Specific detection Flashcards
describe point sensing
this is the processes of taking a sample of an analyte and putting it through s sensing capability
describe standoff sensing
the process of trying to identify a potential threat from a long way away
differences between point and standoff sensing
In point detection applications, the biological organisms must pass through the actual detection element.
Standoff detection is detection of a biological agent cloud at some distance on the order of kilometres from the target and from the detector
What is LIDAR?
LIght, Detection And Ranging
essentially a light illuminated radar system
uses of LIDAR in chem bio sensing
using a UV 297nm laser biological agents can be induced to fluoresce which can then be detected
other uses of LIDAR
navigation and positioning
obstacle detection
plant regrowth
wind speed, turbulence etc (with doppler systems)
speed guns
3d scanning
Define DIAL
Differential absorption lidar
Allows for detection of aerosols and gases in atmosphere
Differences between LIDAR and DIAL
DIAL uses 2 lasers sources, one of the absorption band of interest, the other slightly outside this band and the difference in the intensities allow a concentration of molecule of interest to be calculated
LIDAR is single source and usually based on time of flight
Define LIBS
laser induced breakdown spectroscopy
high power laser beam generates a plasma plume, the cooling plasma allowing elemental emission lines to be observed
Very good for explosive identification
Point detection systems
DNA analysis
PCR
Cas chromatography
Mass Spectrometry
Point sensing cons
ones based on aerosol particle counting with size generate unacceptable false positives
unable to distinguish attack vs normal fluctuations in 1-10um range
Point sensing pros
size and shape analysis combined with UV-LIF is rapid and best used in a building environment due to controllable background noise
oxidation of organisms determined by NAD(P)H fluorescence is a potentially exploitable signature for near real time detection
Standoff detection cons
Long range IR LIDAR cannot distinguish between bio and non bio particles, so high false positive rate
Operational systems need to employ temporal comparisons of spectral signatures to decrease false positive readings due to fluctuations in background signatures.
Standoff pros
Short range use of UV LIF provides near real time discrimination of biological from non biological particles.
The ability to use shorter excitation wavelengths for short distances where atmospheric propagation
is not an issue allows information containing spectral properties to be gathered from aerosolized particles
2 types of LIDAR
direct energy detection (or incoherrent)
coherent detection
