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Testing and Evaluation of Standoff Chemical Agent Detectors (2003) / Chapter Skim
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4 Recommended Test Protocol and Decision Tree for Active Detectors (Lidar)
Pages 19-23

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From page 19...
... field testing of chemical warfare agents (CWAs) can be avoided if adequate testing of simulants is performed in conjunction with a validated measurement uncertainty model that can realistically and reliably predict lidar performance for CWA measurements in battlefield or home defense environments; 2.
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From page 20...
... These factors entail battlefield environmental factors, including atmospheric scattering and attenuation from various sources; reflected and emitted background radiation sources; vapor, aerosol, and droplet characteristics of CWA releases and their spatial and temporal variation; spectral and spatial characteristics of topographic scattering; and lidar system characteristics as they pertain to measurement performance, such as transmitted energy per pulse, number of pulses averaged per measurement, wavelength stability of the laser source, range to measurement, size of receiver, field of view (FOV) , collection and transmission efficiency (including optical filters)
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From page 21...
... ; · amount and wavelength dependence of background radiation from all sources within expected lidar FOV under conditions that the system will be used; · relevant ambient environmental factors that would affect measurements such as atmospheric temperature, density, and wind; · spatial distribution and physical and optical characteristics of all the different aerosols along the measurement FOV; · spectral absorption characteristics of CWA, concomitant, simulant, and interferent vapors at the relevant spectral resolution for the lidar measurement; · size distribution and refractive index of CWA, concomitant, simulant, and interferent aerosols and droplets; · lidar system parameters that affect measurement of signal-to-noise ratio; · technique-specific operational issues that could contribute to measurement error sources in the model, such as from spectral impurity, laser wavelength jitter, and Doppler broadening of backscattered signal, etc.; and · modeling of the characteristics and uncertainties of the data analysis technique that will be used in the separation of multivariate components to arrive at the concentration of the CWAs such as principal component analyses and neural networks. Note: Some of the atmospheric and topographic scattering and attenuation characteristics will be augmented by lidar measurements made as part of Step 6, and the CWA and simulant parameters will be defined as part of Step 3.
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From page 22...
... Conduct atmospheric tests with simulant and interferent vapors, aerosols, and droplets used in chamber tests to assess lidar system performance at ranges of detection and concentration levels required by the ORD. The range of tests must cover the simulation of all CWA vapors, aerosols, and droplets required by the ORD under a wide range of atmospheric and background conditions with different natural and battlefield aerosol distributions, topographical targets, and CWA release modes, which might affect the encountered aerosol size distributions in different delivery modes.
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From page 23...
... Once the model is determined to accurately predict lidar performance, a series of sensitivity studies can be conducted using measured and assumed parameters for atmospheric conditions, battlefield interferents, backgrounds, topographic scatterers, ranges of measurements, CWA concentrations and delivery methods, etc., to predict the performance of the lidar system in satisfying the ORD. Preliminary studies of this type can be conducted with the model prior to this step; however, it is not until this step that it can be said with confidence that the model is complete enough or accurate enough to predict the lidar system performance for CWA measurements.
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Key Terms

  • measurement uncertainty
  • input parameters
  • lidar measurement
  • sensitivity studies
  • model input

  • atmospheric conditions
  • interferent vapors
  • measurement performance
  • physical characteristics
  • atmospheric tests

  • simulation model
  • measurement simulation
  • assumed parameters
  • lidar performance
  • uncertainty model

  • lidar measurements
  • topographic scatterers
  • model results
  • battlefield environments
  • size distributions

  • cwa concentrations
  • accurately predict
  • delivery methods
  • background conditions
  • spectral dependence

  • topographic scattering
  • reliably predict
  • absorption properties
  • various lidar
  • cwa release


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