NHSC SPIRE Data School – Pasadena 28 th - 30 th June 2010 PACS page 1 SPIRE Imaging Fourier...

NHSC SPIRE Data School – Pasadena28th - 30th June 2010

PACS page 1

SPIRE Imaging Fourier Transform Spectrometer (FTS) Pipeline Data

Processing

Nanyao Lu (NHSC/IPAC)

PACS page 2 Nanyao Lu


List of Topics

• Overview of SPIRE (FTS) Spectrometer

• Overview of the FTS Pipeline



SPIRE SpectrometerFourier Transform Spectrometer (FTS): The entire spectral coverage of 194-671 micron is observed in one go!

(SMEC)

(194-313 um)

(303-671 um)



Two Bolometer Detector Arrays

194 – 313 microns 303 – 671 microns

Beam = 17”- 21” Beam = 29”- 42”



Observing ModesTelescope Pointing

Single Pointing

Raster

Spatial Sampling

Sparse (2 beam spacing)

Intermediate(1 beam spacing)

Full(1/2 beam spacing; Nyquist)

Spectral Resolution High: 0.04 cm-1 (1.2 GHz), R=1290 – 370, e.g., line fluxes.

Intermediate: 0.24 cm-1 (7.2 GHz), R = 210– 60.

Low: 0.83 cm-1 (25 GHz), R = 62 – 18, e.g., dust continuum.

High + Low: Both High and Low scans.

Note: Data sampling at 25μm in OPD; Nyquist wave num. = 200 cm-1

Spectral resolution depends on the scan length



From Interferogram to SpectrumInterferogram

Optical path difference (cm)

Sig

nal (

volts

) FourierTransform

Source Spectrum



List of Topics

• Overview of SPIRE FTS Spectrometer

• Overview of the FTS Pipeline



Level 1 products:• unmodified interfergrams• average spectrum (apodized)• average spectrum (unapodized)

Interferograms (stored in Level 1)

Level 0.5 products:• detector time lines • scan mirror time line• house keeping time lines

Spectrometer Pipeline Data Flow

SPIRE Common Pipeline

1. Modify Detector Timelines

2. Create Interferogram

3. Modify Interferogram

4. Fourier Transform

5. Modify Spectra (V → Jy)

6. Spectral MappingLevel 2 product: Spectral Cubes (still under development)



1st Level Deglitching

Remove Electrical Crosstalk

Clipping Correction

Time-domain Phase Correction

Bath Temperature Correction

Cross talk matrix

V(t)

V(t)

V(t)

V(t)

Step 1: Modify Timelines

V(t)

V(t)

Level 0.5 Timelines

Modified Level 0.5 Timelines

Non-linearity Correction

V(t)

Bolometer Nonlinearity Table

Bath temp. corr. product

Time constants





Clipping Correction



Cross talk matrix

V(t)

V(t)

V(t)

V(t)


V(t)

V(t)



V(t)

Bolometer Nonlinearity Table

Bath temp. corr. product

Time constants

Clipping Correction





Clipping Correction



Cross talk matrix

V(t)

V(t)

V(t)

V(t)


V(t)

V(t)

Level 0.5 Timelines



V(t)

Bolometer nonlinearity table

Bath temp. correction table

Time constants



Create Interferograms

Once time domain processing is complete, the detector signals and SMEC positions can be merged to create interferograms.

The created “unmodified” interferograms are also stored in Level 1 in case users want to do their own interferogram-to-spectrum process.

V(t)

Step 2: Create Interferograms

Level 0.5 Timelines

V(t)

Unmodified InterferogramsV(x)

(Stored in Level 1)

SMEC Positions

x(t')

PointingP(t'')



Telescope/SCAL/Beamsplitter Correction

Baseline Removal

2nd Level Deglitching

Phase Correction

(Default apodization)

V(x)

V(x)

V(x)

V(x)

Step 3: Modify Interferograms

V(x)

V(x)

(Level 1) Interferograms

Modified Interferogram Products (both unapodized and apodized)

Reference background interferogram

Nonlinear phase calibration table

Norton Beer Order-1.5 function



Telescope/SCAL/Beamsplitter Correction

Baseline Correction

2nd Level Deglitching

Phase Correction

(Default) Apodization

V(x)

V(x)

V(x)

V(x)

Step 3: Modify Interferograms

V(x)

V(x)

(Level 1) Interferograms

Modified Interferogram Products

Reference background interferogram

Nonlinear phase

Norton Beer Order-1.5 function



Fourier Transform

Apply the Fourier Transform to each interferogram to create a set of spectra for each spectrometer detector.

Step 4: Transform Interferograms

SpectraV(σ)

Modified Interferograms

V(x)



Spectral Averaging

Flux Conversion: V->Jy

Remove Optical Crosstalk

V(σ)

V(σ)

Step 5: Modify Spectra

I(σ)

I(σ)

Spectra

Level 1 Spectrum Products

Extended-source case volt-to-Jy factors(both unapodized and apodized)

Detector optical crosstalk matrix

Spectra are all in extended-source calibration at Level 1.



Spectral Averaging



V(σ)

V(σ)

Galaxy IC 342: SLW Channel Spectra

I(σ)

I(σ)

Spectra


Point-source case volt-to-Jy factors




Spectral Averaging



V(σ)

V(σ)

Galaxy IC 342: SSW Channel Spectra

I(σ)

I(σ)

Spectra


Point-source case volt-to-Jy factors




SpatialRegridding

V(t)

Step 6: Spatial Regridding (Level 1 to 2)

Level 1 Spectra

I(σ)

Level 2 Spectral CubeI(σ)

(Under development)

Level 1 Spectra

I(σ)

Level 1 Spectra

I(σ)

For all observing modes but the sparse spatial sampling mode, for which only a point-source spectrum is given at Level 2.



Caveats and Remarks• Noise doesn’t average down as 1/sqrt(n) after about n = 25 repeats

as a result of some systematic fringes.

• Flux calibration is accurate to 10-20% for SSW, ~30% for SLW.

• The background subtraction still uncertain below 25 cm-1 in SLW. So the continuum level could be off significantly there. However, line calibration Is not affected.

• Extended-source flux calibration provided for all detector channels in all observing modes. Additional point-source calibration is provided only for the central detectors (SSWD4 & SLWC3) in the sparse observing mode.

• Lines are usually unresolved, but have side lobes following a SINC function. A SINC function fit is required for total flux.



Residual Background in SLW



Reprocess your FTS Observations• You probably want to use data processed with the latest

calibration files.

• A modified HIPE 4 pipeline script is available at ~/scripts_readonly/SPIRE/spec/SPIRE_spec_SOF1_pipeline_hipe4_modified.py,

which you can use to reprocess your data with any of the following options:

• Use the latest calibration files (i.e., spire_cal_4_0).• Only process the central detectors (to speed up data

processing & to avoid overloading your computer memory).• Using a user-supplied interferogram for telescope/sky

background subtraction.



Final Spectra are great!

SPIRE FTS SOF1 Pipeline and Calibration Files Trevor Fulton

25



You can play with FTS spectrum of Mrk 231


26

(Van der Werf etal 2010)



You can play with FTS spectrum of Mrk 231


27

There are 3 files in ~/scripts_readonly/spire/spec:

>>> Copy the following 2 files fro there to your home directory:SPIRE_spec_SOF1_pipeline_hipe4_modified.pySCalSpecInterRef_CR_nominal_20050222_50002972_average_fourier_ALL_DETS.fits

>>> Copy the following data to your ~/.hcss/lstore/ and then untar it there:50002975.tar

NHSC SPIRE Data School – Pasadena 28 th - 30 th June 2010 PACS page 1 SPIRE Imaging Fourier...

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