To combat the ever-present threat to homeland security, photonic companies and research institutions are constantly developing new imaging technologies aimed not just at target identification, but also at maintaining constant and enduring contact with the target after identification.
Iris on the Move (IOM) technology from Sarnoff (Princeton, NJ) was designed specifically for identification of a moving target. Homeland-security applications might involve identifying an unknown person in a crowd of known persons, so IOM technology was created to rapidly image the iris of individuals passing through a checkpoint or other processing station and compare those images to a known database (see Fig. 1).
The IOM technology uses biometrics—the analysis of biological data (unique human features) for identification. “Iris recognition is the most accurate approach to biometric identification because the patterns contained in a human iris are unique and stable over time,” says Ray Kolczynski, Sarnoff’s IOM product manager. “Until now, the capture techniques have been cumbersome, requiring subjects to stop, position themselves in front of a camera and remain there for several seconds. But Sarnoff’s IOM system captures a sufficient iris image from an unprecedented 30 people per minute situated up to 3 m from the camera, using a fast shutter and strobed, synchronized, high-power 850 nm near-infrared LEDs, shown to provide the best iris imaging characteristics necessary for recognition.”
Kolczynski says that a good-quality iris image should have 200 pixels across a 1 cm iris. By using a four-camera array of 2048 × 2048-pixel video cameras with a 210-mm-focal-length lens, Sarnoff increases its capture volume to image people 5 to 6.5 ft tall while still maintaining acceptable quality for iris identification.
When a target is beyond the 30-people-per-minute realm and on the run, some imaging systems fail to keep the target in view when a shutter interrupts image tracking. In microbolometer-detector-based infrared (IR) cameras, the shutter is necessary to perform nonuniformity correction for individual pixel variations due to thermal drift. To address this issue, Thermoteknix Systems (Cambridge, England) developed shutterless XTi imaging for its MIRICLE microbolometer cameras that functions over the full temperature range of the camera. Operating at 60 Hz in standard cameras (and up to 240 Hz in special applications), the output analog or digital video can be locked for frame-to-frame indexed operation and target tracking, particularly when the target is at a temperature different from that of its surroundings.
Undercover imaging
When only covert imaging will do, companies like Swann Communications (Richmond, Australia) offer FlashlightDVR compact digital video recorders concealed in a portable flashlight for border-protection applications, as well as PenCam DVRs–mini video cameras and recorders concealed in a ballpoint pen.
But a lesser-known option for covert tracking is a new imaging technology called GPSit from the company with the same name, GPSit (San Diego, CA). GPSit is currently a 1/2-in.-thick package that sends GPS data to a remote terminal for cargo-tracking applications. By the Q3 2009, GPSit says the device–reduced to 1/4 in. thick–will house a miniature camera, imaging sensors, and electronics packed together in a super-thin flexible plastic embedded within “Tough Skin.” The skin can be of any form, appearing to an intruder as a sign, bumper sticker, or any type of label. The covert sensor will take images, collect voice, GPS location, and other important data and send it wirelessly to a remote analysis station. The imaging system will incorporate a 256 × 256-pixel CCD sensor with at least 32 gray levels activated by a light sensor. “With a field of view of 60° at one-meter distance, GPSit could also be deployed for night-vision applications using an IR sensor when covert operations are essential,” said Rick Conner, GPSit product director.
Seeing hidden threats
“Backscatter imaging” x-ray machines and millimeter-wave systems installed at airports for passenger screening just a few years ago (and in many ways inadequate because they are unable to see through rubber or plastic materials that resemble skin) are paving the way for terahertz-based systems. TeraView (Cambridge, England) has demonstrated a handheld terahertz scanner for future airport screening applications. And Picometrix (Ann Arbor, MI) recently won a Phase II SBIR from NASA for its T-Ray 4000 system to image aircraft components for structural flaws and voids–a 3-D tomographic imaging capability that could also be deployed for cargo screening.
Because the high cost of terahertz systems continues to hinder commercial implementation, researchers are seeking lower-cost options. A terahertz alternative from the University of Warwick (Coventry, England) uses near-IR light–around the wavelengths found in domestic remote controls–in conjunction with a special analog signal recovery technique once commonly used in astronomy.3 This technique, while sophisticated, uses readily available optoelectronic components and is inherently far more portable than currently available commercial alternatives. The near-IR 700 to 900 nm narrowband source detects variations in the transmitted or reflected intensities of an object. Photons with this energy have relatively low levels of electronic and molecular interaction, and transmission through an object is almost entirely a function of thickness (absorption) and specimen particle size (scattering), permitting rapid and real-time detection of concealed objects (see Fig. 2).
Visible-wavelength and IR cameras continue to play the largest role in uncovering hidden threats. Push-broom hyperspectral cameras rapidly image each line in a scene, optically dispersing it in the axis perpendicular to the line. This two-dimensional image is projected on a high-speed camera operating in the wavelength range of interest. Under similar illumination conditions and measurement times, push-broom cameras have higher throughput than acousto-optic tunable-filter-based cameras by a factor of 30 and liquid-crystal tunable-filter-based cameras by a factor of 15.4
Specim (Oulu, Finland) and its partner Middleton Research (Middleton, WI) have developed a short-wave-IR and very-near-IR dual camera for the 400-to-2500 nm range, and a wide-angle computer-controlled survey scanner for mining and other geological applications. Hyperspectral imaging and chemometric data processing can help detect security threats such as a chemical spill. Real-time data compression using chemometrics is performed by a dedicated high-speed Prediction Engine module developed by Middleton Research. The output of the Prediction Engine is the calculated composition or other parameter extracted from the spectrum and calculated at each point with sustained full camera speed, readily identifying the agent of interest in the scene.
Because push-broom hyperspectral imaging requires either the imaging sensor to move over the scene, or the scene to move under the sensor, Headwall Photonics (Fitchburg, MA) recently developed its Pan & Tilt Hyperspec system. “Pan & Tilt enables hyperspectral imaging in a stationary manner,” says David Bannon, Headwall CEO. “Mounted on a stationary platform or boom, the motorized pan and tilt sensor rapidly scans a scene for detection and display of unique spectral signatures, such as concealed objects or vehicles within the sensor’s wide field of view.” Bannon describes the typical application of “spectral tagging” in which objects or people are tagged with unique spectral identifiers (sprayed on a border fence, for example) for surveillance tracking. “These instruments have additional bays to accommodate thermal cameras, other Hyperspec sensors for a different spectral range, or even small LIDAR units, allowing homeland-security organizations to build ‘sensor suites’ with a range of capabilities.”
And finally, night-vision capability is moving well beyond the analog goggles of yesteryear. Intevac Photonics (Santa Clara, CA) is nearing completion of the development phase for its Night-Port Electron Bombarded Active Pixel Sensor (EBAPS) imaging system. Night-Port’s EBAPS utilizes CMOS technology to produce a high-resolution, low-light-level, real-time video for “record and playback” by law enforcement, border patrol, or first responders. Night-Port performs on-board image processing for a high-contrast image on its 1280 × 1024 three-color pixel display. With or without its built-in IR illuminator, a homeland-security threat cannot hide in the dark.
REFERENCES
- D.W. Pendall, Military Review (Nov-Dec, 2005).
- L. Ozyuzer et al., Science 318(5854) p. 1291 (Nov. 23, 2007)
- G. Diamond, SPIE Newsroom, DOI: 10.1117/2.1200808.1219 (Aug. 14, 2008).
- T. Hyvarinen et al., Hyperspectral Chemical Imaging, Application Note from Specim, Oulu, Finland (2007).
Persistent surveillance
Several people at defense companies who were interviewed for this story mentioned the term “persistent surveillance,” but were not willing to disclose their “proprietary” homeland-security imaging technologies. A 2005 Military Review article by U.S. Army Major David M. Pendall noted that the idea of “persistent surveillance” had already been around for at least three years.1 When global or local reconnaissance finds something or someone of actionable interest, “persistent surveillance” may be used. As defined by Pendall, “persistent surveillance” is the intelligence, surveillance, and reconnaissance (ISR) persistent stare, in which processing and analytic systems maintain constant and enduring contact with the target, making it unable to move, hide, disperse, deceive, or otherwise break contact with the focused intelligence system–essentially denying the adversary any sanctuary. Many of the technologies discussed in this article are designed with persistent surveillance applications in mind.
