Passive and active standoff infrared detection of bio-aerosols

Biological compounds are known to have infrared spectra indicative of speci fic functional groups. There is a strong interest in the use of passive mea ns to detect airborne biological particles, such as spores and cells, which may act as biological weapons. At the sizes of interest, the infrared spec tra of bacterial particles result from a combination of geometric (pi d(par ticle) > lambda) and Mie (pi d(particle) similar to lambda) scattering proc esses, whereas the infrared spectrum of atmospheric particles falls into th e Rayleigh limit (pi d(particle) much less than lambda). In this article we report on laboratory measurements of the infrared spectra of aerosolized B acillus subtilis (BG) spores in air under controlled measurement conditions . Transmission measurements show an in spectrum of the spores with features comparable to the condensed phase spectrum superimposed on a background of Mie scattering. Preliminary measurements indicate a peak extinction coeffi cient of approximately 1.6 x 10(-8) cm(2) per spore at 9.65 mu m. These res ults are discussed in terms of their implication for passive and active inf rared detection and identification of bio-aerosols, (C) 1999 John Wiley & S ons, Inc.