KEYWORDS: LIDAR, Aerosols, Analog electronics, Signal to noise ratio, Sensors, Clouds, Telescopes, Atmospheric particles, Signal detection, Laser energy
Remote detection of biological warfare agents (BWA) is crucial for providing early warning to ensure maximum survivability of personnel in the battlefield and other sensitive areas. Although the current generation of stand- off aerosol and fluorescence lidars have demonstrated stand- off detection and identification of BWA, their large size and cost make them difficult for field use. We have introduced a new eye-safe portable digital lidar (PDL) technique based on digital detection that achieves orders of magnitude reduction in the size, cost and complexity over the conventional lidar, while providing an equal or better sensitivity and range. Excellent performance has been obtained with two of our PDL sensors during two bio-aerosol measurement campaigns carried out at Dugway Proving Grounds. In the JFT 4.5 (Oct 98) tests, high aerosol sensitivity of 300 ppl of biosimulant particles at up to 3 km was demonstrated with an eye-safe wavelength (523nm) aerosol micro PDL that utilized a 8 inch telescope, <10(mu) J/pulse energy at 2.5kHz, photon counting digital detection and 2 sec averaging. For the JBREWS DFT (June 99) tests an eye-safe two wavelengths (523nm and 1.047mum) horizontally scanned, aerosol micro PDL with the same 8 inch telescope was utilized. With this lidar, high sensitivity, preliminary differentiation between natural and unusual clouds, and the ability to track the aerosol cloud location, their wind speed and direction were also demonstrated. Lidar simulations of both PDL and conventional analog detection have been performed. Based on these model calculations and experimental results an analysis and comparison of the inherent capabilities of two types of systems is given.
Photoelasticity has been used recently by the authors to conduct many tests related to the determination of stresses in the field of tall beams and to the optimization of those beams. Numerical methods (in particular, finite elements and solutions of Laplace's equation) have also been used to supplement or verify the results obtained photoelastically. This paper deals with selected aspects of some of the results obtained and evaluates the advantages and disadvantages of the methods used in the solution of
the particular problems addressed.
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