Introducing depolarisation into an inexpensive simple cloud sensor for standoff aerosol detection
2008
Light detection and ranging (LIDAR) has potential to be a successful technique for remote detection of airborne
biological warfare agents (BWA) that pose a health hazard. Potential techniques for detecting BWA often use
spectroscopy to probe molecular structure properties (e.g. UV-fluorescence, Raman and differential absorption
spectroscopy). An alternative approach is to differentiate BWA from background interferents by their differing
morphology; depolarisation offers one such method. Here, we investigate the feasibility of introducing depolarisation
into a short range (approximately 10 m) LIDAR designed to be a simple, inexpensive, low power consumption, portable
instrument.
T-matrix calculations are presented for a randomly oriented, polydisperse size distribution of Bacillus atrophaeus
spheroids. The relationship between backscatter depolarisation and particle aspect ratio is investigated at several incident
wavelengths corresponding to those produced by low cost, commercially available laser sources. Through a series of
simulations, we determine the best combination of wavelengths for a multi-wavelength instrument design that exploits
the concept of normalised depolarisation to determine particle aspect ratio, with the possibility of facilitating BWA
detection.
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