HIRDLS Update

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HIRDLS Update
John Gille John Barnett Univ. of
Colorado/NCAR Oxford University

• Aura Science Team
• Pasadena CA
• 2 March 2005

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Map of channel 1 radiance counts across the
viewing aperture based on first scans made
immediately after cooling the detectors in August
2004.
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HIRDLS Proto Flight Model
Towards the Earth
fixed sun shield
velocity vector
moving sun shield door
viewing aperture
coolers
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Door tests used to map blockage in
December/January.

• Door closed in 1.5 deg steps each orbit gave 2
  new results
• Above 95 deg door angle the sun warmed the
  blockage at sunset, which showed in the radiance
  channels below 95 deg did not gave a fix on
  location of end of blockage.
• Below 18 deg door began to intrude into beam
  viewing at -48 deg gave second fix on end of
  blockage test repeated with smaller steps.

View of the aperture plane from outside the
instrument showing end-of-door sun shadow lines
for door angles 121.5 to 81.6 deg for first door
test.
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Based on tests performed by LMMS blockage was
believed to be a piece of Kapton which was
supposed to be behind the scan mirror but during
ascent has ballooned out, been torn, and had
moved in front of the scanner. Geometry fitted
with a nearly flat surface (series of triangles)
based on door tests. Cyan curves show -48 deg
beams for two channels where the intersect fitted
blockage (black triangles). View is along the -48
deg beam.
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As before (beam edges in cyan just visible)
plus rays (magenta) modelled by Swales for the
same beam direction , but fitting an optical
model to radiances. i.e. totally independent
type of fit (no relation to door test
information).
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Profile Locations Yesterday
Atmospheric profile locations for 24 hours up to
2236 hours 1 March
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Plan to Correct Radiometric Signals
Edge ofObscuration
Aperture
Space

Sun
BeamFootprint
Obscuration
Earth

• Obscuration covers most of aperture
• Beam has partial view to atmosphere at azimuth
  furthest from sun
• To use, the following steps are necessary
• Radiometric calibration
• Removal of blockage contribution from signal
• Correction for reduced area
• Filtering of over-sampled data

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Approach to Correcting for Blockage Signal
Underlying Assumptions Effect of blockage
at azimuth angles 23.5, -22.4 where vertical
science scans made is product of constant
geometric effect of blockage plus optical beam,
and blackbody radiance from it. Blockage
radiance can be measured by scanning over it.
Temperature distribution of blockage and
radiation from it are essentially the same when
in normal orientation, and when HIRDLS Field of
Regard pitched up by 5.25. Measurements
during pitch-up maneuver can be used to determine
geometric relationships between radiance from
blockage and its component at science scan
azimuth angle, Rs. Then, if we measure R during
a science scan, atmospheric radiance from
reduced aperture given by R-Rs. To convert to
radiance from full aperture, R, divide by
fractional area of aperture A, so R (R -
Rs)/ A. Final step - filter to reduce to
signal bandwidth, and reduce noise.
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Example of Radiance Correction- Channel 2
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Retrieved HIRDLS Temperatures 21 January 2005,
2200-2400
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Curtain Plot Comparisons
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Profile Resolution Unaffected

• The resolution is determined in large part by
  noise.
• Width of averaging kernels not appreciably
  affected by increased noise in this range
• Example of ozone retrievals (right) shows
  capability to recover high resolution in
  UpperTroposphere/
• Lower Stratosphere (UTLS) region, see thin
  layer.
• Data will be retrieved with 1 km vertical
  resolution.

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Conclusions from Plausibility Demonstration and
Comparisons to Baseline

• Plausibility demo shows
• Blockage removal and aperture area correction can
  be done, gets radiances and retrievals in right
  ballpark
• Works in all parts of orbit
• Retains high resolution information
• Signals are largest, results will be best in
  UT/LS altitudes
• Altitude Range of retrievals very similar to
  baseline
• Vertical Resolution very similar to baseline

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Fit of Radiances at Azimuth Angle -23.5 as a
Function of Radiances at -18
Data from the Pitch Maneuver on 9 February have
been used to develop parameterizations of Rs as
function of radiance at -18
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Present HIRDLS Science Scan Pattern
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Revised Scan Pattern and Coverage

• The revised scan pattern has been used since
  before PAVE validation flights. It scans
  atmosphere at left-most azimuth, also blockage to
  determine corrections.

HIRDLS Coverage, and comparison to MLS
HIRDLS Coverage 65S to 80 N, (94.6 of globe)
longitudinal resolution 24.75 (like MLS TES)
Along track- 3 profiles/280 km 6950/day (89 of
base 7850) Close overlap with MLS at night
(descending), between orbits in daytime. Time
difference 99 minutes 15 minutes- usually
close enough for valid comparisons
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Summary

• Blockage found in optical train. 8 Complex tests
  to move blockage unsuccessful. High horizontal
  resolution precluded.
• Otherwise, HIRDLS functioning as very accurate,
  precise and stable radiometer
• One beam width, at extreme anti-sun side of
  aperture, 20 clear
• Because of large beam (140 mm diameter),
  remaining area equivalent to 63 mm beam diameter
• Very low noise detectors allow recovery of large
  part of science data from reduced beam
• Data correction complex, need 8 months (to Sept.
  05) to implement, test and verify
• HIRDLS retains most scientific capabilities to
  support Aura Mission