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Joint Services Lightweight Standoff Chemical Agent Detector (JSLSCAD)

The JSLSCAD is a passive infrared (IR) detection system that detects the presence or absence of chemical warfare agents in the 800 to 1200 wave number region of the electromagnetic spectrum by monitoring the ambient background IR radiation. The JSLSCAD signal processing hardware discriminates between the chemical targets and the other nontoxic species in a complex battlefield environment.

The Joint Service Lightweight Standoff Chemical Agent Detector is a small, fully-automatic, standoff chemical agent detector. The unit is capable of on-the-move, real-time detection from either aerial or surface platforms. The unit will detect and alarm to a chemical agent cloud up to 5 kilometers away. The detector also provides chemical identification information and data for activation of countermeasures to avoid contamination. The JSLSCAD is equipped for visual and audible alarm and can display the agent class and relative position. This information is available locally and transmission to battlefield information networks. JSLSCAD also has the capability to indicate an all-clear condition.

The problem of detecting chemical vapors in the atmosphere has been of interest to the military for several decades. It is well known that chemical warfare (CW) agents such as Mustard (H-agents), Lewisite, VX and the nerve gases (G-agents) have strong absorption features in the long-wave infrared (LWIR, 8-12 mm) region of the spectrum. Standoff detectors address the requirement to detect vapor clouds produced by agent releases. Methods of delivery include shells, bombs, bomblets, missiles and sprayers, generating clouds as large as 100 meters wide. Given sufficient thermal contrast between the vapor cloud and the background, it is possible to detect and identify a CW agent by remote sensing spectrometry.

The M21 Automatic Chemical Agent Alarm, first used during Operation Desert Storm, is the first standoff chemical agent detector approved for use by the soldier. It is currently used by the Army and Marine Corps to provide contamination avoidance against chemical agent vapor threats at up to 5 km range over a 60 degree arc. The sensor is a (non-imaging) Fourier-transform infrared (FTIR) spectrometer that operates in the 8-12 mm atmospheric window at 4 cm-1 spectral resolution (1cm-1 is approximately 10 nm at 10 mm). The M21 is due to be replaced by the smaller, more capable Joint Services Lightweight Standoff Chemical Agent Detector (JS-LSCAD), which is currently in advanced engineering development.

The next generation of passive standoff chemical agent detector is being conceived as an imaging device. The advantages of such a system over the current generation systems include inherent background measurements (through the multiple fields of view provided by the imaging capability), cloud mapping capability and lower false alarm rate. By correctly exploiting the added spatial information we can increase the probability of detection (and consequently reduce the probability of false alarms).

The sensor data processing techniques depend on what information is needed. For the M21 and JS-LSCAD, the information required is detection and identification of CW agents. This limited requirement obviates the need for strict radiometric calibration, since vapors can be detected and identified by their spectral shape. During the initial development of the M21, detection algorithms based on direct interferogram processing were used in order to eliminate the need to calculate a Fourier transform. With the massive improvement of digital signal processing (DSP) technology, this approach is no longer necessary. Currently, data processing for the M21 involves several pre-processing steps to remove the phase misalignment, instrument self-radiance and background clutter. Unlike the M21, the JS-LSCAD is required to operate on the move, so background clutter suppression can not be accomplished by subtracting a background spectrum. A technique based on Super-Clip Apodization has been shown to reduce the background clutter relative to the chemical signal.

The target chemical "scoring" for the M21 is done by using software spectral filters. Two filters are used for each target: one optimized for terrain background and another for low-angle sky. The filter coefficients are obtained by a non-parametric training method which uses a large number of training samples. The coefficients are adjusted so that a positive score indicates the presence of the target chemical. The alarm is triggered by certain sequences of positive results.

The next generation of processing techniques will include adaptive spectral filtering for initial detection, quantitative transmittance retrieval for cloud optical depth estimation, cloud ranging and methods for analyzing data with unknown chemical species. Adaptive spectral filtering is an improvement upon the technique currently used. It takes advantage of the added spatial dimension provided by imaging spectrometers by computing local statistics in order to mitigate the effects of interferences. For example, the Constrained Energy Minimization (CEM) technique can be modified to compute a local spectral correlation matrix. This allows the spectral filter to adapt to both gradual and sudden changes in the scene statistics. An important issue with implementation of adaptive filtering is computational load. For example, CEM requires the stable inversion of the spectral correlation matrix in real-time. This is a challenge for most single-processor computers, but parallelization can provide the necessary performance.

JSLSCAD consists of four major components: scanner module, sensor electronics module, operator display unit, and power adapter. There are two configurations of the scanner module. The aerial applications scanner covers a 60-degree forward-looking cone and ground mobile, fixed-site, and shipboard configurations scan 360-degrees in azimuth and +50 to -10-degrees in elevation. The mobile configurations of JSLSCAD Block I will be used on platforms such as ground vehicles and ships. Aircraft configurations will be included in JSLSCAD Block II. The JSLSCAD Block I is intended to be integrated into the Joint Service Light Nuclear, Biological, and Chemical (NBC) Reconnaissance System (JSLNBCRS) and the Stryker-NBC Reconnaissance Vehicle, and will be employed at fixed sites such as air bases and aboard Navy landing ship docks (or equivalent aviation capable amphibious ships). JSLSCAD Block II is intended to be carried on Army and Navy helicopters, and outboard on selected Air Force C-130 aircraft. Present plans call for the JSLSCAD to be carried as an unmanned aerial vehicle payload, but the unmanned aerial vehicle to be used has not been selected.

The Joint Program Office for Chemical, Biological, Radiological, and Nuclear Defense approved the current operational requirements document in July 2003. JSLSCAD achieved Milestone II on September 17, 1996. The Test and Evaluation Master Plan (TEMP) for JSLSCAD was approved in 1997, before the system came under DOT&E oversight in January 2000. In August 2003, the Joint Program Executive Office for Chemical and Biological Defense decided to restructure the program, which required a revised TEMP.



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Page last modified: 07-07-2011 02:44:02 ZULU