1 Solar-B Data Co-Alignment Plan T.Shimizu (NAOJ) [email protected] Solar-B MO&DA Working Group Meeting @SAO, 2002.7 Solar-B 4 th Science meeting@ISAS,

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Solar-B Data Co-Alignment Plan

T.Shimizu (NAOJ)[email protected]

Solar-B MO&DA Working Group Meeting @SAO, 2002.7

Solar-B 4th Science meeting@ISAS, 2003.2

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Solar-B Background

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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Solar-B Thermal Deformation Test

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

Dummy telescopes

OBU

Laser interferometer system on a dummy (plate-like) telescope

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Solar-B Thermal Deformation Test

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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Solar-B Attitude 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

Sun-sensors

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Solar-B Purposes and Required Accuracy

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 observationsOther 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 Solar-B Pointing Information

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” ( 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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Solar-B Where observed?

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

To co-align Solar-B data with data from other observationsOther 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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Solar-B Co-Alignment with Non-Solar-B Data

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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Solar-B Co-Alignment of Solar-B Data

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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Solar-B Co-Alignment of Solar-B Data

time

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

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Solar-B Co-Alignment of Solar-B Data

time

XRT and EIS Data

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

S/C jitter

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Solar-B Co-Alignment of Solar-B Data

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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Solar-B Database for Co-Alignment

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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Solar-B Database for Co-Alignment

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