Airglow studies using observations made with the

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Airglow studies using observations made with the
GLO instrument on the space shuttle

• Introduction
• GLO instrument
• Tomography - Least-squares method
• Calculation of the path lengths
• Conclusion

• INTRODUCTION
• Airglow emission layers exhibit spatial and
  temporal fluctuations attributed to the passage
  of atmospheric gravity waves through these
  layers.
• They induce density and temperature
  perturbations
• Observations of nightglow structures give
  excellent information on atmospheric gravity waves

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REC 2001

• TOMOGRAPHY
• Remote sensing tool
• Can be used to estimate the distribution of
  volume emission rate
• It can reveal structures that are undetectable in
  single images

• The GLO instrument
• Hyperspectral imager
• Flew on shuttle missions 53, 63,69,74 and 85
• Mission STS-69
• September 1995, shuttle Endeavor

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Tomographic inversion

• Reconstruction grid
• The airglow emission rates are assumed to be
  uniform within each grid element so that each
  measured brightness may be treated as the sum of
  the contributions from all the elements that lie
  along the line of sight

LEAST-SQUARES METHOD The process is initiated
using a uniform distribution of Vj.
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Least-squares method
At each iteration step a new set of volume
emission rates is obtained from the previous set
using the iteration formula
Which constrains the Vjs to be positive The
quantity ?Vj varies from element to element and
is given by
The iterative process is terminated when the
recovered volume emission rates have converged on
a stable solution.
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The reconstruction grid
The region of the atmosphere, lying between
altitudes of 51 and 116 km and extending along a
95 degree segment of the shuttle orbit plane, has
been divided into 1120 cells each 1.35 degrees
wide and 4km high. We have a set of 74 images and
a total of 1480 observations.
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Final remarks and conclusion

• The emission of the O2(0-0) atmospheric band has
  been chosen to be analyzed first since it is a
  bright emission in the nightglow spectrum
• Synthetic data with no absorption will be used to
  test the tomographic inversion program
• The process will be repeated using actual GLO
  observations
• It will be necessary to calculate line by line
  the absorption correction coefficients.
  Degenstein has shown absorption can be
  represented by a factor multiplying the path
  lengths and that the calculation of this factor
  does not require an exact knowledge of the
  atmosphere and any appropriate model is adequate
  for analysis.