Functional principle of the laser-based standoff detection of hazardous substances
The premeditated as well as the unintentional release of chemical, biological, radioactive, nuclear or explosive (CBRNE) substances poses a threat to national security as well as to personal safety. There is also an increasingly important security aspect as with respect to soldiers, deployed to crises regions like actually Afghanistan, who are more and more endangered by terroristic attacks. Numerous nationally (BMBF) and internationally (EU-FP7, EDA) funded research programs give evidence for the urgent needs of reliable detection methods. The laser-based standoff detection represents a promising option for the early detection, recognition and identification of hazardous substances at a safe distance in good time. Appropriate countermeasures can be initiated at an early state and potential risks for the population and the first responders can be reduced.
The identification of hazardous substances becomes difficult by their diversity. In addition, different ways of spread, contamination and incubation increase the complexity of the problem. Chemical substances, like e.g. the neurotoxin Sarin, are mainly widespread through the air in their gas phase. Bacteria and viruses can adhere to surfaces or are spread into the air in the form of aerosols. Airborne biological substances have lifetimes of several days up to several weeks.
Many of the presently available, conservative detection methods need direct contact to the agent. This requirement impedes the early detection of the hazardous substance and may be dangerous for the operators. Other solutions allow detection distances to the contaminant only in the meter range (portal systems) or show a strong dependence on the background radiation.
The laser-based detection methods make use of various interaction mechanisms between electromagnetic radiation and matter. In this process, a large number of substances in different states of matter can be detected up to the kilometre range.
The demands for a genuine standoff detection are given by realistic threat scenarios and the attendant environmental conditions. Laser-based standoff detection is prepared to be operated at busy places inside and outside of buildings depending on the specific hazardous situation. Any risks of the system itself have to be excluded. The laser performance is chosen in the eye-safe range. The corresponding laser wavelength has to allow for an efficient interaction with the unknown agent, preserve the eye-safety and fit within the spectral ranges of sufficient atmospheric transmission. Further environmental influences are a variable background radiation, the limitation of the optical range by unfavourable weather conditions, smog or clouds of dust, or the presence of confusors, as agent-alike trace substances.
The stated objective of the R&D projects is the design of a compact and mobile overall laser-based standoff system allowing for a fast and efficient deployment in hazardous situations.