Scene Change Artifacts in Fourier Transform Spectroscopy of Temporally Changing Sources

Abstract

Improved understanding of midwave infrared (1-5 micron) spectral emissions from detonation fireballs is needed to develop phenomenological models for battle space optical forensics. The ability to measure radiance over a wide band pass at arbitrary resolutions make Fourier-transform spectrometers (FTS) an attractive tool. However, interferometer based spectroscopic measurements can be corrupted when the observed intensity changes during data acquisition. While small, random fluctuations in scene intensity translate into noise, systematic variations introduce scene-change artifacts (SCAs)into Fourier-transformed spectrum. Approximating a detonation fireball as a blackbody radiator, modified with an atmospheric attenuation Tatm,with an exponentially cooling temperature T(t)=T0e^-kt,double sided interferograms from an ideal Michelson interferometer were simulated and converted to a measured spectrum Lm to characterize the nature and magnitude of SCAs. With T0=1500K, changing scene spectra on 0<&#61485;v<7900cm^-1 at o&#61485;v=0.04cm^-1 resolution were computed with percent changes in T (t ) between 0 and 80%. The real part of Lm(Re{Lm})is well approximated by the instantaneous spectrum(Lzpd)at zero path difference. Differences between Re{Lm}and Lzpd (Re{lm}-Lzpd)is largest when Tatm is highly structured and these differences increase with the amount of temperature change during the measurement. Similarly, the imaginary part of Lm(Im{Lm})exhibits highly structured features whenever Tatm changes rapidly with V. In general, Im{Lm}>Re{Lm}-Lzpd agreeing with previous theoretical work and the increase in magnitude of Im{Lm}with temperature change is more pronounced than Re{Lm}-Lzpd.These trends were independent of initial temperature, spectral resolution, or choice of Tatm. For a MOPD = .5cm, a 4% reduction in temperature during a single scan produced an RMS value of Lzpd was

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Document Details

Document Type
Technical Report
Publication Date
Mar 01, 2010
Accession Number
ADA516513

Entities

People

  • Anthony M. Young

Organizations

  • Air Force Institute of Technology

Tags

Communities of Interest

  • Counter IED
  • Energy and Power Technologies
  • Weapons Technologies

DTIC Thesaurus Topics

  • Acquisition
  • Air Force
  • Climate Change
  • Data Acquisition
  • Detectors
  • Detonations
  • Frequency
  • Incandescent Lamps
  • Intensity
  • Interferograms
  • Interferometers
  • Lamps
  • Measurement
  • Michelson Interferometers
  • Spectra
  • Spectral Lines
  • Spectroscopy

Fields of Study

  • Physics

Readers

  • Approximation Theory.
  • Computer Vision.
  • Spectroscopy.

Technology Areas

  • Space