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Spatial Heterodyne Surface Chemical Agent Detector

SHS CAD

PSI is developing an infrared laser illuminator and spectrometer system for detection and presumptive identification of solids and liquids on surfaces at ranges up to 1 meter. The sensor technology can be configured for handheld operation or on-the-move detection from a vehicle.

The sensor achieves a standoff of 1.2 meters, a depth of focus +/- 25 cm, a spectral resolution of 10 cm-1, a spectral range of 980 cm-1 to 1110 cm-1, and spectrally dependent NER values ranging from 0.1% to 0.5%. The sensor has demonstrated detection down to 30 mg/cm2 for solid simulants (e.g. caffeine, acetaminophen) and explosives (RDX and PETN) on non-porous surfaces, such as roughened aluminum and glass. On porous surfaces such as asphalt, concrete, and sand the sensor architecture has detected TEP with 750 ug/cm2 applied to the surface as droplets with a median mass diameter of 500 microns.

Key Features

Photograph of SHSCAD sensor (left) and in use for proximal surface contaminant detection (right)

The base technology utilizes an infrared laser illuminator and spectrometer system for detection and presumptive identification of solids and liquids on surfaces at ranges up to 1 meter. In particular the system has the following attributes:

Broad QCL spectral coverage: The transmitter design utilizes two Thor Quantum Electronic (TQE) QCL chips that cover 980 to 1200 cm-1 and overlap with the characteristic LWIR vibrational transitions of Chemical Warfare Agents (CWAs) and Non-Traditional Agents (NTAs).
Snapshot spectral acquisition: The SHS acquires all spectral channels across the sensor’s full spectral range with every FPA frame exposure. Coupled with the broad emitting QCL transmitter, the CSD prototype will be capable of acquiring full LWIR ground reflectance spectra at vehicle speeds approaching 40 mph.
Large Depth of Focus (DoF): A boresighted (monostatic) transmitter/receiver configuration results in +/-25 cm DoF, eliminating the need for active focusing of the sensor due to changes in standoff associated with uneven ground terrain.
Interferometer stability: PSI’s rugged SHS interferometer cube design is derived from the JSLSCAD FTIR modulator, but without any moving parts, and has demonstrated excellent thermal stability (0.1 cm-1 spectral shift per °C; stable modulation efficiency)
Physics-based reflectance models: Hardware components are coupled with a detection algorithm that incorporates background spectral clutter and utilizes physics-based reflectance models that capture the phenomenology of chemicals on a surface including homogenous or non-homogeneous films, solid particles, liquid droplets, unknown size distributions, particle fill factors, and areal densities.

Benefit to Warfighter/Customer

The SHSCAD technology being developed enhances chemical sensing capability for the warfighter. Specific end users include chemical reconnaissance units for sensitive sight exploration, chemical decontamination units, and chemical reconnaissance from the Stryker Nuclear Biological Chemical Reconnaissance Vehicle (NBCRV). The system can provide both hand-carried operation and on-the-move, non-contact surface detection and identification of Chemical Warfare Agents, Toxic Industrial Chemicals, and other Non-Traditional Agents.