SolarB Data CoAlignment Plan

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Solar-B Data Co-Alignment Plan
Solar-B MODA Working Group Meeting _at_SAO, 2002.7
Solar-B 4th Science meeting_at_ISAS, 2003.2

• T.Shimizu (NAOJ)
• Shimizu_at_solar.mtk.nao.ac.jp

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Background
Solar-B

• Co-alignment of data from three
• telescopes is one of keys for Solar-B
• sciences
• Sub arcsec accuracy ( SOT resolution)
• is required for Photosphere-Corona
• connectivity detailed studies
• Telescopes are mounted on stable
• cylindrical optical bench (OBU)
• However, the pointing of telescopes
• relative to other telescope is not perfect
• due to thermal deformation
• - Rotating barbecue effect
• (orbital period)
• - Temperature potential change
• (maybe seasonal period)

OBU
XRT integration in MTM test
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Thermal Deformation Test
Solar-B

• Pointing errors due to thermal deformation was
  measured in November.
• BUSOBU with dummy telescopes
• BUS and OBU with asymmetrical temperature
  distribution
• Measured with laser interferometers and
  autocollimator

Laser interferometer system on a dummy
(plate-like) telescope
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Thermal Deformation Test
Solar-B

• Measured pointing errors
• Data analysis is still in progress by MELCO
  system
• Preliminary
• Asymmetry in OBU
• 8 arcsec (max) observed with 10 deg C
  asymmetry
• On-orbit 1.5 deg C asymmetry ? 1.2
  arcsec (max)
• Asymmetry in BUS
• 2-3 arcsec (max) observed with 10 deg C
  asymmetry

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Attitude Sensors
Solar-B
Sun-sensors

• Attitude sensors can provide the
• data necessary for data co-alignment
• Attitude sensors are installed in
• IRU box tower attached to OBU
• Gyros (IRU-SA) ? in BUS
• The pointing of sun-sensors relative
• to telescope is not perfect due to
• thermal deformation

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Purposes and Required Accuracy
Solar-B

• For what purposes, do we need pointing
  information?
• To know where are observed with Solar-B
  telescopes
• (Useful for operation planning and database
  search)
• Absolute coordinate on the solar disk
• 20 arcsec accuracy enough
• 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 needed
• To co-align among data from Solar-B telescopes
• Relative relation among the telescope pointings
• Sub-arcsec accuracy ( SOT resolution) needed

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Solar-B Pointing Information
Solar-B

• UFSS (Ultra Fine Sun Sensor)
• Main sensor redundancy sensor
• Position of sun center in 2 axis (X, Y) (arcsec)
• High resolution
• IRU (Inertia Reference Unit Gyro-scope)
• Main sensor redundancy sensor
• Angular velocity in X, Y Z (arcsec/sec)
• Highest resolution, but not angle
• STT (Star Tracker)
• Position of Canopus (a Cen) to control around
  Z axis
• Can be used for correcting image rotation.
• Others
• NSAS (Non-Spin-type sun aspect sensor)
• GAS (Geomagnetic sensor)

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Where observed?
Solar-B

• To know where are observed with Solar-B
  telescopes
• (Useful for operation planning and database
  search)
• Absolute coordinate on the solar disk
• 20 arcsec accuracy enough

System requirement Absolute Pointing accuracy
(over mission life) 20 arcsec 0-p
(X, Y) 145 arcsec 0-p (Z)
(from SOT)

• Without any correction by using attitude data,
  enough accuracy will be expected for this
  purpose.
• To include this information in FITS header
• But notice that its accuracy is poor for
  scientific
• data analysis

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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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Co-Alignment with Non-Solar-B Data
Solar-B

• Cross-correlation between XRT full-disk images
  and attitude
• pointing data will calibrate the attitude data
• Accumulating the cross-correlation allows us to
  make a model
• for the calibration. Longer accumulation will
  improve the model.

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Co-Alignment of Solar-B Data
Solar-B

• To co-align among data from Solar-B telescopes
• Relative relation among the telescope points
• Sub-arcsec accuracy ( SOT resolution) required

Example
time
How can we have high accuracy in relative
coordinate?
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Co-Alignment of Solar-B Data
Solar-B

• The images with same solar features are used to
  co-align the data from different telescopes with
  each other.
• Sunspots seen in SOT continuum and XRT aspect
  images
• QS Network features seen in SOT magnetogram and
  EIS images

time
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Co-Alignment of Solar-B Data
Solar-B
XRT and EIS Data
time
S/C jitter

• To well co-align images along in time, we need to
  consider ...
• Satellite jitter is included in image sequences.
• Attitude (UFSS, IRU) data can be used to remove
  satellite jitter.
• Internal mis-alignment, e.g.,
• XRT X-ray optical axis and WL aspect sensor
  axis
• EIS error in scanning mirror positioning

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Co-Alignment of Solar-B Data
Solar-B
SOT (Filtergram, Spectro-Polarimeter) Data
time

• To well co-align images along in time, we need to
  consider ...
• Satellite jitter is already removed in sequence
  of SOT images
• Tip-tilt mirror with correlation tracker removes
  satellite jitter
• Internal mis-alignment, e.g.,
• Filtergram image shift caused by Filter wedge
• Spectro-polarimeter error in scanning mirror
  positioning

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Database for Co-Alignment
Solar-B

• Requirements for attitude database
• The database should be convenient for modeling
  the calibration (temporal evolution) for attitude
  data
• Time sequence of attitude data
• To use IRU (output angular velocity) data
• Separated from the image database
• Need time stamp to identify attitude data at the
  time when
• an image is exposed
• Need other information
• Orbital phase information
• Thermal condition (measured temperatures)

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Database for Co-Alignment
Solar-B

• Pointing information in image database
• Target information in absolute coordinate is
  useful
• Need a note about accuracy in analysis guide
• Accuracy in order of less than 10-20 arcsec in
  absolute
• coordinate will need a calibration
• The calibration is cross-correlation between XRT
  full-
• disk images and attitude pointing data
• Accumulating the cross-correlation allows us to
  make a model
• for the calibration. Longer
  accumulation will improve the model
• Two ways to obtain more accurate address
• Update the image header when the calibration is
  improved
• (Not recommended)
• Provide a S/W to calculate (I like)
• If the calculation should be performed only
  with image data,
• the image header should contain attitude
  data, orbital phase,
• thermal condition