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Solar-B Data Co-Alignment Plan

Solar-B MO&DA Working Group Meeting @SAO, 2002.7. Solar-B Data Co-Alignment Plan. Solar-B 4 th Science meeting@ISAS, 2003.2. T.Shimizu (NAOJ) Shimizu@solar.mtk.nao.ac.jp. Background. Solar-B. Co-alignment of data from three telescopes is one of keys for Solar-B sciences

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Solar-B Data Co-Alignment Plan

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  1. Solar-B MO&DA Working Group Meeting @SAO, 2002.7 Solar-B Data Co-Alignment Plan Solar-B 4th Science meeting@ISAS, 2003.2 T.Shimizu (NAOJ) Shimizu@solar.mtk.nao.ac.jp

  2. 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

  3. Thermal Deformation Test Dummy telescopes OBU Solar-B • Pointing errors due to thermal deformation was measured in November. • BUS+OBU 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

  4. 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

  5. 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

  6. 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

  7. 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)

  8. 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

  9. 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.

  10. 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.

  11. 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?

  12. 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

  13. 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

  14. 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

  15. 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)

  16. 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

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