pacs icc meeting #291/2 oct 2007 wavelength calibration1 fm ilt spectrometer wavelength calibration...
DESCRIPTION
PACS ICC Meeting #291/2 Oct 2007 Wavelength Calibration3 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 (C=[0.1pF(blue), 1pF(red)] x 1 chopper angle Filter B (C=[0.1pF(blue), 0.2pF(red)] x 1 chopper angleTRANSCRIPT
PACS ICC Meeting #29 1/2 Oct 2007
Wavelength Calibration 1
FM ILT Spectrometer Wavelength Calibration
Status ReportH. Feuchtgruber
PACS ICC Meeting #29 1/2 Oct 2007
Wavelength Calibration 2
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;- CH3
18OH: [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 (C=[0.1pF(blue), 1pF(red)] x 3 chopper angles
Filter B (C=[0.1pF(blue), 0.2pF(red)] x 3 chopper angles - CO: (3 hours) Grating range scan pair: vacuum + CO gas at 1 chopper angle
PACS ICC Meeting #29 1/2 Oct 2007
Wavelength Calibration 3
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 (C=[0.1pF(blue), 1pF(red)] x 1 chopper angle Filter B (C=[0.1pF(blue), 0.2pF(red)] x 1 chopper angle
PACS ICC Meeting #29 1/2 Oct 2007
Wavelength Calibration 4
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
(up&down) Stepsize: 100 Readouts per ramp: 64 Ramps per position: 3
PACS ICC Meeting #29 1/2 Oct 2007
Wavelength Calibration 5
Gas Absorption Setup• Focus window• Extended and
controlled background source
• Source T=600°C (H2O) and T=400°C (CO)
• Absorption path ~56cm
• p= 9mBar (H2O) and p=70mBar (CO)
• Scan parameters- Range: 32000-1064000- Stepsize: 200- Readouts per ramp: 64- Readouts per position: 3
PACS ICC Meeting #29 1/2 Oct 2007
Wavelength Calibration 6
Calibration Method (1)
=; ==0.6253; gLHe=117.175µm; n=[1,2,3] ; pix=[1..16]
= 0 + (p1-1)*(gratpos/dgrat) + p2*(gratpos/dgrat)2 + p3*(gratpos/dgrat)3
with dgrat = 23301 [steps/]
δpixn = mean[δpixn,FILT1(module)]
PACS ICC Meeting #29 1/2 Oct 2007
Wavelength Calibration 7
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(λ) + Tgas(λ)*Fbackground(λ)Ratio = Fforeground(λ) + Fbackground(λ)
with Fforeground (λ) (20…50) x Fbackground (λ)
• Calculate model spectra (at expected PACS spectral resolution) for the wavelength range under investigation and define spectral intervals for correlation analysis
• Determine λ-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)
PACS ICC Meeting #29 1/2 Oct 2007
Wavelength Calibration 8
Results• A semi-automatic method to calibrate each pixel in each
array has been developed• λ-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 fewsingle pixels show still some significant deviations 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
PACS ICC Meeting #29 1/2 Oct 2007
Wavelength Calibration 9
Data Quality (1)
Typical data used during correlation analysis
single pixel
PACS ICC Meeting #29 1/2 Oct 2007
Wavelength Calibration 10
Data Quality (2)
single pixelrebinned module
PACS ICC Meeting #29 1/2 Oct 2007
Wavelength Calibration 11
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 σ over all pixels) is closer to 20% of a spectral resolution element, while in band centers, σ values even better than 10% are obtained. σ=stdev(all_pixels residual λ-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
PACS ICC Meeting #29 1/2 Oct 2007
Wavelength Calibration 13
• 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
Remarks
PACS ICC Meeting #29 1/2 Oct 2007
Wavelength Calibration 15
Verification with
Laser Lines
Expected Line centersand slit widths overplotted
PACS ICC Meeting #29 1/2 Oct 2007
Wavelength Calibration 16
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
PACS ICC Meeting #29 1/2 Oct 2007
Wavelength Calibration 17
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 !)
PACS ICC Meeting #29 1/2 Oct 2007
Wavelength Calibration 19
Wavelength Calibration in Flight (2)
• Target Visibilities in their 1st two windows (HSPOT):
Start PV
Start Routine Ops
Mars 18-Aug-09 – 9-Dec-09