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Testing and Evaluation of Standoff Chemical Agent Detectors (2003) / Chapter Skim
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5 Simulant Characteristics and Specifics
Pages 24-26

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From page 24...
... In this context the next sections discuss spectral simulants; that is, chemicals that have the necessary properties to calibrate the infrared spectral detector, and aerosol simulants; that is, chemicals that mimic the physical dispersion characteristics of CWAs as necessary components of the background and delivery concomitants that the detector might "see." SPECTRAL SIMULANTS The type of compounds suitable as spectral simulants are those that give rise to similar spectral characteristics observed for a given CWA in the 10 Em atmospheric window, that is, between 700 and 1,300 cam. This criterion does not necessarily mean that the chemical structure of the simulant should be similar to that of the CWA; however, in light of the fact that most functional groups give rise to absorption bands that absorb in a characteristic frequency range, this is quite likely.
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From page 25...
... The contribution of aerosol particles to the total extinction coefficient of the atmosphere along the line of sight is, thus, an integral over the product of the size-dependent scattering efficiency and the particle size distribution function. Moreover, even nonabsorbing particles scatter radiant energy, so the background aerosol will contribute to and in many cases dominate this mechanism of degradation of the remote sensing signal.
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From page 26...
... the influence of background aerosols on signals from both vapor and particulate agent. While exact duplication of the conditions of any battlefield release is unlikely, method validation is possible by "closure" studies in which the aerosol properties are characterized by in situ measurements of particle concentrations and size distribution, chemical composition, optical properties, etc., thereby enabling a direct comparison of modeled sensor response with field performance.
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Key Terms

  • size distribution
  • absorption bands
  • spectral simulants
  • absorption efficiency
  • passive infrared

  • particles scatter
  • material properties
  • suspended particles
  • vapor pressure
  • surface tension

  • optical properties
  • scattering efficiency
  • absorbing species
  • particulate agent
  • aerosol particles

  • infrared measurements
  • field performance
  • mie scattering
  • aerosol formation
  • compounds suitable

  • particle diameter
  • chamber experiments
  • detect absorbing
  • direct radiative
  • thereby enabling

  • require matching
  • substantially larger
  • active measurements
  • optical absorption
  • emission properties


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