Rapid analysis of clandestine laboratories is necessary to maintain a protective posture while gaining an understanding of surroundings. We have shown that there is a potential of using a threat anomaly detection (ThreAD) algorithm that allows for rapid, real-time hyperspectral analysis. Understanding if there are primary reagents or products of explosive materials is of concern to recognize what the potential threat in a clandestine laboratory may be. Herein, we discuss the use of a commercial hyperspectral system that is used to collect data that is analyzed using our ThreAD algorithm for existing and emerging explosive threats. In this work, we look at pure spectra of the principle synthetic components of potential explosive threats and the resulting explosive that is made in a method that is consistent with what may be done in a clandestine laboratory. The spectra are parameterized consistent with what is used in the ThreAD algorithm and is clustered in three-dimensional space. The separation of the principle synthetic components and resulting explosives are compared and related to other explosive threats and potential surfaces that the material may reside on. This provides us with the basis of understanding what threats may be detected as anomalies with our ThreAD algorithm and how they compare to others.
Active matter, such as Janus micromotors have been used for applications such as self-assembly, pollution mitigation, and drug delivery. Metal-Organic Framework (MOF)-based Janus micromotors have been recently explored as a method to increase the rate of decontamination for chemical warfare agents in solution due to favorable MOF-chemical interactions. To achieve active-matter decontamination, SiO2@UiO66@Ag MOF-based Janus micromotors were synthesized. In addition to decontamination, the MOF-based micromotors have favorable surface topography for maintaining a localized surface plasmon. This work explores the plasmonic capabilities of Ag@MOF Janus micromotors by systematically changing the amount of Ag, the size of the microparticle that is being used for the plasmonic sensing, and the underlying MOF structure. By changing these parameters, MOF-based micromotors may be able to be used as sensors by utilizing techniques such as Surface Enhanced Raman Spectroscopy (SERS).
Traditional vapor sensing based on vibrational spectroscopy methods employs Fourier-transform infrared (FTIR) spectroscopy, which can produce reliable identification of ppm-level chemical vapors; however, chemical warfare agent poses a threat down to ppb and lower levels. Novel cavity ring-down spectroscopy-based sensors offer a possible path toward combining the high amount of spectral fingerprint data available from traditional IR methods, and the sensitivity of higher-sensitivity technologies, such as nanomaterial arrays and ion-mobility spectroscopy (IMS) which lack high amounts of data which can be used to uniquely identify molecules and are still plagued by high false-alarm rates and low selectivity. Cavity ring-down expands the effective path length of a gas analyzer by orders of magnitude by reflecting the IR light back and forth across an analyzer cavity. By characterizing the loss of light with each bounce by understanding the reflectivity of the mirrors employed at each end of the cavity, a characteristic "ring-down" time of the reflected light through a gas medium can be measured. Then, as analyte is introduced into the cavity, the ring-down times at each wavelength are shifted as a function of the absorbance of the analyte. Comparison of the measured vs. expected ring-down times can be interpreted to produce an IR absorption spectrum of the analyte. The effective pathlength of on order of kilometers allows for extremely high sensitivity beyond the capability of modern FTIR-based analyzers; however, this sensitivity comes at the expense of easier-to-saturate detectors as well. Additionally, cavity ring-down systems have already demonstrated the ability to measure absorption of aerosols both solid and liquid, filling a major gap left by FTIR vapor analyzers and opening the possibility of bioaerosol detection. We present a comparison of the two technologies and where they complement as well as fill in gaps in detection capabilities and offer a path forward for future generations of CB detection.
Raman sensing and mapping techniques traditionally use a tightly focused laser beam to incite and collect Raman scattered photons. A large amount of energy is typically focused in a very small (micron-sized) area potentially resulting in photo-induced damage and can be not eye-safe. In addition, when using a focused-based laser system, scanning a large area is time consuming due to the small area of interrogation and must be done at a specific distance. Therefore, either prior knowledge of the sample location (in three dimensions) is necessary, or a smaller area must be scanned. In this work, we demonstrate a hand-held proximal Raman detection instrument that uses a non-focused laser beam to interrogate a larger area. This reduces the time it takes to map a surface and provides greater flexibility in targeting the area to interrogate. Herein, we show detection and mapping of explosives in two dimensions with this hand-held proximal Raman instrument as well distance dependence of this non-focused instrument with explosive materials.
Real-time analysis of data provides input for decision makers. However, in the battlefield, that could be the difference between life and death. Therefore, techniques must be developed that provide data in a way that can be reduced to real-time information. Hyperspectral data is often sought after as it provides spatial-spectral information but comes with a large computation cost. Real-time analysis of hyperspectral data is often difficult after an appreciable amount of time due to the volume of data that must be analyzed. However, commercial off-the-shelf instrumentation that normally outputs large hypercubes of information can be computationally managed in a way such that real-time processing is achievable at low levels of analyte. In this work, we show near-trace level anomaly detection of explosive precursors, explosives, and pharmaceutical surrogates on real-world surfaces using a commercial off-the-shelf instrument. The threat anomaly detection (ThreAD) algorithm that is employed uses a semi-supervised machine learning method to determine where the anomalous data (i.e. analyte) is present. This work will provide approximate limits of anomaly detection (LOADs) for some analyte/surface combinations in laboratory conditions.
The accidental release of industrial and agricultural chemicals can pose a serious threat to life and the environment. Therefore, researchers have been exploring detection methods of commonly transported chemicals in order to minimize potential harm or destruction in response to an accidental release. One method is to use a network of commercial sensors to track a chemical spill but with each sensor costing upwards of $600, this type of network can become prohibitively expensive and may not be practical for real world use. Specifically, we aimed to develop a network of custom electrical conductivity sensors with each sensor made from an inexpensive Arduino board showing comparable detection results while costing an order of magnitude less. In our experiments, the network of sensors covered 83 in2 in a container filled with different types of water (e.g. deionized, melted snow, sea, river, and tap). The network of custom sensors showed high ammonia concentrations near the release point of an initial laboratory scale ammonia release with low ammonia concentrations away from the release point. As equilibrium was reached, the sensors showed the same ammonia reading. Additionally, a 2-D map was made to track the simulated ammonia spill overtime. Overall, this works shows that this network of custom Arduino sensors can be used to map the detection of accidental ammonia release as an inexpensive replacement for the commercial sensors, which will promote accessibility of future testing for the broader community.
Artificial illumination is required for a line scanning passive hyperspectral spectrometer when operating a system of this type in non-daylight conditions. While in general more photons will yield a larger reflectance signal return to the sensor, a source that outputs a large number of photons is unlikely to be compatible with a compact hyperspectral spectrometer on a small aircraft or using in a handheld manner. Therefore, in this paper we investigate a small tungsten halogen source coupled with off-the-shelf optics to create a compact artificial illumination source to provide photons for the spectrometer. After characterizing the compact halogen source and comparing its output characteristics to larger sources currently in use, several optical trains were designed to focus the sources output to the instruments’ field-of-view. The results detailed herein show that a compact source can allow for a hyperspectral spectrometer to operate with a compact artificial illumination source with a minimal decrease in performance.
Understanding a system’s performance while operating under different scenarios is difficult because of the vast number of varying parameters that need to be accounted for. To mitigate some of the difficulty a model can be developed that provides some predictability in a system’s performance thereby reducing material usage and laboratory time. It is therefore prudent to understand these parameters and capture that information in order to increase the predictability of a system, especially prior fielding. Through modeling, we connect laboratory scale data with potential scenarios in the field to accomplish this. In this paper, we show that through the modeling of a combination of spectra and instrument operating characteristics we can provide a predictive capability of a system’s performance. Our anomaly detection algorithm can predict a limit of anomaly detection (LOAD) for potential scenarios and then compare them to actual data for validation of our predictive capability. We show similar LOADs in both simulation and actual data collected. We further develop our model to account for realistic field scenarios and evaluate changes in performance.
Building on our previous development of a compact, portable, and low SWaP gas analyzer (11” x 6.7” x 5.1”, 7.8 lbs) based on photoacoustic spectroscopy and using broadband quantum cascade laser arrays, we demonstrate here compositional analysis of airborne aerosols using this instrument. With an integration time of 330-ms per laser, and ~70 seconds for a spectrum covering 950-1500 cm-1, our instrument showed a detection sensitivity at the mg/m3 level for solid and liquid-loaded solid aerosols. Additionally, Malathion-loaded aerosols can be discriminated from pure Syloid aerosols based on their absorption features. The preliminary results show a potential path for developments of a portable real-time aerosol composition analyzer.
The detection of bulk materials is well-understood and many transduction methodologies exist. In contrast the detection of distributed or dispersed materials is still under study due the unique sequence of events under which this this occurs. For dispersed materials the problem is twofold, first you need to intercept or sample a location containing an analyte of interest and second you must be able to detect and identify that analyte. In addition, intercepting or sampling from sparsely contaminated areas is a more difficult problem as there is more background clutter due to less analyte available for interrogation and identification. Potential dispersed threats may include IED residues or disseminated materials dispersed in order contaminate an area with harmful chemicals. Using technologies such as Raman spectroscopy can provide real-time unique chemical-specific information to detect dispersed materials. However, understanding adequate sampling methods based on the instrument physical operation characteristics can help reduce false negatives and improve maneuverability through contested areas by bounding operational limitations. Since disseminated materials are deposited on a surfaces in a log-Normal fashion, the deposition pattern can be modeled and the potential ability to detect can be determined by understanding the probability of intercept of an analyte by the sampling method., i.e., for Raman the potential of a focused laser to illuminate an analyte containing location. The operating characteristics in question are the area of interrogation, repetition rate of the sampling method, and the speed at which the sampling is completed. In this paper, deposition patterns are modeled, and a CW Raman instrument is used to determine probability of intercept for several area-based concentrations, at different speeds, and with different interrogation areas. The data is analyzed based on both a predicted model and actual data. Determining and understanding these operating characteristics will aid in understanding of the necessary sampling, i.e., laser intercept, in order to provide desired confidence levels for detection.
The inherent wealth of information associated with hyperspectral data provides a data stream that could be leveraged for situational awareness or providing immediate user feedback. However, the enormous amount of data that is produced by some system’s data stream requires longer processing times and often post-processing techniques. Therefore, it is prudent to develop real-time hyperspectral processing techniques that are capable of operating at maneuver speeds. Anomaly detection techniques applied to higher order statistics of the hyperspectral data can provide immediate user feedback for awareness. Determining capabilities prior to applying directly to a system is also informative and provides an in silico point of reference. In this paper, we show, through the use of a real-time simulator (RTS) in the MATLAB environment, a method for simulating the processing speed of a data stream based on how data is received from the instrument. In this work, the RTS provides sub 100ms capabilities based on non-optimized code within the MATLAB environment and is largely limited by the write speed in MATLAB. Utilizing virtual memory and the flexibility of MATLAB allows for simulating real-time capabilities of already obtained hyperspectral data prior to implementing it on a device. Additionally, applying the algorithm to a simulated ground truth data provides a theoretical limit of anomaly detection (LOAD). We further compare theoretical LOADs with actual anomaly detection capabilities in a laboratory environment.
KEYWORDS: Statistical analysis, Scanners, Data processing, Signal to noise ratio, Imaging spectroscopy, Hyperspectral imaging, Stochastic processes, Detection and tracking algorithms, Photonics, Line scan image sensors
Hyperspectral imaging (HSI) has become increasingly popular for sensing in defense, commercial, and academic research for its ability to acquire vast amounts of information, relatively quickly, at stand-off distances. As such, the need for rapid or near-real time data reduction is becoming more evident especially when immediate knowledge of the area under investigation is required such as in contested areas, the scene of natural disasters, and other similar scenarios. While analysis of the underlying spectral information may provide specific information about materials present, in HSI determining an anomaly can be just as informative in scenarios such as CB detection for avoidance. Therefore, a rapid, real-time HSI anomaly detection algorithm is merited. In this paper, we present work towards an algorithm for near-real time anomaly detection utilizing higher-order statistics and, in particular, implications due to changes in skewness and kurtosis, the 3rd and 4th central moments. We demonstrate using a visible-SWIR hyperspectral line scanner that anomalies (thiodiglycol and acetaminophen) can be detected in data that is updated to simulate real-time analysis. Changing spectral features result in changes in the probability density function, and can be specifically realized with comparisons of higher order statistics (i.e. skewness and kurtosis), thereby reducing a full spectral analysis at each voxel to a comparison of two values at each pixel. This paper explores utilizing this concept as a means for anomaly detection, evaluating different surfaces that an analyte may be present on, and lastly presents work towards automated background updates for anomaly detection on dynamic surfaces.
Super resolution chemical imaging can provide high spatial resolution images that contain chemically specific information. Additionally, using a technique such as Raman scattering provides molecular specific information based on the inherent vibrations within the analyte of interest. In this work, commercially available fiber bundle arrays (1mm diameter) consisting of 30,000 individual fiber elements (4μm diameter) that are then modified to obtain surface enhanced Raman scatter are employed. This allows for the visualization of vibrational information with high spatial (i.e. sub-diffraction limited) resolution over the 30,000 individual points of interrogation covering a total imaging diameter of approximately 20μm in a non-scanning format. Using these bundles, it has been shown that dithering can increase the spatial resolution of the arrays further by obtaining several sub-element shifted images. To retain the spatial resolution of such images, cross talk associated with these tpared bundles must be kept at a negligible level.
In this paper, a study of luminescent particles isolated in individual fiber wells has been performed to characterize the cross talk associated with these fiber bundles. Scanning-electron microscope (SEM) images provide nanometric characterization of the fiber array, while luminescent signals allow for the quantitation of cross talk between adjacent fiber elements. From these studies negligible cross-talk associated with both untapered and tapered bundles was found to exist.
This review describes the recent advances in plasmonic nanostructures for various sensing applications. In particular, significant advances in surface-enhanced Raman, surface plasmon resonance, and metal-enhanced fluorescence-sensing methodologies associated with the introduction of plasmonic nanostructures, made over the past decade, are highlighted. Plasmonic properties of the various nanostructures employed for each sensing technique are also tabulated to provide a systematic overview of the state-of-the-art in each sensing field. This review is not intended to be a comprehensive compilation of the literature but rather a critical review of the recent significant advances in plasmonic nanostructures for each sensing regime.
Super-resolution chemical imaging via Raman spectroscopy provides a significant ability to simultaneously or pseudosimultaneously monitor numerous label-free analytes while elucidating their spatial distribution on the surface of the sample. However, spontaneous Raman is an inherently weak phenomenon making trace detection and thus superresolution imaging extremely difficult, if not impossible. To circumvent this and allow for trace detection of the few chemical species present in any sub-diffraction limited resolution element of an image, we have developed a surface enhanced Raman scattering (SERS) coherent fiber-optic imaging bundle probe consisting of 30,000 individual fiber elements. When the probes are tapered, etched and coated with metal, they provide circular Raman chemical images of a sample with a field of view of approximately 20μm (i.e. diameter) via the array of 30,000 individual 50 nm fiber elements. An acousto-optic tunable filter is used to rapidly scan or select discrete frequencies for multi- or hyperspectral analysis. Although the 50nm fiber element dimensions of this probe inherently provide spatial resolutions of approximately 100nm, further increases in the spatial resolution can be achieved by using a rapid dithering process. Using this process, additional images are obtained one-half fiber diameter translations in the x- and y- planes. A piezostage drives the movement, providing the accurate and reproducible shifts required for dithering. Optimal probability algorithms are then used to deconvolute the related images producing a final image with a three-fold increase in spatial resolution. This paper describes super-resolution chemical imaging using these probes and the dithering method as well as its potential applications in label-free imaging of lipid rafts and other applications within biology and forensics.
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