Infrared differential-absorption Mueller matrix spectroscopy and neural network-based data fusion for biological aerosol standoff detection

Abstract

An active spectrophotopolarimeter sensor and support system were developed for a military/civilian defense feasibility study concerning the identification and standoff detection of biological aerosols. Plumes of warfare agent surrogates gamma-irradiated Bacillus subtilis and chicken egg white albumen (analytes), Arizona road dust (terrestrial interferent), water mist (atmospheric interferent), and talcum powders (experiment controls) were dispersed inside windowless chambers and interrogated by multiple CO(2) laser beams spanning 9.1-12.0 microm wavelengths (lambda). Molecular vibration and vibration-rotation activities by the subject analyte are fundamentally strong within this "fingerprint" middle infrared spectral region. Distinct polarization-modulations of incident irradiance and backscatter radiance of tuned beams generate the Mueller matrix (M) of subject aerosol. Strings of all 15 normalized elements {M(ij)(lambda)/M(11)(lambda)}, which completely describe physical and geometric attributes of the aerosol particles, are input fields for training hybrid Kohonen self-organizing map feed-forward artificial neural networks (ANNs). The properly trained and validated ANN model performs pattern recognition and type-classification tasks via internal mappings. A typical ANN that mathematically clusters analyte, interferent, and control aerosols with nil overlap of species is illustrated, including sensitivity analysis of performance.

Thermal luminescence spectroscopy chemical imaging sensor

“…Clustering is the sole requirement of CWA standoff detection-an extraordinary capability for detecting both known and unknown analytes. Developing unsupervised SOM ANN pattern recognition systems for a PSCSMbased prototype system will build on our experiences of integrating SOM technology to a laboratory MIR differential-absorption Mueller matrix polarized light scattering sensor, which solved the bioaerosol standoff detection problem [8].…”

Polarization signatures of airborne particulates

“…A few experimental studies aimed at measuring the polarization state of scattered light from particulate matter (PM) species have been done but they are mostly limited to discrete wavelengths in the visible and infrared (IR) regions; emission lines between 9.1 and 12.1 μm from a CO 2 laser. 2 Spectral measurements of polarization properties of such samples over a broad wavelength region and at a high spectral resolution are scarce, primarily due to lack of available instrumentation.…”

Visibility measurement using multi-angle forward scattering by liquid droplets

“…In the atmosphere, there are many fluorescence-based bio-aerosol detectors that utilize a single UV wavelength source to excite fluorescence from aerosol particles [1][2][3][4]; in addition, white light [5,6], infrared spectra [7][8][9], polarization nephelometer [10] and lidar [11,12] are also used to measure optical properties of aerosols. Many particle properties have been studied, including particle size [13][14][15], particle number [16,17], mass concentration [18], irregularly shaped particles [19], particle velocimeter [20], a particle over two angulardimensions [21], randomly shaped particles [22], particle extinction [23] and scattering phase [24,25].…”