FM ILT Spectrometer Wavelength Calibration Status Report H. Feuchtgruber, R. Vavrek

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FM ILT Spectrometer Wavelength Calibration
Status ReportH. Feuchtgruber, R. Vavrek
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Overview of Measurements (1)

• Nov/Dec 2006 FMILT1
• - 2 short scans of water vapour cell and few
  laser lines
• measured (initial calibration done, report
  available)
• Mar 2007 FM ILT2
• - Measured FIR-Laser lines µm (5 days)
• - CH3OH 70.511638, 77.405660, 96.522408,
  118.834107,
• 163.03352, 170.57637 x 5 chopper angles
• - 13CH3OH 115.82324, 203.63577 x 5 chopper
  angles
• - CH318OH 134.6-0.1, 162.647, 219.801 x 5
  chopper angles
• - Gas cell measurements (with Kapton foil)
• - H2O (27 hours)
• One Measurement consists of full scan
  vapour full scan vacuum
• Filter A (C0.1pF(blue), 1pF(red) x 3
  chopper angles
• Filter B (C0.1pF(blue), 0.2pF(red) x
  3 chopper angles
• - CO (3 hours)
• Grating range scan pair vacuum CO gas at
  1 chopper angle

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Overview of Measurements (2)

• June 2007 FMILT3
• Gas cell measurements (without Kapton foil)
• - H2O (9 hours)
• One Measurement consists of full scan
  vapour full scan vacuum
• Filter A (C0.1pF(blue), 1pF(red) x 1
  chopper angle
• Filter B (C0.1pF(blue), 0.2pF(red) x 1
  chopper angle

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FIR Laser Setup

• TUFIR window
• Extended, but structured source
• with substantial contrast
• Substantial laser power variation
• (recorded within setup)
• Scan parameters
• Range 100-120 steps (updown)
• Stepsize 100
• Readouts per ramp 64
• Ramps per position 3

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Gas Absorption Setup

• Focus window
• Extended and controlled background source
• Source T600C (H2O) and T400C (CO)
• Absorption path 56cm
• p 9mBar (H2O) and p70mBar (CO)
• Scan parameters
• - Range 32000-1064000
• - Stepsize 200
• - Readouts per ramp 64
• - Readouts per position 3

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Calibration Method (1)
?? ????0.6253 gLHe117.175µm n1,2,3
pix1..16
? ?0 (p1-1)(gratpos/dgrat)
p2(gratpos/dgrat)2 p3(gratpos/dgrat)3 with
dgrat 23301 steps/?
dpixn constant(n) n1,2,3,2
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Calibration Method (2)

• Begin with calibration from FILT1 (few lines
  measured only)
• Calculate up/down corrected and divided spectra
  (gas/vacuum) for each pixel
• Fforeground(?) Tgas(?)Fbackground(?)
• Ratio
• Fforeground(?)
  Fbackground(?)
• with Fforeground (?) ? (2050) x Fbackground
  (?)
• Calculate model spectra (at expected PACS
  spectral resolution) for the wavelength range
  under investigation and define spectral intervals
  for correlation analysis
• Determine ?-calibration offsets for each interval
• Store 3rd order polynomial parameters fitted to
  offsets vs. (gratpos/dgrat) for each pixel
• ?new ?old polynomial fit
• Iterate previous steps (at least twice)

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Results

• A semi-automatic method to calibrate each pixel
  in each array is now available
• ?-calibration 3rd order polynomials for all
  individual spectrometer pixels have been derived
• Separate sets of polynomials have been calculated
  for the 3 main PACS spectrometer bands and the
  extra band (2nd order via filter A 54-73µm)
• CO line positions are compliant with calibration
  based on water
• Laser positions largely compliant with
  calibration, however few
• single pixels show still some significant
  deviations ? still to be corrected in a case by
  case analysis
• Laser lines may show peak-center variations due
  to actual position of laser spots within the
  slit.
• This is the initial uplink calibration for flight
  

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Data Quality (1)
single pixel
Typical data used during correlation analysis
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Data Quality (2)
single pixel
rebinned module
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Accuracies

• PCD V8.0 (sec. 4.2.1)
• Required accuracy
• Peak position to within 10-20 of a spectral
  resolution element
• In general the requirement is met throughout all
  bands however at band borders, due to leakage
  effects and lower S/N the calibration accuracy
  (in terms of s over all pixels) is closer to 20
  of a spectral resolution element, while in band
  centers, s values even better than 10 are
  obtained.
• sstdev(all_pixels residual ?-shift vs. model)
• Absolute verification against Laser and CO lines
• Relative verification by combining all pixels
• Be aware relative position of point sources
  within slit can have significant effect

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Remarks

• Depth of grating scans (normalized to line
• scan AOT)3rd order (2.5h), 2nd order (2.5h),
  
• 2nd order (2.8h),1st order (3.6h)
• (time1st 58steps 0.75sec 2updown
  3numres
• 2vapvac 25modules / 3600sec)
• HDO lines are detected (abundance 3e-4 partial
  
• pressure 2.7e-6 bar)
• CO spectra show residual lines from water
  contamination

Faintest lines 3e-18W/m2
n3, 2
n2
n1
C1pF
C0.2pF
C0.1pF
Leak models
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Remarks

• Depth of grating scans (normalized to line scan
  AOT)3rd order (2.5h), 2nd order (2.5h),
• 2nd order (2.8h),1st order (3.6h)
• (time1st 58steps 0.75s 2updown 3numres
  2vapvac 25modules / 3600s)
• HDO lines are detected (abundance 3e-4 partial
  pressure 2.7e-6 bar)
• CO spectra show residual lines from water
  contamination

Faintest lines 3e-18W/m2
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Expected Line centers and slit widths overplotted
Verification with Laser Lines
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Next Steps / Open Work

• Investigate/recalibrate few outlying pixels found
  during verification against Laser lines. The
  reason is essentially the poor S/N in the
  measurements during FM ILT 2.
• Calibrate L/L chopper throws, spot checks
  indicate that there is no significant change in
  calibration
• Provide Report and Calfiles (version as of this
  report provided for PACS spectrometer pipeline)
• Check calibration and eventually recalibrate for
  FMILT 3 measurements

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Instrumental Profile (1)

• For more details see report by R. Vavrek

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Instrumental Profile (2)
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Wavelength Calibration in Flight (1)

• Observing modes
• Use standard SpecRangeScan AOT
• Use Wave_Cal mode with pointing request
• Suitable target list
• - PICC-ME-TN-013, Use of late type stars for
  PACS wavelength calibration, (D. Lutz)
• Photometric and Spectroscopic Calibration of
  Herschel Instruments with Planets and
  Satellites, (Th. Encrenaz, R. Moreno, A.
  Coustenis)
• Uranus(H2O), Neptune(H2O, CO), Saturn(H2O, NH3,
  PH3)
• Jupiter (H2O, NH3, PH3 fills entire 5x5 field
  of view !)

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Wavelength Calibration in Flight (2)
Start PV
Start Routine Ops
Target visibilities (HSPOT)