The Solar Optical
Telescope and its
Focal Plane Package

The primary goal of the Solar-B mission
is to advance our understanding of theorigin of the outer solar atmosphere,
the corona, and of the coupling
between the fine magnetic structure atthe photosphere and the dynamic
processes occurring in the corona.

Primary Science Tasks
Detailed studies of vector magnetic field structure, evolution anddiscontinuous changes on all spatial scales ranging from micro-flaresto the very largest explosive events to determine whether these eventsare different manifestations of the same or similar process.
A determination of whether the quasi-steady state magnetic field plays
an active or passive role in coronal heating.
A determination of whether the solar cycle spectral irradiance variation
has a magnetic origin and the nature of the controlling mechanism
identified.
From the knowledge of the three-dimensional structure of the coronalfield, studies of how the field is restructured in transient events will
be performed to provide unambiguous evidence for magnetic
reconnection.
The dependence of network and intra-network magnetic structure andactivity on latitude and proximity of sunspot groups will be
determined.

Features of the Solar Optical
Telescope System
Diffraction-limited images (0.2-0.3 arcsec), achieved by a
50 cm-diameter aperture Gregorian Telescope388-668 nm spectral range that contains spectral lines andcontinuum bands useful for studying photosphere andchromosphere
Telescope optimized for minimum polarization to allow
accurate measurement of vector magnetic fields
Observation from space, free from the atmospheric seeing
Active tip-tilt mirror to remove spacecraft jitter
Continuous observation for during ~8 months per year, due
to the sun-synchronous polar orbit

Optical Telescope Assembly (OTA)
Secondary mirror

Side door

Heat dump mirror
Top door

CFRP truss structurePrimary mirror
Collimator lensPolarization modulator
Tip-tilt mirror

OTA Components

Collimator Lens
Secondary Mirror

PMU

Primary Mirror
CFRP Truss Structure

Tip-Tilt Mirror

Solar B Assembly in Test

OTA

FPP
OBU

SOT System Block Diagram
Heat Dump Beam

CTM-TE

CTM-E

Tip-tilt mirror(CTM-TM)

Solar Beam

Observation sequence
MDP
control

Telescope (OTA)

Image datacompression

FPP-E

Polarization modulator (PMU)

Focal Plane Package (FPP)
Science Instruments

SpacecraftFPP Science Systems
The SOT broadband filter imager (BFI) records diffraction-limited
images, over the wavelength range 396.8 nm to 668.4 nm toobserve both photospheric and chromospheric structure in quiet
and active Sun. lrradiance data is obtained from observations in
the blue (450.45 nm), green (596.25 nm) and red (668.40 nm)
continuum.
The SOT narrowband filter imager (NFI) records high spatial
resolution (250 km) rapid for large (160 x 160 arcsecond) field ofviews, moderate polarimetric accuracy (10-2 or better)magnetograms over the full range of magnetic conditions fromquiet Sun to moderate scale active regions.
The SOT Spectro-Polarimeter (SP) records the photospheric vector
magnetic fields of both quiet and active Sun with the highest
possible precision (polarimetric accuracy 10-3 or better), observing
the vector magnetic field over spatial scales of 500 km.
9FPP Optics Package
Spectro-Polarimeter:
High resolutions Stokes Parameters (~.0025 nm)
Scans to generate images
Evolution of HAO - Advanced Stokes Polarimeter

Broad Band Filter System
2-D Images at High Temporal & Spatial Resolution
Six Spectral Bands (~.8 nm)
Correlation Tracker
Removes spacecraft
jitterTunable Filter System
2-D Images in a single wavelength (~.01 nm)
Tunes (~.0005 nm) to form velocity and magnetic maps

View Toward to Grating
SP
NFI
BFI

CT

Light From Telescope

Spectro-Polarimeter (SP)
2 spectra are taken simultaneously in
2 orthogonal polarizations
High accuracy: s/n~1000 in a normal map
320 arcsec

The slit can scan to map a finite area. A normal
wide scan is 320 “ (2000 steps). Smaller scans canbe used to achieve high time resoluton.

Spectro-Polarimeter Observables
Spectra of two Fe lines at 630.15 and 630.25 nm and nearby
continuum are exposed, with a 0.16 x 164 arcsecond slit
2 spectra taken simultaneously in orthogonal linear polarizations
Spectra are exposed and read out continuously, 16 times per rotation of the
Polarization Modulator

Raw spectra are added & subtracted into 4 memories to“demodulate,” forming Stokes Parameters I, Q, U, V
Single observation is 2 sets of IQUV spectra (from the 2 linear pols.)

The slit may be moved between observations to map a finite area
A wide single scan maps an entire active region
Repeated narrow scans study small features with high time resolution

Processing on the ground produces maps of magnetic field vectors,
Doppler shifts, and thermal properties on the Sun

Dual Spectra in SP Focal Plane

This image from the SP focal plane was made in test of
the FPP using a light feed from the laboratory heliostat.

SP Observing Modes -1
Normal Observing Mode
Expose/Read/Demodulate for 3 full rotations of waveplate, polarimetricaccuracy of 0.001
Raw data is 120 x 2 spectral pixels x 1024 spatial pixels x 4 Stokes parametersin 4.8 sec, which is 983 Kpixels or 205 Kpixels/sec
Send to MDP for optional compression and downlink
Maps area 1.6” wide in 50” or 160” wide in 83 min.

Fast Map Mode
Expose/Read/Demodulate for 1 full rotation of waveplate, step the slit 0.16”,
Expose/Read/Demodulate for a 2nd rotation, adding to the previous results
Sum 2 pixels in spatial direction on chip => effective pixel size is 0.32 “x 0.32”
Raw data rate is 492 Kpixels in 3.6 sec = 137 Kpixels/sec
Maps area 1.6” wide in 18 sec, and 160” in 30 min

15

SP Observing Modes - 2
Dynamics Mode
Expose/Read/Demodulate for only 1 full rotation of waveplate
Optionally step the slit by 0.16”
Must limit spatial FOV to reduce data rate: maybe 32” typical slit length
For 32”along the slit, raw data rate is 192 Kpixels in 1.6 sec or 120 Kpixels/sec

Deep Magnetogram Mode
Expose/Read/Demodulate for many full rotations of waveplate
Goal is to detect weakest polarization signals possible
Ignore wrap-around of intensity and strong polarization signals
Downlink data with no compression to avoid artifacts from wrap-aroundboundaries
In any mode, Field-of-View and data rate can be restricted by sending to the MDP only spectrafrom a limited spatial portion of the slit

16

Spectro-Polarimeter (SP)Obtains spectra of two Fe lines at 630.15 and 630.25 nm andnearby continuum, with a 0.16 x 164 “ slit.
Spectra are exposed and read out continuously, 16 times per
rotation of the Polarization Modulator (PMU) (1.6 sec)
Raw spectra are added and subtracted onboard in real time todemodulate, forming Stokes I/Q/U/V.

I

Q

U

V

NS direction

164 arcsec
Spatial Sampling
0.16 arcsec

Spectral direction: resolution 0.0030 nm/sampling 0.00215 nm

SP maps of Sunspot Region

Q horizontal
component

Intensity

V verticalfield

U horizontal
component

Filtergraph Observables
Filtergrams
Broadband Filter Imager: all bands, only observable made by BFINarrowband Filter Imager: all lines & nearby continuum

Dopplergrams
Images of the Doppler shift of a spectral line => line of sight velocity
Derived from narrowband filtergrams at several wavelenghts

Longitudinal Magnetograms
Give the location, polarity and crude estimate of flux of magnetic fieldcomponents along the line-of-sight
Derived from narrowband filtergrams converted to Stokes I & V

Stokes Parameters I, Q, U, V
Analysis of IQUV at multiple wavelengths in a spectral line yields vector
magnetic field information (“vector magnetograms”)
I, Q, U, V images made onboard from narrowband filtergrams at different
polarization modulator positions
19

Filtergrams (NFI & BFI)
Shutter open/close always synchronized with Polarization
Modulator
Exposure times 0.1 - 1.6 sec in NFI, .03 - .8 sec in BFIFull readout in 3.4 sec, 2x2 summing in 1.7 sec
Partial readout possible for faster cadence & reduced data
volume: several discrete sizes from 192 to 2048 rows
Reconfigure time (filterwheels, TF) < 3 sec
No onboard processing in FPP, optional data compression in
MDP

20

Broadband Filter Imager (BFI)
Images at the highest possible spatial resolution andcadence(<<10 seconds) for accurate measurementsof horizontal flows, locations of magnetic features, anddetermination of surface temperature.

Red Boxes show Full FOV

Full FOV 218 x 109 “ (4Kx2K Pixels )0.0541“ pixel

Broadband Filter Imager (BFI)
Center

FWHM

Purpose388.35 nm
396.85 nm
430.50 nm
450.55 nm
555.05 nm
668.40 nm

0. 7 nm CN molecular band head: chromospheric network
0.3 nm Ca II H-line: magnetic elements in low chromosphere
0.8 nm CH G-band: magnetic elements, flow mapping
0.4 nm Blue continuum for irradiance: temperature
0.4 nm Green continuum
0.4 nm Red continuumSpectral Coverage Achieved byInterference Filters
G-band image expected from FPP

CaH 393.3 nm Image
from BFI System(The fine line in center is caused by missing line pair. The circular cutoff is caused by
the CCD cold trap. The cold trap has since been replaced and cutoff now longer occurs)Narrowband Filter Imager (NFI)
Provides intensity, Doppler, and Stokes polarimetry
imaging with good spectral resolution ( <0.01 nm)
FOV’s and spatial sampling are selectable
Blue Boxes indicate full FOV

Narrowband Filter Imager (NFI)
Spectral lines in Lyot filter
Ion

Wavelengthg eff

PurposeMg I b517.27 nm

1.71

Magnetograms and dopplergrams in low
chromosphereFe I

524.71 nm

2.00

PhotoMagnetograms

Fe I

525.02 nm

3.00

Line ratio Magnetograms with 525.06

Fe I

525.06 nm

1.50

Fe I

557.61 nm

0.00

Photospheric Dopplergrams

Na D

589.6 nm

1.50

Weak Fields - Chromospheric Fields

Fe I

630.15 nm

1.67

Photospheric Magnetograms

Fe I

630.25 nm

2.50

Photospheric Magnetograms

Ti I

630.38 nm

0.92

Sunspot Umbra Magnetograms

Hα656.3 nm

Filtergrams and Dopplergrams

Hα 656.3 nm Image from NFI
System(Black band at bottom is cause by misalignment cause by instrument leg mounting.
This has been corrected. )Dopplergrams
Maps of line-of-sight component of velocity
Baseline is simplified version of algorithm used by MDI instrument on SOHO
Derive central wavelength from 4 images uniformly spaced in the line, F1 ... F4
R = (F1 + F2 - F3 - F4) / (F1 - F2 - F3 + F4)
Use 2 smart memories to make numerator & denominator
Velocity = V(R), implemented on the ground by lookup-table
Two wavelength dopplergrams possible for higher cadence

Best photospheric line is Fe I 557.6 (non-magnetic, g=0)1-sigma noise of 30 m/s with 4 images, 2x2 summing, 0.16” px, 0.2 sec exposure,Low chromospheric velocity measured in core of Mg I 517.3 line
Very dark line, but higher velocities expected
1-sigma noise ~ 100 m/s with 0.16” px, 1.6 sec exposures27

Quantitative Evaluation with Solar
Rotation
The data were obtained in April 19-20, 2005 at Palo Alto.
2x2 summing mode, 1Kx1K partial images
The solar diameter is around 600 pixels.
The Doppler velocity is evaluated along the latitude

Raw data of FG Dopplergram
Velocity index (R)FG Longitudinal Magnetogram
Constructed from multiple
NFI filtergrams in a magnetic
sensitive line
Onboard real-time processing
makes numerator &denominator
630.2 nm magnetogram with
1x1 summing has RMS noise
15of ~1 10 Mx/pixel

Map of Stokes V / Stokes I

Fe 630.2 nm Magnetogram from
NFI
Partial field images taken to rapidly
make image pairs in order tominimize seeing effects

Stokes Parameters
Shutterless imaging with FOV restricted by focal plane mask
0.1 sec exposure and readout time: IQUV all measured simultaneously
FOV = 8 x 164 for 0.08” pixels, 16 x 164 for 0.16” pixels
Processing in smart memories identical to that for SP, to make spatial maps of I,
Q, U, and V
0.2 sec exposure and readout time: I & Q or I & U, measured separately
FOV = 16 x 164 for 0.08“ pixels, 32 x 164 for 0.16” pixels
Measure I & Q first, then I & U by shifting phase of exposure wrt Pol. Mod.
0.4 sec exposure and readout time: I & V only
FOV = 32 x 164 for 0.08” pixels

Stokes Parameters using shutter
0.4 sec exposures possible for V, 0.2 sec for Q & U
Additional noise sources due to time between frames & cross-talk between
polarizations will appear31

Shutterless (I, Q, U, V)
2004/08/20 01:01 UT

2004/08/20 01:01 UT& (I, U, V)
2004/08/20 01:03 UT

Assembled Tunable FilterImage Stabilization System
The SOT ISS consists of correlation tracker (CT) in FPP
and tip-tilt mirror in OTA (CTM).
The CT is a separated system with its own special
processor and 50 x 50 pixel CCD.
The correlation tracker target is an 11 x 11“ region in
the target FOV.
The laboratory measured stability is < 0.02” for a 30
second period
Additionally the Solar-B attitude system tracks a target
continuously at the local speed of the solar differential
rotation.
NSequence Control and Compression
Sequence control of observations is managed by observing
tables in Mission Data Processor (MDP).
One table for filter observation, the other for SP observation
The table is the list of macro-commands for observables with time interval.

FPP science data can be compressed in MDP
To reduce the data volume in telemetry
MDP has an ASIC chip for 12bit JPEG/DPCM
Pixel data is bit-compressed from 16 bit-pixel to 12 bit; 8 look-up tables
12bit JPEG (DCT): lossy~3 bits/pixel for FG data
~1.5 bits/pixel for SP data
, when compression noise is comparable to photon noise level
12bit DPCM: lossless, 6-8 bits/pixel
Compression ratio depends on images and required quality

Data Recorder and Data Rates
Solar-B Data Recorder and Data Downlinks
Capacity: 8 Gbits
5.6 Gbits for FPP data with assumption of ~70% allocation.
4 Mbps high telemetry (X-band) downloads ~1.7 Gbits FPP data in
one station pass (10 min duration).

Allocated telemetry rate for FPP compressed data
Possible maximum rate ~1.3 Mbps (in nominal)~1.8 Mbps (in SOT dominant) ~70 min to occupy 5.6 Gbits in data recorder
The rest of the time is in idle.
Rate averaged per day
25.5 Gbits (3.2 Gbytes) in a day, assuming 15 downlinks in a dayor ~300 Kbps

Example Observation
Goal: The magnetic/dynamical nature of micro-flare associatedsmall emerging fields in AR.
Telemetry: 300 Kbps continuously for several days
SP observation
Fast mapping, 80” wide scanning, NS size = 80”, 0.32” resolution
One map completed every 15 min
Data size: 229 Kpixel every 3.6 sec.
Telemetry: 96 Kbps with 1.5 bits/pixel compression.

FG observation

G-band, 3 wavelengths in Hα, Longitudinal magnetogram, Dopplergram,repeated every ~ 45 seconds.
80”x 80” FOV, 0.08” resolution for G-band and magnetogram, 0.16” forHα and Dopplergram
Data size: 3.25M pixel every 45 seconds
Telemetry: 222 Kbps with 3 bits/pixel compression

Example Observation-Spicules
JOP 2b: by DePontieu (SOT/FPP), Landi (EIS), Weber (XRT)
Goal: Opposite polarities and reconnection at footpoints of
spicules, and their impact on the transition region and corona
Telemetry:~360 Kbps total for 4 hours on each target region

SP observation
Normal map mode, 1.9 x 64“ FOV, 60 second cadence
360 Kpixel every 5.0 sec, 72 Kbps at 1bit/pixel compression

FG observation

Longitudinal magnetogram & Dopplergram in both 630.25 (photosphere) and 517.3(low chromosphere) & 2 wavelengths in H-alpha every 30 sec
64 x 64“ FOV, 0.08” pixels, 215 Kbps at 1 bit/pixel compression

EIS observation
One wide slit exposure for coalignment, 5 x 70 “ rasters of spectra

XRT observation
LogT = 6.1 images at full resolution, 128 x 128 “ FOV, 30 second cadence
See the complete JOP description including the other instruments’ details at

http://hea-www.harvard. edu/solarb/documents/MODA/SOT/FPP Science Plan
Science objectives
A. The Origin and Dynamics of the Solar Magnetic Field
A.1 Large-scale active region structure and dynamics
A.2 Sunspot formation, dynamics, and decay
A.3 Small-scale magnetic fields

B. Magnetic Modulation of Solar Luminosity and Irradiance
B.1 Active region irradiance contributions
B.2 Photospheric network irradiance contributions
B.3 Physics of small-scale magnetic element irradiance
B.4 Chromospheric irradiance variations

C. Heating of the Upper Solar Atmosphere
C.1 Coronal heating
C.2 Spicules, jets, and microflares
C.3 MHD waves and atmospheric seismology
C.4 Connectivity of photospheric magnetic field to coronal structures

D. Flares and Transient Phenomena
D.1 Magnetic topology and evolution in flares
D.2 Prominences, filaments, and transient initiation
D.3 CME initiation and development
D.4 Photospheric and chromospheric response to flares

Each objective has one or more “Observing Programs” or “JOPs” assigned to it.

SOT/FPP Science Plan
Sample Abbreviated Observing Plan
A.1.a. Active region formation: The “flux history” of active regions
Scientific objective and requirement. The primary objective of this program is tomeasure the magnetic flux emergence and decay rates of one or more active regions. Thisrequires vector magnetic field maps of entire active regions (3 – 5 arcmin field-of-view)
over time periods of several days. Etc…
Target selection and FOV. The targets must be emerging active regions of moderate tolarge size on the eastern hemisphere within 60º longitude of the central meridian. This
allows tracking of the active region over an area on the disk without excessive line-of-sightangles to the magnetic field. The FOV must encompass the entire active region. Minimum
requirement: 2048x2048 center region of BFI/NFI for 164”x164” FOV.
Spatial resolution. 0.05 – 0.08” spatial resolution in BFI/NFI filtergrams. Chromosphericfiltergrams can be binned 2x2 for 0.16”. SP vector magnetogram resolution no more than0.5” over entire region; 0.3” for sub-region scans of sunspot formation and decay.
Duration and cadence. The active region should be tracked across the disk for at least 10
days. Cadence for filtergrams is one per minute. Cadence for vector magnetic field
mapping is one per orbit (approx. 90 minutes).

SOT/FPP Science Plan
Sample Abbreviated Observing Plan (cont.)
A.1.a. Active region formation: The “flux history” of active regions
SOT/FPP Observations.
Emergence phase
NFI:

Fe I 630.25nm Stokes-V magnetogram. Cadence 1min. 1x1bin: 0.08” pixels.
Fe I 557.6nm dopplergram. Cadence 2 min. 1x1 bin: 0.08” pixels.
Hα 656.3nm filtergram. Cadence 2 min. 2x2 bin: 0.16” pixels.

BFI:

Gband 430.5nm filtergram, cadence 1 min. 1x1bin: 0.05” pixels.

SP:

Fast map mode. 164”x320” (full slit scanned over 320”). 1000 spatial steps at
0.32” per step. Cadence 42 min. Repeat once per orbit.

Tracking phase
NFI:

Fe I 630.25nm Stokes-V magnetogram. Cadence 5 min. 1x1bin: 0.08” pixels.
Fe I 557.6nm dopplergram. Cadence 5 min.

etc.
XRT Observations.
EIS Observations.
Supporting Observations. Other space instruments, ground-based support, etc.
Database/Analysis requirements.

SOT/FPP Science Plan
Status of the SOT/FPP science plan
• Outline/basic structure is complete.
• Current format is Microsoft Word document.
• A few observing plans/JOPs completed.
• Many others need to be defined and completed.
• Future:• Web-based “Wiki” document will be installed at LMSAL by January 2006.
• Allows modification via web-browser by any and all Investigators andCollaborators.
• SOT/FPP Science Team Meeting in April at NAOJ