Sensor Systems for Biological Agent Attacks Protecting Buildings and Military Bases (2005) / Chapter Skim
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5 Point and Standoff Detection Technologies
5 Point and Standoff Detection Technologies
Pages 71-83
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From page 71... ...
For this reason, detection at or near the point and time of release offers the best opportunity for distinguishing a potential biological agent attack from fluctuations in the natural background. Simulant tests and modeling results using a nominal density of biological agents of 1 ok organisms per gram demonstrate that a concentration of 1,000 particles per liter or greater will remain in the vicinity of a biological agent release with a source term of approximately 1 kilogram for 5 to 20 minutes 2 The actual times are extremely dependent on wind speed and proper formulation of agent.
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From page 72... ...
This chapter examines the current state of the art of both point and standoff detection technologies. POINT DETECTION TECHNOLOGIES Nonspecific spectroscopic point detectors typically consist of a particle collection and concentration system, a laser light source, and appropriate electronics for detemmination of the size, shape, and spectral signature of aerosol particles.
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From page 73... ...
Although the acquisition of particle size and shape information is rapid, these systems do not provide infommation about flhe biological nature of the detected particles. Cur rent instrumentation Researchers at MlT's Lincoln Laboratory are currently funded for the development and field-testing of the Biological Agent Waming Sensor (BAWS)
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From page 74... ...
The log-scale plotting of fluorescence against shape analysis provides a scatter plot that can distinguish biological agents from a variety of molecules that commonly interfere in the analysis. One approach for determining whether biological organisms are living or dead is based on detection of the presence of adenosine triphosphate (ATP)
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From page 75... ...
Accurate detection will require protocols for minimizing extraneous aerosols. STANDOFF DETECTION TECHNOLOGIES Standoff detection technology relies on the measurement of energy transmission through the atmosphere to detect and distinguish biological agents from other atmospheric pollutants.9 The atmosphere has two main components: the molecular atmosphere (primarily oxygen and nitrogen)
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From page 76... ...
Scattering fnam molecules in the air is known as Rayleigh scattering, while scattering from aerosol particulates is Mie scattering.'9 Scattering is a function of the ratio of the molecular or particle diameter to the wavelength of incident light; all aerosol particles will scatter light, but absorption can occur only at specific wavelengths at which electronic transitions can occur in the absorbing species.'9 Standoff detection systems use lasers to illuminate the biological agent aerosol cloud. The incident laser pulse will undergo elastic Mie scattering, with some of the energy being back-scattered to the laser receiver, giving rise to so called elastic backscatter lidar.
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From page 77... ...
, with reported ranges up to 10 kilometers.25 UV-LIF may not specifically distinguish biological agents from other biological material; a fluorescence response at 350 nm after excitation at 260-280 nm only means that protein with tryptophan is probably present. It is not an indication of living organisms, nor is it necessarily distinctive of bacteria.
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From page 78... ...
as the detection limit.33 Projected ranges for a comparable system operating at excitation wavelengths of 355 nm are 2 to 4 kilometers, with sensitivity limits of hundreds of particles per liter of air.34 While UV-LIF systems do allow the discrimination of biological from nonbiological aerosols, they have several shortcomings. They have a shorter range than infrared-based systems, because the shorter ultraviolet wavelengths are more attenuated by the atmosphere.35 They are nonspecific in that they using uv excitation fluorescence: Outdoor test results Field Analytical Chemistry and Technology 15:205-212.
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From page 79... ...
Ultraviolet Resonance Raman Spectroscopy In this technique, ultraviolet light is used to enhance Raman special lines at wavelengths corresponding to elec.Tonic vibrational mode transitions of the target molecule.39 in the laboratory, this ultraviolet resonance Raman (UVRR) technique uses ultraviolet energy to excite DNA49 or protein amino acids4' to excited state saturation, then measures the Raman spectTal shift.
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From page 80... ...
257 nm results in very little fluorescence interference, but these shorter wavelengths propagate even less than the 260 to 280 nm wavelengths discussed above 4~ Preliminary results47 suggest that it may be possible to distinguish different bacterial genera by the differences in intensity of Raman emissions at a specific spectral peak position. Using 228.9 nm as the excitation wavelength results in identical Raman peaks for all genera observed (E.
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From page 81... ...
TERAHERTZ SPECTROSCOPY There is little infommation available concerning terahertz technologies for biological agent aerosol detection. Reportedly, the apeciTa obtained are high in information content but very diff cult to interpret because of the low absorption cross sections.5' While point detection systems for particles are commercially available and relatively inexpensive, the point detection systems that can discriminate biological particles require significantly more sophisticated hardware and manufacturing.
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From page 82... ...
Finding 5~4: There is no currently fielded standoff capability to identify threat biological agents once a biological aerosol has been detected. This is a highly desirable capability that would reduce false ala rims from the large amounts of biological material nommally present in the atmosphere.
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From page 83... ...
POINT AND STANDOFF DETECTION TECHNOLOGIES Finding 5-5: There are technologies and systems currently in use by meteorologists and atmospheric scientists that are similar to those developed by the Department of Defense. Recommendation 5-5: Close monitoring and evaluation should continue of instrumentation, technologies, and techniques (especially those in ultraviolet systems)
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