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The Concentration Probability Density Function With Implications for Probabilistic Modeling of Chemical Warfare Agent Detector Responses for Source Reconstruction

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Technical rept.

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The relationships between various normalized higher-order concentration moments have been investigated using a large data set of concentration fluctuations obtained in a boundary-layer water channel with high-resolution laser-induced fluorescence. This data set corresponds to a series of comprehensive measurements of plume dispersion in a number of obstacle arrays e.g., various arrays of cubical and non-cubical obstacles in aligned and staggered arrangements with uniform and random heights. A remarkably robust feature of all the concentration data was the observed collapse, of the third- and fourth-order normalized concentration moments on the second-order normalized concentration moment and of the concentration kurtosis on the concentration skewness, to a series of universal curves. These universal curves were identical to those observed previously for open-terrain plumes, and are well modeled using either a clippedgamma probability density function PDF or the simpler intermittent exponential PDF for the concentration. A comparison of the shape of the model probability distributions to the measured concentration data at various plume locations showed that the clipped-gamma distribution provided a good representation for the general distribution shape, whereas the simpler intermittent exponential distribution yielded a poor conformance to the measured concentration probability distribution in spite of the fact that both of the model distributions gave a good representation for the first four concentration moments. The implication of the form of the concentration PDF, for the formulation of a probabilistic model for the response of a chemical agent detector, is investigated in the context of the source reconstruction problem. 14.

Subject Categories:

  • Physical Chemistry
  • Statistics and Probability
  • Chemical, Biological and Radiological Warfare
  • Miscellaneous Detection and Detectors

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