Georgia Tech is in the second year of a Multi-University Research Initiative designed to study the impact of environmental processes on optical signatures. In particular, this program is conducting phenomenological studies on hyperspectral and polarimetric signatures of various target classes in the visible and infrared wavebands. Initial research studies have focused on landmines and the impact of various environmental factors and processes (e.g., subsurface processes) on the resultant spectral infrared signatures. A variety of approaches have been employed in this research to gain a better understanding of the impact of the environment on the spectral and polarimetric characteristics of soil and landmine signatures. These approaches include theoretical analyses, physics-based signature modeling, field measurements, and laboratory studies. Results from these studies will be presented that underscore the importance of incorporating the subsurface processes into the signature analyses. The results of these analyses have been propagated to algorithm developers to permit the creation of more robust processing techniques based on these physical analyses and models. This paper will present an overview of the program, a review of the research investigations initiated over the past year, and a summary of the results from these initial investigations.
Attenuated total reflection (ATR) spectroscopy is a well established optical technique investigating fundamental molecular vibrations in the mid-infrared (MIR) spectral regime for a wide variety of samples including liquids, thin films and powders. In the present study, first results simulating the influence of weathering processes on the spectral characteristics of soils are discussed. In particular, the effect of wetting and drying cycles on IR spectra of fine quartz (SiO2) powders has been investigated with ATR techniques. Resulting from a wetting and drying cycle, the sample spectra of quartz powders revealed significantly increased absorption intensities throughout the spectral region of interest (1400-600 cm-1). We hypothesize that this effect results from a higher packing density of the particles following the wetting procedure with the fines packed into interstitial spaces closer to the ATR waveguide surface. Moreover, a strong red shift of approx. 40 cm-1 of the absorption band assigned to asymmetric SiO4 stretching vibrations (1050 cm-1 to 1250 cm-1) could be observed. Both effects, increase in intensity and spectral shift, are reversed by mechanically disturbing the cemented powder after the wetting/drying cycle. Experiments with s- and p-polarized infrared radiation show similar (reversible) spectral shifts for this particular frequency range. It is expected that these findings will lead to better understanding of the spectral characteristics of soil in the mid-infrared spectral domain providing improved interpretation of data retrieved from disturbed soils e.g. potential landmine sites during hyperspectral imaging.
This paper presents preliminary results of an investigation into the impact of buried objects on the environmental properties and electro-optical spectral characteristics of terrain features. This study focused on the analyses of various sensor information, including hyperspectral and thermal data, collected under a limited set of circumstances; these analyses include laboratory measurements and theoretical computations. A digital terrain model incorporating the relevant physical processes was also constructed to support these investigations. These analyses are particularly relevant to the detection of landmines and the exploitation of hyperspectral sensor data in this application. Results from these analysis efforts will be presented along with example spectral data and computational results.
The emerging demands of marine monitoring have initiated increased efforts to develop sensor systems capable of screening organic pollutants in seawater. The construction of a sensor system based on a Fourier transform infrared (FT-IR) spectrometer coupled to a mid-infrared fiber-optic sensor head to be used in a tow-body for underwater applications is part of the European Union project "SOFIE — Spectroscopy using Optical Fibers in the Marine Environment", aiming at the introduction of an entirely optical approach for in-situ ocean monitoring. The investigated analytes of this initiative include heavy metals, chlorinated hydrocarbons and aromatic hydrocarbons, which will be addressed using fiber-optic sensing schemes based on absorption (mid-infrared fiber-optic evanescent wave spectroscopy (MIR-FEWS), fluorescence, surface enhanced Raman scattering (SERS) and refractivity (surface plasmon resonance (SPR)). Since the system is modular, adaptation of existing techniques or the incorporation of new modules ensures the detection of further analytes. As part of this research project, a compact FT-JR based sensor system has been developed, reconstructing a Bruker Vector 22 FT-JR spectrometer. For the first time, a spectrometer was redesigned to fit into a submersible tube, with an inner diameter of 270 mm and an overall length of 1 100 mm. This approach proved capable of multi-component analysis in seawater, demonstrated for the example of various chlorinated hydrocarbons, as well as relatively low susceptibility to interfering parameters such as salinity and turbidity. First successful field test of the system integrated in a remotely operated vehicle corroborate the feasibility of this approach. With respect to the technological perspectives using miniaturized sensor components, a notable impact on this novel application area for MIR sensors can be expected.