almost flat antenna array to scan persons passing in front of the array at a distance of 1-3 m as shown in Figures 17.5 and 17.7. This configuration allows wall mounting or concealing of the system behind an RF-opaque panel. As designed, the system can only provide coverage of half of the person, with possible blind areas on the side away from the antenna array. Note the slanted wings on the antenna array that should help to give total body imaging with limited movement of the person.
The Camero UWB CWD system can masquerade as a wall in a traffic choke point to reduce the probability of evasion. Our design overcomes the problem with the Smith’s Detection eqo™ system, which requires the subject to turn their body 360° to complete the scanning process.
The multiple-facets concept uses several synchronized UWB imaging radar systems to provide 3D imaging of passing persons. Figure 17.6 shows the multiple-facets concept with two variations. One version uses several synchronized systems along a corridor or a corner to cover both the front and back sides of a person simultaneously. The reflector version uses the single-antenna installation with a set of mirrors to give 3D coverage of passing persons. This gives 3D coverage with only one antenna array.
17.3.2.2 Design of Camero Concealed Weapon Detection Radar
We developed sophisticated UWB imaging technologies for the Xaver™400 and 800 series through-wall radar systems described in Chapters 14 through 16. Our developments included antenna array optimization, signal-to-noise improvement, and time delay calibration methods for each transmitter-receiver channel. Having developed the basic components for high-resolution UWB radar imaging, we decided to develop a radar system that could provide better detection of concealed objects than the body scanning systems described in Table 17.3. Our design process included these considerations:
FIGURE 17.6
The multiple-facets CWD system has two possible configurations: (a) Two synchronized UWB imaging radar systems that can track, image, and search a person for concealed weapons or contrabands. (b) A single-antenna system with reflecting plates to provide 3D imaging as the person moves through the search area. (Adapted from Hochdorf, E., Concealed weapon detection (CWD) program, Camero, Inc., 2010 (internal document). With permission from Camero, Inc., © 2010.)
Frequency selection: Based on our previous work, we decided on a micropowered step recover diode (SRD) radar operating in the 3-10-GHz frequency range. This would provide an inexpensive and reliable transmitter and avoid the expense of MMW and terahertz technologies.
Antenna array design: To achieve high resolution and 3D imaging, we proposed an antenna with 192 transmitters dispersed over the aperture in two polarities (vertical and horizontal). Each transmitter emits for a short time period only during each frame, giving a relatively low duty cycle and eliminating cooling problems.
Transmitter control: Each transmitter sends 16 pulses during each phase, which gives a scanning rate of eight frames per second. Each transmitter sends a pulse once in every 83 ns (12-MHz pulse repetition frequency), which reflect to all receivers. Our system sequentially collects the returns to make 9216 data channels for each polarity and cross polarity totaling 36K channels. After alignment and filtering, the data channels become the input to a sophisticated 3D image reconstruction process.
Maximum imaging range: Data-processing considerations will limit the maximum range. Based solely on the PRF, we could have a maximum range of 12.5 m. Because we must perform serial scanning with our digital data system (DDS), this means we have to wait for each range cell to integrate enough signal power. With a sampling frequency of 21 GHz, we have to sample range increments of 0.71 cm. We could scan any range until we hit the folding point at 12.5 m. Based on eight frames per second, we had to decide how much time to spend in each range cell and how many range cells we could cover. We also had to account for the relative distance from various channels. High resolution requires a large array size, so channels with transmitter and receiver elements at the array corners have a longer range to a given reflector than the channels in the middle of the array. This requires accounting for the offset as well. To meet the timing requirements and frame rate, we settled for a 3.5-m effective scanning range. However, to get all the channels to participate, we had to reduce the scanning range to 2.5 m.
Image processing: We propose to process the 3D images to search for objects that disrupt the human skin’s smooth reflection characteristics. The system presents images with a fast rendering machine with various display options and filters. The CWD radar has a relatively large front end associated with analog transmitters and receivers. Several NVIDIA™ graphics processor cards located in backend computing stations handled the calculations needed to form an image [14].
17.3.2.3 Characteristics of Camero Concealed Weapon Detection Radar
The Camero CWD radar has the following design characteristics:
Transmitted power: The CWD radar operates in the 3-10-GHz UWB frequency band and requires a radiating power less than 1 mW. This makes the CWD radar safe for human exposure. Given this power level, it meets the level for FCC approval, as do other Xaver™ series products.
Active imaging: The CWD radar does continuous active imaging without requiring any cooperation of the person scanned.
Environment: The CWD radar can work in a wide range of indoor and outdoor conditions. It does not depend on the installation location. High-resolution body scanners require an indoor or sheltered operating environment. Low-resolution passive MMW systems have high temperature sensitivity in indoor environments with only small temperature variations.
Detection reliability: 3D imaging enhances the reliability of detection relative to the 2D images in passive MMW, X-ray backscatter, and multifocal-CW-based active MMW systems. This gives us considerable ability to extract objects close to the body rather than by detecting the 2D projection.
Operating frequency band: The CWD radar will operate in the UWB frequency band (3.1-10.6 GHz) that is already FCC-approved and safe for consumers. The nonionizing radiation can detect a wide variety of materials including liquids and jells.
Real-time operation: We can build an entire array to give 3D real-time imaging. Using UWB frequencies lower than MMW systems (20-30 GHz) with a similar bandwidth makes a more cost-effective design for 3D imaging.
High throughput: The full 3D-imaging antenna array eliminates conventional scanning that requires a person to enter a chamber or turn around in place for being detected. The CWD radar generates a real-time 3D video stream that allows scanning more people in a given time and increases throughput compared with other high-resolution systems.
Low maintenance: The CWD radar has no moving parts and has a self-calibrating feature based on the time delay calibration system described in Chapter 16.
Table 17.4 summarizes the capabilities and the performance of current technologies compared with those of the UWB radar. The Camero UWB 3D CWD radar can provide a major improvement through standoff real-time imaging, which enables a high throughput with lower costs.
TABLE 17.4
Performance of Concealed Weapons Detection Technologies
17.3.2.4 Laboratory Demonstration of Camero UWB CWD Radar
We tested the CWD radar concept using a single-polarity prototype. Time domain signals from the single-polarity array fed a sophisticated 3D image reconstruction processor using NVIDIA™ graphics processor units. Later we can add a fast-rendering software to permit observing the 3D image in any desired orientation. The image processing and display system of the CWD radar will have an automatic detection system for identifying concealed objects and a simplified “pass or fail” operator display for privacy.
Figure 17.7 shows frames taken from real-time radar images along with the antenna array. Figure 17.8 shows another set of frames enhanced for contrast, showing moving men with weapons. Even without the increased contrast, we have an extraordinarily detailed picture of the moving men. The resolution and detail exceed those of the X-ray backscatter and MMW SAR images shown in Figure 17.2. We consider that the prototype images show considerable promise for a successful CWD system.
17.3.2.5 Demonstration of Automatic Threat Detection
Our 3D radar images reveal considerable personal details, which can lead to privacy issues in the course of operational use. Anticipating the privacy issue and looking at the capabilities of other systems, we developed an automatic detection system. This processor examines the image surfaces for sudden changes in contour, thereby indicating articles concealed under clothing.
We consider that using 3D imagery and contour contrast detection for automatic threat detection (ATD) can provide an improved reliability in detecting all concealed objects, with less chance of false alarms. We started our ATD work by using the Xaver™400 through-wall radar array to prove that we could use UWB radar to form a usable image. After taking a number of different scans of a mannequin, we constructed the image in Figure 17.9a to demonstrate the concept of 3D imaging with a UWB array. Using contour contrast analysis, the automatic detection system has identified the object and placed a colored indicator over it. Our process of analysis of surface-contour interruption detected the objects, which are highlighted as shown in Figure 17.9b.
FIGURE 17.7
A Camero real-time 3D-imaging demonstration using the 192-transmitter array shown in the upper-right inset. The sequence of images shows a person reaching into a pocket, removing a cell phone from the pocket, and using it. The cell phone stands out as a raised area on his left thigh. (Used with permission from Camero, Inc., © 2010.)
In the interest of privacy protection, future versions could then translate the image into a mannequin image or an indicator display, so that the security officer can search that particular person or allow that person to pass.
17.4 Conclusions
The results of the high-resolution imaging UWB radar demonstration show great promise for applications such as security screening and concealed weapons detection. We can see a long-range development of UWB radars for both surface and internal imaging. Medical applications such as microwave tomography using UWB techniques will also develop, as shown in Chapters 5 and 9. Adding the capability of internal body imaging to the detection system could aid in searching for contraband such as drugs and explosives carried in body cavities. Perhaps a variation of the surface-contour contrast analysis could provide an automatic detection system for this type of threat. We can also foresee more health-related and diagnosis-related applications of the Camero high-resolution UWB imaging radar.
FIGURE 17.8
The Camero prototype CWD can produce high-resolution real-time 3D imagery. We have enhanced the contrast of selected frames for better print reproduction. (a) Man turning toward the array. (b) Man holding a pistol (with fig leaf added). (c) Two moving men. (d) Rear view of the man with an object on his right thigh. (Used with permission from Camero, Inc., © 2011.)
FIGURE 17.9
The Camero proprietary ATD software searches for sudden changes in contour in 3D image surfaces and adds a colored indicator over concealed objects. This early demonstration used a mannequin imaged by a Xaver™-400-based imaging radar with multiple passes. (a) The image before processing. (b) After processing, the detection system places a colored indicator over concealed weapons and objects. (Adapted from Hochdorf, E., Concealed weapon detection (CWD) program, Camero, Inc., 2010 (internal document). With permission from Camero, Inc., © 2010.)
Acknowledgment
Special thanks to Eyal Hochdorf, the Chief Technology Officer of Camero, for providing the concept and information on UWB radar for this chapter and for reviewing the manuscript.
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