SOHO Joint Observing Plan #4
INTERCALIBRATION 1
Author(s): R.A.Harrison (CDS), K, Wilhelm and U.Schühle (SUMER),
J.Kohl (UVCS), J.-P.Delaboudiniere (EIT), SIC Working Group.
Progress:
Draft Scheme February 15 1994
Discussion at SPWG/SICWG June 13/14 1994
Detailed Plan June 21 1994
Distributed to PI Teams June 22 1994
Revised after SUMER Input August 10 1994
Re-Distributed to PI Teams August 12 1994
Minor Revisions Nov 4/24 1994
CDS ID: ICAL1
Objective: Cross calibration of CDS-GI/CDS-NI/SUMER/UVCS and EIT
Scheme: All four instruments are directed at the same location on the solar
disc and wavelength bands are selected which are appropriate for
cross-calibration. The following considerations are taken into account:
A large co-incident field of view is required to ensure good co-registration
and significant spatial overlap - yet it must be small enough to be produced
relatively quickly.
The wavelength overlaps are the following: (1) CDS-GI and CDS-NI =
310-346Å, (2) CDS-NI and SUMER = 517-633Å - specifically the He I
584.33Å and Mg X 609.79Å lines, (3) CDS-GI and SUMER =
662-787Å - specifically the Ne VIII 770.41Å line, (4) CDS-GI and
EIT = 171, 195, 284 and 304Å, (5) CDS-NI and UVCS = 521, 610,625Å,
(6) SUMER and UVCS = 1216, 1242, 1032 and 1037Å.
Exposure times should be chosen to produce 10% counting statistics or better
(counts per pixel or order 100). For CDS, for the lines given below, this
translates to an exposure time of 20 Seconds.
The preferred target area, driven by UVCS, is on the disc, between 12 and 15
arcminutes from Sun centre. Presumably the target area should be quiet Sun.
CDS cannot perform rasters in GI and NI simultaneously. Therefore, CDS will
operate in phases, with phase 1 in NI, phase 2 in GI, with both repeated
several times.
We should minimise the number of wavelength ranges viewed by SUMER, to
minimise refocusing operation. Two bands should be sufficient. The SUMER bands
are of width 40Å for first order and 20Å for second order.
Specific Wavelength Selection
CDS-GI = Full wavelength ranges - 155-224Å, 261-346Å,
395-496Å, 662-787Å
CDS-NI = Mg VIII 313.73Å, 315.02Å, 317.01Å, Fe XIII
320.80Å, Fe XV 321.78Å, 327.02Å, Fe XIV, 334.17Å, Fe
XVI 335.40Å, Si IX 345.13Å, Si XII 520.67Å, He I
584.33Å, Mg X 609.79Å, Mg X 624.94Å
SUMER = Three bands - 1 centred on He I 584.33Å and Mg X 609.79Å
for the SUMER/CDS-NI calibration and Ne VII 770.41Å for the SUMER/CDS-GI
calibration.
UVCS = H I 1216Å, Fe XII 1242Å, O VI 1032,1037Å, Si XII
499,521Å, Mg X 610,625Å
EIT = All four bands - 171, 195, 284, 304Å
Pointing
All instruments should be directed to a quiet Sun area with rasters/fields of
view centred on a region between 12 and 15 arcminutes from Sun centre.
Operating Details
- CDS
- Phase 1: Use NIS with 4x240 arcsec slit over 15 locations - total area 1x4
arcmin. Use wavelength selection given above. Exposure time of 80 sec at each
of the 15 exposures - total duration 20 min. Data extraction from 13 windows
defined by lines above - 15 pixels across each, i.e. 13 x 120 x 15 x 16 bits at
10kb/s over 80 sec - only uses half of standard telemetry rate. No data
compression required.
- Phase 2: Use GIS with 4x4 arcsec slit over 8x8 locations - total area 32x32
arcsec. Use wavelength selection given above. Exposure time of 20 sec at each
of the 64 locations - total duration 21.3 min. Data extraction - 2048 pixels x
4 bands x 16 bits at 10kb/s over 20 sec. No data compression required.
Observation consists of: Phase 1, Phase 2, Phase 1, Phase 2, Phase 1, Phase 2,
Phase 1, Phase 2
Total duration: 4x20min + 4x21.3min +20% overhead = 198.2 min.
- SUMER
- Use 1x300 arcsec slit over 80 locations to form 61x300 arcsec image overlying
CDS 60x240 arcsec image. Step size = 0.76 arcsec with 7.5s accumulation at each
location. Total duration per raster of 600s.
- Phase 1: (a) Two raster scans with wavelength ranges centred on He I
584.33Å (pixel 890) and Mg X 609.79Å (pixel 910), respectively, for
CDS cross-calibration, or (b) He I and H I 1215.67Å (pixel 1008), for
UVCS cross calibration, or (c) He I and Fe XII 1242.01Å (pixel 360) for
UVCS cross calibration. Each of duration 600s - 1200s total.
- Phase 2: Two scans on one wavelength range, centred on Ne VIII 770.41Å
(pixel 140), each at 600s - 1200s total.
Observations consists of Phase 1a, Phase 2, Phase 1b, Phase 2, Phase 1a, Phase
2, Phase 1c, Phase 2, matching the CDS NI-GI operation. Total duration = 8 x
1200 sec = 160min without overheads.
- EIT
- Extract 50x100 pixels centred on CDS field of view - i.e. with 2.6 arcsec
pixels, a 2.2x4.3 arcmin field compared to the CDS 1x4 arcmin field.
Accumulation time of 20 Sec. Use all four bands. At 1 kb/s, 5000 pixels of 16
bits = 80 sec to extract data, i.e. 100 Sec cadence. Extract series of 120
images co-incident with the CDS/SUMER observations. Total duration - 200 min.
- Correction: Since EIT and LASCO compress in fixed, 32 x 32 pixel
blocks, it is more efficient to read out the EIT camera in blocks of that
size. Thus, the EIT plan could be to read out 64 x 96 pixels (166 x 250 arc
sec, or 2.77 x 4.16 arc min), in order best to match the CDS field of
view. Since the EIT pixel blocks will be fixed with respect to the CCD,
however, it is more likely that EIT will have to read out 96 x 128 pixels
(250 x 330 arc sec, or 4.16 x 5.55 arc min), in general, to include all of the
CDS field of view for this JOP. Including camera prep, exposure, readout,
compression with the Rice and 10:1 ADCT algorithms, each bandpass should take
about 40 s of LASCO/EIT resources (including telemetry at 5.2 kbps), or 2
min 40 s for all four bandpasses. Assuming that we can do so without
interrupting the LASCO/EIT synoptic program, we could run this program about
once every ten minutes, or 16 times within the 160 m duration of the JOP,
without using more than EIT's 20% of LASCO/EIT resources. (J.B. Gurman,
1994/11/22)
- UVCS
- Use 7 arcsec slit. Raster over 10 steps of 7 arcsec width. Raster centred
on CDS 60 x 240 arcsec field. Expose for 30 sec at each of the 10 locations.
Total duration of raster - 300 sec. Perform 3 times with different wavelength
selections: Phase 1 - include 1216Å, Phase 2 - include 1238, 1242Å
(Ly alpha channel), 1032, 1037, 1085Å (O VI channel), Phase 3 - 521,
610, 625Å. Repeat cycle 10 times = 150 min.