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.