Remote sensing or stand-off detection using controlled light sources is a well known and often used technique for
atmospheric and surface spatial mapping. Today, ground based, vehicle-borne and airborne systems are able to cover
large areas with high accuracy and good reliability. This kind of detection based on LiDAR (Light Detection and
Ranging) or active Differential Optical Absorption Spectroscopy (DOAS) technologies, measures optical responses from
controlled illumination of targets. Properties that can be recorded include volume back-scattering, surface reflectivity,
molecular absorption, induced fluorescence and Raman scattering. The various elastic and inelastic backscattering
responses allow the identification or characterization of content of the target volumes or surfaces. INO has developed
instrumentations to measure distance to solid targets and monitor particles suspended in the air or in water in real time.
Our full waveform LiDAR system is designed for use in numerous applications in environmental or process monitoring
such as dust detection systems, aerosol (pesticide) drift monitoring, liquid level sensing or underwater bathymetric
LiDARs. Our gated imaging developments are used as aids in visibility enhancement or in remote sensing spectroscopy.
Furthermore, when coupled with a spectrograph having a large number of channels, the technique becomes active
multispectral/hyperspectral detection or imaging allowing measurement of ultra-violet laser induced fluorescence (UV
LIF), time resolved fluorescence (in the ns to ms range) as well as gated Raman spectroscopy. These latter techniques
make possible the stand-off detection of bio-aerosols, drugs, explosives as well as the identification of mineral content
for geological survey. This paper reviews the latest technology developments in active remote sensing at INO and
presents on-going projects conducted to address future applications in environmental monitoring.
This paper assesses the potential of detecting explosives (RDX, TNT, PETN, HMX, HMTD, Urea Nitrate) from a
distance with a spectroscopic lidar system. For the study, the temporal and spectral resolutions of laser induced
fluorescence lidar prototypes were enhanced. The integrated breadboards used easily available Nd:YAG laser
wavelengths (266 nm, 355 nm, and 532 nm) to remotely detect the Raman signatures induced in traces of explosives
deposited on surfaces. The spectroscopic lidar setup allows for time resolved measurements with high temporal
resolution. Raman spectra are observable, even in the presence of fluorescence. Experiments with low average laser
power (tens of mWs) have shown the unambiguous capability to detect and identify explosives at distances ranging up to
20 m. Thanks to the combination of UV wavelength for higher Raman cross-sections and efficient gated detection the
355 nm prototype yielded the best compromise. Excitation at 266 nm was expected to yield a better Raman response and
was investigated. Less than optimal laser parameters, detection efficiency and strong fluorescence reduced the signal to
noise ratio of the 266 nm signals with respect to those at 355 nm and 532 nm showing the importance of optimizing
system parameters for high sensitivity detection. Besides the description of the prototypes and an early assessment of
their performances, recommendations are also proposed to improve the instrument, leading to an efficient remote sensor
for explosives.
Standoff detection of explosives residues on surfaces at few meters was made using optical technologies based on
Raman scattering, Laser-Induced Breakdown Spectroscopy (LIBS) and passive standoff FTIR radiometry. By
comparison, detection and analysis of nanogram samples of different explosives was made with a microscope
system where Raman scattering from a micron-size single point illuminated crystal of explosive was observed.
Results from standoff detection experiments using a telescope were compared to experiments using a microscope to
find out important parameters leading to the detection. While detection and spectral identification of the micron-size
explosive particles was possible with a microscope, standoff detection of these particles was very challenging due to
undesired light reflected and produced by the background surface or light coming from other contaminants. Results
illustrated the challenging approach of detecting at a standoff distance the presence of low amount of micron or submicron
explosive particles.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.