Image Coalignment of SolarB SOTXRTEIS Data

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Image Co-alignment of Solar-B SOT/XRT/EIS Data
T. Shimizu (ISAS/JAXA)
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Introduction
Solar-B

• Position information is included in Solar-B
  image header
• In order to indicate where on the disk is
  observed.
• Mainly used for database search and operation
  planning
• Accuracy may not be adequate for data analysis.
  A few tens arcsec deviation at worst case.
• Image co-alignment needs to be performed in data
  analysis
• To co-align among data from Solar-B telescopes
• Relative relation among the telescope pointings
• 0.5 arcsec or better accuracy required
• To co-align Solar-B data with data from other
  observations
• Other observations satellites,
  ground-based
• Absolute coordinate on the solar disk
• 1 arcsec accuracy required

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• Telescopes are mounted on stable cylindrical
  optical bench (OBU)
• However, each telescope pointing has different
  orbital variation due to thermal deformation
  including barbecue effect

OBU
2D trajectory map of orbital variation of
pointings) (Prediction based on thermal
deformation test, Hot case)
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Baseline between-telescopes alignment procedure
Common solar features are used to co-align the
data from different telescopes with each other.
Common features are sunspots seen both in SOT
continuum/G-band image and XRT VLS images.
Accuracy is in order of 0.1 arcsec.
Images of interest
Need a visible image in XRT sequence within 10
minutes
There is a time gap between sunspot image and
images of interest. The time series of each
telescopes images are co-aligned by the
procedure shown later.
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Between-telescopes alignment procedure (1)
Co-Alignment between XRT and SOT
Solar-B
Zoom up
time
Images of interest for comparison
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Between-telescopes alignment procedure (2)
Co-aligning series of SOT images
Solar-B
SOT (Filtergram, Spectro-Polarimeter) Data
time

• Satellite jitter is already removed in series of
  SOT images
• Tip-tilt mirror with correlation tracker removes
  satellite jitter
• Tip-tilt mirror control tracks the group motion
  of granules seen in the correlation-trackers
  field of view (11x11arcsec).
• If 0.5km/s group flow exists in CT FOV,
• 600 sec (10 min) period produces 0.4 arcsec
  alignment shift.

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Between-telescopes alignment procedure (3)
Co-aligning series of XRT images
Solar-B
XRT and EIS Data
time
S/C jitter

• Satellite jitter is included in series of XRT
  images.
• Sun sensor (UFSS)s information can be used to
  remove satellite jitter. Sensors random error is
  0.3 arcsec (0-p).

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Between-telescopes alignment procedureXRT VLS
micro-vibration concern
Solar-B

• There is a concern on slight degradation of SOT
  image performance when XRT VLS (visible light
  shutter) is rotating (lt a few sec).
• VLS produces fairly large micro-vibration
  during its rotation, which may shake SOT optics
  during the rotation.
• (Result from satellite-level
  micro-vibration test)
• 10 minutes cadence of VLS images may not be
  performed. If not, VLS cadence may be once per
  orbit (90 min).
• Alternate co-alignment concept may apply (next
  page).

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Alternate co-alignment concept (by SAO)
SOT
No limb info in data
(x0,y0)
(x1,y1)
(xp,yp) Sunspot position wrt the limb is
interpolated from (x0,y0) and (x1,y1)
Includes drift due to granule motions
Short-term satellite jitter removed with UFSS data
XRT
Visible light
X-ray
Visible light
X-ray
(x0,y0)
(x1,y1)
Sunspot position wrt the limb
(xp,yp) at the corner of FOV is known from the
X-ray limb and UFSS
Alignment using limb for 45min (max)
90min
t090min
t0
t
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Co-Alignment with Non-Solar-B Data
Solar-B

• To co-align Solar-B data with data from other
  observations
• Other observations satellites, ground-based
• Absolute coordinate on the solar disk
• 1 arcsec accuracy required

• The way to have 1 arcsec
• accuracy in absolute coordinate
• is to use limb position in full-
• disk images from XRT.

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