Arthur H. Carrieri

Neural network pattern recognition by means of differential absorption Mueller matrix spectroscopy

Artificial neural network systems were built for detecting amino acids, sugars, and other solid organic matter by pattern recognition of their polarized light scattering signatures in the form of a Mueller matrix. Backward-error propagation and adaptive gradient descent methods perform network training. The product of the training is a weight matrix that, when applied as a filter, discerns the presence of the analytes on the basis of their cued susceptive Mueller matrix difference elements. This filter function can be implemented as a software or a hardware module to a future differential absorption Mueller matrix spectrometer.

Differential absorption Mueller matrix spectroscopy and the infrared detection of crystalline organics

The complete 16-element Mueller matrices for backscattering from amino acids, sugars, and other enantiomorphic compounds pressed into wafer form were measured at infrared wavelengths. For each compound a pair of CO(2) laser lines was selected from the 9.1-11.6-mum region such that one line excited an absorption band in the compound, whereas the other did not. It was observed that at least some of the matrix elements differed significantly depending on which of the two wavelengths was used in the measurement. We propose that a neural network pattern recognition system can be trained to detect the presence of specific compounds based on multiwavelength backscatter Mueller matrix measurements.

Identification of contaminant coatings over rough surfaces using polarized infrared scattering

An optical technique to identify the presence of chemical coatings over rough surfaces is described. It is based on the selective use of elements of the 4 x 4 Mueller matrix. The full-wave theory of electromagnetic scattering is used to predict six independent Mueller elements from randomly rough uncoated (dry) and coated (wet) surface materials as functions of the media complex dielectric coefficients, backscattering angle, and midinfrared wavelengths of laser-beam excitations that are polarization modulated. The set of independent elements at beam wavelengths and backscattering angles [M(mn) (lambda(i), lambda(i))] most sensitive to i optically thick contaminant coatings are statistically obtained from the full-wave database, and detection-parameter sets [lambda(i), lambda(i)] are inputs to another algorithm designed to identify the contaminant coating (when present and interacted by the irradiating beams). These algorithms facilitate the operation of a multi-CO(2) laser-ellipsometer facility now under development at the U.S. Army Chemical Research, Development, and Engineering Center for the remote detection of chemical or biological surface contaminants.

Infrared detection of liquids on terrestrial surfaces by CO 2 laser heating

The strong mid-infrared bands of contaminant liquids wetting sand and soil can be remotely detected by 0.103-eV laser irradiation with beam intensity well below that which chars the terrain. Emissions from heated nonvolatile interstitial liquid layers and extinction of thermoluminescence by beam-generated vapors of volatile contaminants are spectrally distinct within the infrared contaminant fingerprint spectral region-as measured by a Michelson interferometer based FT-IR radiometer instrument. The contaminants vibrational resonance intensities change proportionally in magnitude and sign in measured contiguous difference FFT spectra, within a specific beam-to-sample dwell period. The onset irradiation time and period for detecting these bands can differ according to amount and volatility of contaminant, beam intensity and its time of dwell necessary to produce sufficient thermoluminescence flux, and on the quantity of interferogram data acquisitions.

Photopolarimetric lidar dual-beam switching device and Mueller matrix standoff detection method

We present an optomechanical switching device (OSD) for a photopolarimetric lidar system with differential-absorption Mueller matrix spectroscopy standoff detection method. An output train of alternate continuous-wave CO2 laser beams [...L1:L2...] is directed onto suspect chemical-biological (CB) aerosol plume or the land mass it contaminates (S) vis-à-vis the OSD, where L1 [L2] is tuned on [detuned off] a resonant molecular absorption moiety of CB analyte. Moreover, both incident beams and their backscattered radiances, from S, are polarization-modulated synchronously so as to produce gated temporal voltage waveforms called scattergrams recorded on focus at the receiver end of polarization lidar sensor system. All 16 elements of the Mueller matrix (Mij) of S are measured via digital or analog filtration of constituent frequency components in these running scattergram data streams (phase-sensitive detection). A collective set of normalized differential elements {ΔMi,j} (ratioed to element M11) that are susceptible to the analyte, probed on-then-off its molecular absorption band, form a unique detection domain that is scrutinized. Any mapping onto this domain in Mueller-space, from incoming sensor scattergram data sets preprocessed by algorithm and forwarded through a trained neural network pattern recognition system, cues a standoff detection event.

Chemical imaging sensor and laser beacon

Design and functional aspects of PANSPEC, a panoramic-imaging chemical vapor sensor (PANSPEC is an abbreviation for infrared panoramic-viewing spectroradiometer), were advanced and its optical system reoptimized accordingly. The PANSPEC model unites camera and fused solid-state interferometer and photopolarimeter subsystems. The camera is an eye of the open atmosphere that collects, collimates, and images ambient infrared radiance from a panoramic field of view (FOV). The passive interferometer rapidly measures an infrared-absorbing (or infrared-emitting) chemical cloud traversing the FOV by means of molecular vibrational spectroscopy. The active photopolarimeter system provides a laser beam beacon. This beam carries identification (feature spectra measured by the interferometer) and heading (detector pixels disclosing these feature spectra) information on the hazardous cloud through a binary encryption of Mueller matrix elements. Interferometer and photopolarimeter share a common configuration of photoelastic modulation optics. PANSPEC was optimized for minimum aberrations and maximum resolution of image. The optimized design was evaluated for tolerances in the shaping and mounting of the optical system, stray light, and ghost images at the focal plane given a modulation transfer function metric.

Thermal luminescence sensor for ground-path contamination detection

A standoff method of detecting liquids on terrestrial and synthetic landscapes is presented. The interstitial liquid layers are identified through their unique molecular vibration modes in the 7.14-14.29-microm middle infrared (fingerprint) region of liberated thermal luminescence. Several seconds of 2.45-GHz beam exposure at 1.5 W cm(-1) is sufficient for detecting polydimethyl siloxane lightly wetting the soil through its fundamental Si-CH3 and Si-O-Si stretching modes in the fingerprint region. A detection window of thermal opportunity opens as the surface attains maximum thermal gradient following irradiation by the microwave beam. The contaminant is revealed inside this window by means of a simple difference-spectrum measurement. Our goal is to reduce the time needed for optimum detection of the contaminants thermal spectrum to a subsecond exposure from a limited intensity beam.

Panoramic infrared-imaging spectroradiometer model with reverse phase-modulated beam broadcasting

The optical design of a passive remote sensor, a panoramic spectroradiometer (PANSPEC), and its computer-simulated image performance are presented. PANSPEC monitors the surrounding infrared environment for chemical clouds, detecting a presence once absorption or emission spectra characteristic of the chemical species are resolved. PANSPEC broadcasts chemical presence and cloud heading when equipped with a laser transmitter that projects a polarized laser beam source with phase encryption back through the optical system into object space. Various merit functions were programmed and accessed during computer optimization runs for shaping and positioning of the instruments semishell entrance window, collector, collimator, interferometer, and imager. The result is a balanced near-diffraction-limited circular image, 6.3 mm across with 10-line pairs/mm spatial resolution at 50% modulation, and an f/2.3 working speed.

Computation, visualization, and animation of infrared Mueller matrix elements by scattering from surfaces that are absorbing and randomly rough

Computation of Mueller matrix elements by infrared scattering from randomly rough two-dimensional surfaces and results of a method for graphic display of the data are presented. A full wave electromagnetic scattering model first generates raw data elements of the 4 × 4 Mueller matrix F(θ, nλ, kλ, σs(2), ?h(2)?) in beam backscattering angle (θ) ranging from normal to oblique incidence, in refractive index of the beam scatterer (nλ - ikλ) spanning the 9 ≤ λ ≤ 12.5 µm midinfrared band, and in mean-squared slope ((σS(2)) and mean-squared height (?h(2)?) of the scattering surface. These data are next compressed into a graphics format file occupying considerably less computer storage space and mapped into color images of the Mueller elements as viewed on a high-resolution graphics terminal. The diagonal and two off-diagonal elements are animated in the λ-θ plane according to varitions in σs(2) and ?h(2)?. Predicted elements for polarized IR beam energies on vibrational resonance of the surface molecules, and particularly the off-diagonal elements, show subtle properties of the scatterer as viewed in the animation sequences.

Full Wave Solutions for Mueller Matrix Elements Used to Remotely Sense Irregular Stratified Structures

Full wave solutions for electromagnetic waves scattered from an irregular stratified structure consisting of three distinct media are used to compute the backscatter Mueller (phase) matrix elements. The Mueller matrix provides a complete polarimetrec characterization of the scattered radiation from the layered structure. Illustrative examples of the six independent backscatter Mueller matrix elements are presented as functions of incident angle for isotropic random rough surfaces with different roughness parameters. The exication is in the mid infared band. These theoretically predicted matrix elements can be used to facilitate the selection of the optimum backscatter angle and wavelength to remotely detect the presence or absence of liquid coatings over rough terrain. When a coating material is identified, it is also necessary to determine the amount of liquid coating (per unit beam cross section area) deposited onto the terrain.