The Army is intensely interested in tracking and tagging various materials using active emerging and legacy electro-optic systems. This need is incorporated as part of numerous doctrines including Army Capabilities Integration Center (Futures Center) detect enemy activities (supplement 2); detection of chemical, biological, radiological, and nuclear (CBRN) materials at standoff distances (supplement 17); U.S. Army Training and Doctrine Command (TRADOC) Field Manual 525-66 Force Operating Capabilities-02-02 (observe/collect) 02-03 (battlefield operational information); and TRADOC Pamplet 525-3: distributed, networked sensors.

The U.S. Army Engineer Research and Development Center’s (ERDC’s) Topographic Engineering Center (TEC) in Alexandria, VA, is engaged in research to synthesize and model high-quantum-yield luminescent optical reporters based on rare earth constructs that are easily integrated into a variety of sensory taggants and ancillary materials. The study, dubbed “darkfield,” seeks to explore new formularies for quantum tagging materials by developing tunable emitted colors based upon known and unknown basic rare earth chemical transitions. Additionally, this study models the recovery of such materials using both one-off and commercial airborne light/laser detection and ranging (LIDAR) systems serving as the excitation source. Experiments conducted on the emitted luminescence of the materials are validated by several means including a commercial hyperspectral system and night vision observation.

Darkfield research explores the largely hyperspectral imagery (HSI) detection of high-quantum-yield fluorescent labels and their potential use to report CBRN/global war on terrorism (GWOT) targets of interest. The investigation involves the third party illumination of targets with stand-off or airborne laser-induced fluorescence. Over the years, sensing gaps have been identified in hyperspectal imaging spectroscopy making certain targets impossible to confirm. What makes the study unique is the application of commercially available remote-sensing instrumentation to observe an emitted response. Emission and intensity of the fluorescence is measured and recorded using an existing HSI system (calibrated to reflectance) in darkness, hence darkfield. This bistatic or third-party illumination seeks to test a relatively untapped capability of sensitive, high-resolution imaging and nonimaging spectrometers. A modeling approach is used to develop energy flow profiles between each component: target fluorophore, laser illumination/excitation range and power, and hyperspectral sensor-detector. Experiments are designed to test three key hypotheses:

• High-quantum-yield molecular taggants can be chemically tuned and optically modeled to a suitable (laser) excitation source for sensing CBR constituents by hyperspectral sensor in darkfield.
• Environmental efficacy of the taggants in water, soils, and on surface materials can be modeled for input to tailored operational scenarios.
• Recovery of reporter fluorophores can be predicted for a set of variables including laser power, distance, detector/receiving optics, and molecular absorption cross-section of the reporter taggants. Adjustments in excitation source characteristics, taggant molecular composition, or both can improve recovery to achieve target detection confirmation.

Luminescent tags are emerging as a potential value added to current sensing capabilities by virtue of their ability to provide molecular recognition of a threat or by reacting with ancillary constituents in the operational environment. Recent experiments at Fort A.P. Hill, VA, were conducted to match laser power, cross-section, and sensor attributes. In this first year of tests, the SpecTIR hyperspectral scanner was deployed to acquire high-resolution (< .5 meter ground sample distance) night images of an established target farm. The preliminary results show hyperspectral detection for the target and two associated sodium discharge lamps on adjacent fields. These data are still being analyzed and preparations for a follow-on mission are being conducted. We have previously demonstrated the ability to formulate and synthesize luminescent molecular detectors capable of reacting with specific targets. These detectors offer a capability in direct labeling and tagging of CBR threats beyond what is currently able to be measured with reflectance-based hyperspectral sensors alone. Army relevance and payoff is seen in expanded capabilities for existing and emerging multispectral imagery and HSI sensor packages for specific threats. Benefits should also be realized in GWOT and weapons nonproliferation and compliance support.