Introduction. Need for Integrated Container Inspection System (ICIS)

Transcription

1 Introduction Advanced Cargo Container Scanning Technology Development Victor Orphan, Ernie Muenchau, Jerry Gormley and Rex Richardson Science Applications International Corporation San Diego, California The terrorist use of a cargo container to smuggle a nuclear weapon or radiological material which could be used in a radiological dispersion device (RDD) is a serious threat currently being addressed by the US and other governments. The US government has negotiated through the Container Security Initiative (CSI) placing Customs and Border Protection inspectors in 20 major overseas ports to help ensure that cargo containers bound for the US do not constitute a threat. CSI and other initiatives to help secure the supply chain, such as CT-PAT (Customs Trade Partnership against Terrorism) are effective initial efforts to protect against terrorist use of cargo containers to launch a WMD (weapons of mass destruction) attack. However, the 7 million containers which enter the US by sea every year present a difficult inspection challenge. Currently, only a relatively small percentage (~5-6%) of containers, those deemed high threat containers, are physically inspected usually using non-intrusive scanners (either gamma-ray or x-ray) to detect contraband hidden within the cargo. Advancements in cargo container scanning technologies are needed to further enhance the security of cargo containers without disrupting the essential flow of cargo. The economic consequences of a successful WMD attack by terrorist involving cargo containers are potentially catastrophic since an attack could lead to a shut-down of the supply chain for an extended period. Improved container scanning technologies hold the key to expeditiously re-starting the supply chain postattack. We describe the development of an Integrated Container Inspection System (ICIS) which combines existing technologies (Portal VACIS, Radiation Portal Monitors and automated container identification using OCR) into an optimized system which enhances the ability to detect nuclear or radiological material in a cargo container. In addition, two significant enhancements to VACIS, the gamma-ray radiographic inspection system widely used for inspecting cargo containers, are discussed: (1) a next generation gamma-ray imaging detector which provides a factor of ~4 improvement in spatial resolution and (2) automated empty container detection using a Portal VACIS and automated image analysis software. Need for Integrated Container Inspection System (ICIS) The primary detection technique for nuclear weapons, nuclear and other radioactive materials is passive gamma-ray and neutron detection using large area, high efficiency detectors which permit threat levels of radioactivity to be detected at practical scanning speeds (up to 30 km/hr is required in some cases to avoid impacting cargo throughput). If the radioactive source is heavily shielded by dense, high-z material the passive detection technique may fail to detect the source. In this case, a complementary technique, such as x-ray or gamma-ray radiography can aid by detecting the dense material. Imaging will 1

2 also help verify that the cargo container contents are consistent with the manifest; thus, helping to resolve nuisance alarms from naturally radioactive material commonly found in cargo (for example, ceramic tiles, porcelain toilet bowls, kitty litter, etc.) The primary Radiation Portal Monitors (RPM) typically are unable to determine the specific radionuclide(s) responsible for initiating an alarm. Thus, containers triggering an RPM alarm require secondary inspection. A handheld isotope identification system can perform a gamma-ray spectroscopic analysis near the suspect region of the container and determine the specific isotope causing the alarm. This measurement is essential for identifying nuisance alarms and allowing expeditious disposition of cargo in secondary inspection. A material-specific non-intrusive technique such as fast and thermal neutron elemental analysis can aid in verifying the presence of WMD materials such as explosives, chemical agents, and nuclear materials (such as highly-enriched uranium) which cannot usually be detected passively but can be detected using neutrons to induce fission in the U-235. When processing hundreds of containers and trucks per day at a sea or land border port with multiple traffic lanes, it is essential to automate the positive identification of the container and truck. For instance, this will ensure that the alarming truck or container is properly directed to secondary. Fortunately, technologies for (automatic license plate readers) and cargo containers identification (video OCR systems) have been developed for logistics purposes and can be readily adapted for security applications. ICIS Description ICIS consists of one or more Sensor Subsystems at the terminal gates, quay or other locations; the ICIS Server, which integrates and stores sensor data; and the ICIS Viewer, which provides a graphic display of the integrated data. Each Sensor Subsystem can be equipped with SAIC s advanced gamma ray imaging, radiation scanning and OCR technologies. Following are descriptions of the ICIS components. Gamma-ray Radiographic Imaging SAIC s Vehicle and Cargo Inspection System (VACIS ) gamma ray imaging technology provides clear radiographic images (much like x-ray images) of containers, showing the outlines and density of the contents. With its very low radiation dose, the VACIS scan is much safer than comparable x-ray systems. Over 170 VACIS units have been purchased by the US Government (Customs and Border Protection and the Defense Department) and foreign customs agencies for use at cargo facilities around the world. The principle of operation of VACIS is similar to that of a line-scan x-ray system; except, VACIS uses a gamma-emitting radioisotope. The source, consisting of a pellet a few mm in diameter, is collimated to project a fan-shaped beam onto a linear array of very sensitive NaI-photomultiplier scintillation gamma-ray detectors. The gamma-ray energies are 662 kev for cesium-137, and an average of 1253 kev for cobalt-60. The heart of all VACIS products is SAIC s patented (U.S. patent number 6,507,025B1) highefficiency photon-counting technology. Portal VACIS and Mobile VACIS have both been integrated with the Exploranium RPM. Unless mobility is required, the Portal 2

3 VACIS is optimum for use in the integrated system. Following are brief descriptions of each. Mobile VACIS is extremely well suited to the port environment, and is designed around a standard vehicular platform that can be easily serviced and repaired. The Mobile VACIS, shown in operation at a port in Figure 1, can be driven to an inspection point within a port, and set up and operational in less than 10 minutes. It does not permanently occupy scarce port real estate and requires only a minimal footprint to perform inspections of the cargo at hand. It can operate in both the scanning mode in which the truck/container is stationary or in the stationary mode where the truck or container is driven past the Mobile VACIS gamma-ray beam. Figure 1. Mobile VACIS in use at seaports to inspect cargo containers Portal VACIS is a high-throughput imaging system for port gates and roadways and provides a quick and effective tool to detect high-value stolen goods before they leave the country, or illegal materials smuggled into the country. Engineered to operate in very small areas, Portal VACIS can be deployed in conjunction with existing vehicle control points, such as weigh scales, and provides permanent protection to port gates and roadways. Figure 2 shows the geometry of Portal VACIS which uses two opposing sources and detector arrays which facilitate imaging an entire container or truck without requiring sourcedetector separation distances greater than the width of a standard road lane. Thus, Portal VACIS units can be installed on adjacent multiple lanes. The prototype Portal VACIS used to verify that empty trucks entering Mexico were indeed empty is also shown in Figure 2. Figure 3 shows two Portal VACIS units installed on adjacent traffic lanes at the Mexican seaport of Manzanillo. Portal VACIS can scan at speeds up to 8 km/hr allowing it to be used in tandem with a RPM in the integrated system without impeding the flow of vehicles. The gamma beams are shuttered off as the tractor passes the area of the beams. Once the tractor and driver have cleared the beam area, fast-acting shutters open to allow imaging of 3

4 the container (being pulled through on a chassis) or cargo portion of a truck. The speed of the vehicle during the scan is monitored by a radar gun and used to correct the image distortion resulting from variable speed during a scan. The tight collimation of the gamma beams ensures that the driver receives no radiation dose. A stowaway in a scanned container would receive less than 5 microrem (0.05 microseiverts), equivalent to about 15 minutes of natural background radiation at sea-level. A VACIS average radiation dose to cargo is more than an order of magnitude less than the lowest dose 450 kv x-ray system and about three orders of magnitude less than that of a 2 to 6 MeV x-ray system. (1) Gamma Ray Source No. 2 Detector Tower No. 1 with Shielding Detector Tower No. 2 with Shielding Gamma Ray Source No. 1 Figure 2. Portal VACIS schematic (upper) and prototype used by Mexican Customs at US border to inspect empty trucks (lower) (1) Siraj Khan, Paul Nicholas, and Michael Terpilak, Radiation to Stowaways in Vehicles, Proceedings of 2001 ONDCP International Technology Symposium, June 25-28, 2001, San Diego, CA 4

5 Figure 3. Two Portal VACIS on adjacent traffic lanes at Manzanillo Port in Mexico Radiation Scanning Radiation portal monitors (RPMs), consisting of large-area gamma-ray detectors (usually plastic scintillation detectors) and neutron detectors (He-3 detectors in polyethylene moderator material), allow the passive detection of nuclear materials or other radioactive materials to be detected in cargo containers or trucks entering or leaving a port. The high detection sensitivity of RPMs allows 100% scanning of cargo with minimal impact on throughput. However, false positive alarms resulting from cargo which is naturally radioactive (e.g., certain ceramic materials, kitty litter) can slow-down the flow of commerce unless efficient means are provided for resolving these false positives. Figure 4 shows RPMs installed at the Port of Felixstowe in the UK under a pilot program. RORO (roll-on, roll-off) cargo entering this port is scanned by a gamma-neutron passive portal monitor. Those trucks which alarm at the primary detection station are diverted to a secondary inspection station where the truck is radiographed (either gamma-ray or x-ray) and a handheld isotope identifier unit is 5

6 used to determine the specific radioisotope responsible for triggering the portal monitor alarm. Figure 4. Radiation Portal Monitors installed at Port of Felixstowe (UK). Automated Vehicle and Container Identification SAIC s advanced OCR technology reads the ID number of each container, enabling ICIS to automatically associate VACIS and RPM scanning data with specific containers. SAIC OCR systems at terminals around the world currently identify millions of containers and vehicles annually. One such system recently deployed at the American President Lines terminal at the Port of Los Angeles, shown in Figure 5, automates the access control of trucks bringing cargo containers to the terminal. Video cameras scan the cargo container from several directions to image the container identification number which is automatically read using OCR software. Chassis identification numbers and the truck license plate are similarly imaged and recorded. 6

7 Figure 5. OCR System at APL Terminal in Los Angeles Material Specific Scanning using Neutron Interrogation PELAN uses pulsed 14 MeV neutrons from a small neutron generator to excite characteristic gamma-rays from nuclear reactions. Automatic analysis of the resulting gamma-ray spectra provides a measure of elemental compositions of carbon, oxygen, nitrogen and hydrogen which can verify the presence of explosives or chemical agents. Figure 6 shows SAIC s PELAN being used to verify the presence of explosives in a van. 200 lbs ANFO Figure 6. SAIC PELAN detecting 200 lbs ANFO Explosive in van. 7

8 Integrated Display (ICIS Viewer) Figure 7 shows ICIS at SAIC s Rancho Bernardo (San Diego) facility and an integrated display of the VACIS gamma radiographic image with the Exploranium RPM trace (total counting rate and counting rates from energy windows as a function of position along the vehicle) properly registered. The RPM background level can be increased (impacting sensitivity) if the RPM is located close to the VACIS gamma-ray source. Thus, the RPM should be located at least 30 m from VACIS source unless additional shielding is used. Therefore, means for spatially correlating the RPM and VACIS data relative to the truck or container have been developed. Figure 7. ICIS prototype being tested at SAIC s San Diego facility (upper) and ICIS integrated display computer screen. 8

9 For added flexibility, the ICIS sensor subsystems are available in both fixed and mobile configurations. The mobile subsystem can be set up in minutes virtually anywhere in the terminal ideal for inspecting containers on the quay. The mobile subsystem communicates with the ICIS Server over a high-speed wireless network. ICIS can also include other capabilities to streamline terminal operations, such as SAIC s EmptyView system to automatically verify empty containers, and enhanced cameras and viewing software for online damage inspection. ICIS Benefits With these capabilities, ICIS offers significant benefits for Customs. ICIS systems installed at U.S. ports of entry would enable CBP to screen a large percentage of inbound containers to identify high-risk containers. And installed at foreign terminals around the world, ICIS would enable CBP to screen a large percentage of containers bound for the U.S. before they ever reach our shores. Terminal operators around the world have economic incentives to integrate ICIS systems into their operations because such systems would add value for their customers. Perhaps most important, ICIS scanning, as part of CBP security procedures, may help qualify containers for expedited processing, thereby reducing shipping costs. In addition, terminal operators can assure their customers that their terminals are less vulnerable to terrorist activity, and will reopen faster in the wake of an incident or threat at the terminal or elsewhere. SAIC anticipates that these economic incentives will promote the adoption of ICIS within the industry accelerating the enhancement of security for CBP. ICIS Demonstration at Port of Hong Kong SAIC is currently in discussions with the Hong Kong Container Terminal Operators Association (CTOA) regarding a fully integrated ICIS demonstration system. The goal of the project is to demonstrate to Customs authorities and the global port community that ICIS can scan all inbound export containers as part of the terminal s normal operations without impeding traffic, and that the information it provides will help Customs authorities identify high-risk containers for further inspection. As currently envisioned, SAIC will install a prototype ICIS system (including one or more VACIS units, RPMs and OCR components) to scan export containers entering the terminal by truck or barge. With its high capacity, the system will handle the terminal s full volume of up to 14,000 Twenty-Foot Equivalent Units (TEUs) per day. The information from the ICIS sensor components will be integrated by the ICIS Server for evaluation by Customs and others. SAIC intends to begin the demonstration project in Fall Automatic Empty Container Verification System Introduction Many inter-modal terminals expend significant resources verifying that shipping containers designated empty are actually empty at terminal gates. Typically, truck drivers park in the gate lanes or in a dedicated inspection area, exit the truck, and open the rear doors so that an inspector near the truck or at a central video station can visually verify that the container is empty. This process can take a minute or more per truck, 9

10 wasting hours of gate and inspector time every day and putting drivers and inspectors at risk in traffic. We describe and show performance results for an automatic empty container verification system (patent pending) which provides a faster, safer solution. The system automatically scans closed containers as trucks drive through, detects objects inside, and alerts inspectors for non-empty containers. Gamma-ray scanning technology images the interior of closed containers moving at up to 10 mph (16 km/h) in 5 10 seconds. Automated software analyzes the container image to detect objects inside the container, including pallets and other wooden objects, cardboard boxes, even plastic wrap. When an object is detected, it issues an alert to inspectors or the terminal s information system. The system has demonstrated a probability of detection of about 97%. Configuration The system uses a Cs-137 source of photons. The gamma-ray energy of 662 kev provides good contrast for a wide range of materials, including small amounts of wood, cardboard, etc. The detector array is a single column of relatively large scintillation photon detectors to enable efficient photon detection and better counting statistics. A change from the COTS version of the Portal VACIS is in the beam angle. COTS Portal VACIS systems are intentionally designed to offset the collimated source beam angle at about 10 degrees from perpendicularity to allow an oblique view through front and back walls of a container. This was a feature requested by operators since this is a favored location for false compartments, etc. and the oblique angle-of-incidence makes such compartments easier to detect. However, it was easier to develop automated algorithms to reliably detect front and rear walls with a truly perpendicular beam. This also significantly improves the ability to detect small objects placed against these walls. A single operator s booth can be used to monitor several lanes of outbound traffic. This is because the image analysis software operates essentially autonomously, and only requires operator intervention in the rare cases when the algorithm is uncertain of its results or if a container is actually non-empty. CONOPS (Concept of Operations) Some of the operational aspects depend upon the business rules in use at a particular site. A generalized operational concept is discussed here. The EmptyView portals are setup on the outbound lanes of a terminal. There is a gate and driver-activated button on an extended arm in the appropriate position to be reached from a truck cab when stopped at the gate. When the driver presses the button, the gate lifts, allowing the driver to proceed. As the driver pulls away, the EmptyView portal records the gamma-ray scan and vehicle speed. An additional capability currently in testing is trying to eliminate the need for the driver to stop at all. A drive-thru capability uses a suite of sensors to detect the end of the driver s cab and the beginning of the cargo area. Sensing this gap allows the system to 10

11 know when to open the source shutter to begin recording data. An additional capability that required development was a fast-acting shutter, since the original design had a relatively long cycle time with large variance. This design is complete and undergoing life-cycle testing. The combination of end-of-cab sensors and a fast-acting shutter, with appropriate control software updates, means that a drive-thru system is now possible. After automated data acquisition, the system software sends the image to the analysis algorithm. The algorithm determines a result of GREEN (=empty=truck may leave), YELLOW(=software uncertain, operator verify), or RED (=truck not empty, divert for inspection). If the result is green, the truck is allowed to exit with no additional interference. If yellow, the image is sent to the operator s booth for analysis, where the operator may determine that the container is empty and the truck may exit, or that the container requires further inspection and sends the driver to an inspection area. Finally, a red output is automatically sent to the inspection area. Image Analysis Two independent algorithms were developed to automatically analyze the data and determine if a container is empty or not. One algorithm is rule-based and the other relies on statistical methods. The statistical algorithm can learn from operator feedback on uncertain cases. Because the algorithms tend to have different reasons for misidentifying a container, we ultimately hope to create a voting scheme using both algorithms to reduce false alarm rates even further. Currently the algorithms are run independently for testing and characterization. For the remainder of this paper, only the rule-based algorithm will be discussed. A critical first step in the automatic analysis of cargo scans is segmenting the image into various major portions, such as open space, trailer chassis, container floor/walls/roof, and cargo area. This step required a large amount of effort to teach the algorithms about slanted roofs (short trailers have an appreciable angle), walls that are not quite perpendicular, etc. Other real-world effects that had to be accounted for include container patches, tie-down hooks, and other routinely-encountered bits of hardware built-in to the container. Multiple trailer configurations are also common in some areas and the system control logic as well as the image analysis routines had to be programmed to handle them. Results Several sets of experimental tests were conducted to aid in development, to test the sensitivity of the algorithms, and determine accuracy and false alarm rate. By way of example, Figure 8 shows a container image which the algorithm correctly identified as non-empty. Figure 9 shows an image that was a false positive the algorithm identified the container as non-empty when in fact it was empty. 11

12 Figure 8. An accurately identified image showing empty space (purple), chassis and roof (red), cargo area walls (green), and object in cargo area (blue). Note the two container patches along the top edge that are correctly identified as part of the container. Figure 9. A false positive image. The reinforced vertical spars tricked the algorithm into calling this non-empty. The cargo tie-downs were correctly ignored by the algorithm. We tested both algorithms with several thousand test images. The rule-based algorithm achieved an accuracy of 97.2% and false negative rate of 0.4%, while the statistical algorithm reached an accuracy of 96.5% and false negative rate of 2.3%. The false negative rates are considered most important by initial customers, so we are working hard to reduce them. There are still many fertile areas for improving performance and we are confident the false negative rates will continue to drop. VACIS High Resolution System Introduction While the VACIS systems are well-suited to the original goal of narcotics detection, there is opportunity to improve the performance with respect to new priorities such as locating bombs, etc. To this end, one parameter of interest is improved spatial resolution. Fundamental simultaneous design constraints include maintaining or improving system throughput, minimizing the scope of the changes, and, of course, minimizing cost. After analyzing many different possible techniques and detectors to achieve these design goals in the VACIS product line, we have decided to use block detectors, of the type used in nuclear medicine PET studies. This provides a high-resolution option (patent pending) for the VACIS product line. These detectors, with associated image reconstruction software, will enable an improvement in spatial resolution of approximately a factor of three while maintaining throughput. VACIS systems are photon limited by design, so the 12

13 highest resolution will only be achieved with low-attenuation objects. As attenuation increases, it is planned that the software will re-bin the data into larger virtual pixels to achieve a step-wise tradeoff between pixel count density and spatial resolution. Configuration A series of analytic models, ray-tracing code runs, and Monte Carlo code runs indicate that for the VACIS product line, a pixel size of approximately 6 mm is ideal for achieving maximum resolution. Factors that preclude smaller pixels include outscattering from the pixels (effectively reducing contrast), source brightness and scan time. Figure 10. Prototype block detector. 8x8 pixel array is at far end, electronics package at near end, showing DB-15 and RJ-45 connectors. A significant amount of work was performed to design the block detector unit as a nearly self-contained, field replaceable unit (see Figure 10). Integral to the detector housing is the HV power supply, analog preamplifier, ADCs, an FPGA and an embedded microcontroller. The block detector inputs are low-voltage DC power and two master control lines on a single DB-15 connector. The output is an Ethernet data stream on a standard RJ-45 connector. Image Reconstruction The data binning and manipulation required to reconstruct an image at maximum spatial resolution is substantial, and is still a work in progress. The parallax observed by each pixel is significant relative to the pixel size. We have achieved success correcting for this parallax manually by aligning the data for thin objects, and are working on automated techniques to handle complex, thick objects. Results A detector array consisting of up to 20 block detectors is operating on an engineering VACIS unit, providing nearly 130 cm of active imaging height. This prototype array has been used to characterize performance and gather test data. Figure 11 shows an image of a test object scanned with an existing VACIS-II platform and the new detectors. Although this represents the best-case improvement expected, additional testing with thick, dense loads still indicate significant improvement. 13

14 Figure 11. Early data comparing the existing VACIS-II performance (left) with the Next Generation Detector performance (right). The iron wedge target is 51 cm in diameter. This represents the best-case improvement of a high-contrast, thin object in air. Summary and Conclusions The Integrated Container Inspection System (ICIS) comprised of a Portal VACIS, Radiation Portal Monitor (RPM), OCR Automated Container Identification, radioisotope identification, material specific inspection using neutron interrogation and an integrated data display and analysis system shows considerable promise for significantly enhancing capability to detect nuclear weapons and nuclear and other radioactive material in containers. The VACIS and RPM have complementary capabilities since VACIS can detect the attempt to shield a radioactive source using dense materials by imaging the dense material anomaly. The VACIS product line continues to evolve into new applications and to adapt to changing user requirements. The automated empties system provides a commercial platform that will ultimately reduce costs and improve safety and performance at container terminals. The next generation of high-resolution detectors provides significantly enhanced spatial resolution for low-attenuation objects while maintaining system throughput. 14