Airglow studies using observations made with the GLO Instrument on the Space Shuttle

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Airglow studies using observations made with the
GLO Instrument on the Space Shuttle

• REC 2001
• Ana Luisa Alfaro Suzán

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Outline

• Introduction
• The GLO Instrument
• Tomography
• Limb viewing geometry
• Tomographic inversion algorithms
• Future work

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Introduction

• Observations of airglow emission rates provide a
  powerful mean of remotely sensing the state of
  the upper atmosphere.
• Processes
• Excitation of atoms and molecules
• Recombination of atoms to form molecules
• Recombination of ions and electrons to form
  neutral atoms or molecules.

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The GLO Instrument

• The GLO Instrument comprises a nine-section
  spectrograph, monochromatic imagers, wide
  bandwidth CCD imagers, and a TV camera - all line
  of sighted to view in the same direction.
• The spectrographs simultaneously observe the
  entire wavelength range from 1150Å to 9000Å

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Image of the Earth airglow layer
This image was taken by the GLO support imager.
There are five stars visible in the field. One
program predicts the RA and Dec of a star
appearing in the imager FOV. A 2nd program
calculates the AZ/EL position of the star in an
ideal GLO coordinate system.
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Segment of a GLO spectral image
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Mission STS-69

• The GLO instrument flew on the Shuttle Endeavor
  in September 1995.

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Tomography

• Tomography is used to determine the internal
  structure of an object.
• Tomographic inversion can be used to estimate the
  distribution of volume emission rates.
• The gross features of the spatial variations can
  be obtained from a series of sequential
  non-tomographic 1-dimensional inversions of the
  limb profiles. However this approach can lead to
  erroneous results. (McDade and Llewellyn, 1993)

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Limb viewing
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Reconstruction Grid

• The region of the atmosphere lying between
  altitudes of 52 and 116 km and extending along a
  95 segment of the shuttle orbit plane, has been
  divided into 1120 rectangular cells each 1.3
  wide and 4 km high.

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The measured airglow limb brightness, Oi, can be
expressed in terms of the volume emission rates
within the grid elements weighted by the
geometric path length, Lij, through each
element. Jtot is the total number of elements for
which the volume emission rates are to be
recovered j1,.., Jtot Nobs is the total of
independent line of sight measurements i1,..,
Nobs
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Tomographic inversion algorithms

• The maximum probability algorithm finds the set
  of volume emission rates that has the highest
  probability of having produced the entire set of
  observations
• The least-squares algorithm seeks the set of
  volume emission rates that minimizes an error
  function

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The strongest features of the terrestrial night
time airglow
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Future research

• Data quality surveys will be performed and
  suitable orbits will be selected for analysis.
• The emission of the O2(0-0) atmospheric band will
  be studied first since it is the brightest
  emission in the nightglow spectrum observed from
  orbit.
• Tomographic inversion routines will be modified
  for use with GLO data. In the first phase
  synthetic data at GLO quality with no absorption
  will be used. This will be repeated with
  absorption using existing O2(0-0) absorption
  code. Finally, the inversion routines will be
  applied to actual GLO observations.

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• Picture taken during the STS-39 mission in
  April/May 1991