Difference between revisions of "HFI-Validation"

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(Expected systematics and tests (bottom-up approach))
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* Random Telegraphic Signal (RTS) or Popcorn Noise - Some channels were occasionally affected by what seems to be a baseline which abruptly changes between two levels, which has been variously called popcorn noise or random telegraphic signal. These data are usually flagged. This is described in [[TOI_processing#Noise_stationarity|the section on noise stationarity]] and [[#RTS_noise|the section on Random Telegraphic Signal Noise]]
 
* Random Telegraphic Signal (RTS) or Popcorn Noise - Some channels were occasionally affected by what seems to be a baseline which abruptly changes between two levels, which has been variously called popcorn noise or random telegraphic signal. These data are usually flagged. This is described in [[TOI_processing#Noise_stationarity|the section on noise stationarity]] and [[#RTS_noise|the section on Random Telegraphic Signal Noise]]
 
* Jumps - Similar to but distinct from popcorn noise, small jumps were occasionally found in the data streams. These data are usually corrected. This is described in [[TOI_processing#jump_correction|the section on jump corrections]].  
 
* Jumps - Similar to but distinct from popcorn noise, small jumps were occasionally found in the data streams. These data are usually corrected. This is described in [[TOI_processing#jump_correction|the section on jump corrections]].  
* 4 K Cooler-Induced EM Noise - The 4 K cooler induced noise in the detectors with very specific frequency signatures, which is filtered. This is described in {{PlanckPapers|planck2013-p03|1|the 2013 HFI DPC Paper}}, [[#4K_lines_Residuals|the section below on 4K line residuals]], and their stability is discussed in [[TOI_processing#4K_cooler_lines_variability|the section on 4K cooler line stability]].
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* 4 K Cooler-Induced EM Noise - The 4 K cooler induced noise in the detectors with very specific frequency signatures, which is filtered. This is described in {{PlanckPapers|planck2013-p03|1|the 2013 HFI DPC Paper}}, [[#4K_lines_Residuals|the section below on 4 K line residuals]], and their stability is discussed in [[TOI_processing#4K_cooler_lines_variability|the section on 4 K cooler line stability]].
 
* Compression - Onboard compression is used to overcome our telemetry bandwidth limitations. This is explained in {{PlanckPapers|planck2011-1-5}}.  
 
* Compression - Onboard compression is used to overcome our telemetry bandwidth limitations. This is explained in {{PlanckPapers|planck2011-1-5}}.  
 
* Noise Correlations - Correlations in noise between detectors seems to be negligble but for two polarization sensitive detectors in the same horn. This is discussed in {{PlanckPapers|planck2013-p03e|1|the 2013 HFI Cosmic Ray Removal paper}}.
 
* Noise Correlations - Correlations in noise between detectors seems to be negligble but for two polarization sensitive detectors in the same horn. This is discussed in {{PlanckPapers|planck2013-p03e|1|the 2013 HFI Cosmic Ray Removal paper}}.
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# The official map-making is run on those processed timelines using the same parameters as for real data;  
 
# The official map-making is run on those processed timelines using the same parameters as for real data;  
  
This Desire simulation pipeline allows to explore systematics such as 4K lines or Glitches residual after correction by the official TOI processing, as described below.
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This Desire simulation pipeline allows to explore systematics such as 4 K lines or Glitches residual after correction by the official TOI processing, as described below.
  
 
==Simulations versus data==
 
==Simulations versus data==
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===1.6K and 4K stage fluctuations===
 
===1.6K and 4K stage fluctuations===
  
The 4K and 1.6K stages are thermally regulated. The level of (controlled) fluctuations is less than 20uK/sqrt(Hz) above the spin frequency (and below 0.2 Hz) for the 4K stage and 10uK/sqrt(Hz) for the the 1.6K stage. Using a typical coupling coefficient of 150 fW/K_4K, this translates into a noise of 3 aW/sqrt(Hz). This is 4% of the bolometer noise variance (with a NEP of typically 15aW/sqrt(Hz)), and is thus negligible.
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The 4 K and 1.6 K stages are thermally regulated. The level of (controlled) fluctuations is less than 20uK/sqrt(Hz) above the spin frequency (and below 0.2 Hz) for the 4 K stage and 10uK/sqrt(Hz) for the the 1.6K stage. Using a typical coupling coefficient of 150 fW/K_4K, this translates into a noise of 3 aW/sqrt(Hz). This is 4% of the bolometer noise variance (with a NEP of typically 15aW/sqrt(Hz)), and is thus negligible.
  
  
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The 4 K lines are the 4 K cooler induced noise in the detectors with very specific frequency signatures. They are filtered and corrected during the TOI-processing. The efficiency of this correction has been studied using two types of simulations at 143GHz: <tt>Yardstick</tt> and <tt>Desire</tt> simulations.
 
The 4 K lines are the 4 K cooler induced noise in the detectors with very specific frequency signatures. They are filtered and corrected during the TOI-processing. The efficiency of this correction has been studied using two types of simulations at 143GHz: <tt>Yardstick</tt> and <tt>Desire</tt> simulations.
  
The <tt>Yardstick</tt> simulations have explored the impact of 4K lines residuals on CMB signal only, by adding a 4K lines pattern on the CMB TOIs, and by applying the same module of correction as used in the TOI-processing. The impact on the CMB power spectrum has been estimated by comparing the spectra obtained on data without 4 K lines and data with corrected 4K lines.
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The <tt>Yardstick</tt> simulations have explored the impact of 4 K lines residuals on CMB signal only, by adding a 4 K lines pattern on the CMB TOIs, and by applying the same module of correction as used in the TOI-processing. The impact on the CMB power spectrum has been estimated by comparing the spectra obtained on data without 4 K lines and data with corrected 4 K lines.
  
The end-to-end <tt>Desire</tt> simulations include a complete sky (i.e. CMB, Galaxy and point sources) and the complete TOI-processing on the simulated data. The analysis and comparison is then performed on the maps directly and on the power spectra. It has been checked that the 4K lines modeling inputs used in the two sets of simulation are in agreement between them and with in-flight data. Those simulations have been performed on the full 143GHz channel, i.e. 12 detectors, and the full nominal mission range.
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The end-to-end <tt>Desire</tt> simulations include a complete sky (i.e. CMB, Galaxy and point sources) and the complete TOI-processing on the simulated data. The analysis and comparison is then performed on the maps directly and on the power spectra. It has been checked that the 4 K lines modeling inputs used in the two sets of simulation are in agreement between them and with in-flight data. Those simulations have been performed on the full 143GHz channel, i.e. 12 detectors, and the full nominal mission range.
  
[[Image:4Klines_expla.png|Simulation of 4 K Lines residuals on Power Spectra|center | thumb|800px|Power Spectra with 4K lines before and after correction by the TOI-Processing.]]
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[[Image:4Klines_expla.png|Simulation of 4 K Lines residuals on Power Spectra|center | thumb|800px|Power Spectra with 4 K lines before and after correction by the TOI-Processing.]]
  
  
Both analysis converge to show that the 4 K lines residual represent 2% to 2.5% maximum of the noise level at particular ell values affected by the 4K lines (such as ell=1800). These residuals are well below the one-sigma discrepancy of the noise itself at the same particular ell values.  
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Both analysis converge to show that the 4 K lines residual represent 2% to 2.5% maximum of the noise level at particular ell values affected by the 4 K lines (such as ell=1800). These residuals are well below the one-sigma discrepancy of the noise itself at the same particular ell values.  
  
Hence the 4K lines residuals are negligible. Nevertheless, the correlation between the 4K lines and the ADC correction discussed in {{PlanckPapers|planck2013-p03}}{{P2013|6}} may have an impact on the gain variation estimates at the end of the processing. This has still to be quantified.
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Hence the 4 K lines residuals are negligible. Nevertheless, the correlation between the 4 K lines and the ADC correction discussed in {{PlanckPapers|planck2013-p03}}{{P2013|6}} may have an impact on the gain variation estimates at the end of the processing. This has still to be quantified.
  
 
===Saturation===
 
===Saturation===

Revision as of 16:53, 29 January 2015


The HFI validation is mostly modular. That is, each part of the pipeline, be it timeline processing, map-making, or any other, validates the results of its work at each step of the processing, looking specifically for known issues. In addition, we do additional validation with an eye towards overall system integrity by looking at generic differences between sets of maps, in which most problems will become apparent, whether known or not. Both these are described below.

Expected systematics and tests (bottom-up approach)[edit]

Like all experiments, Planck/HFI had a number of "issues" which it needed to track and verify were not compromising the data. While these are discussed in appropriate sections, here we gather them together to give brief summaries of the issues and refer the reader to the appropriate section for more details.

Generic approach to systematics[edit]

This section is Under Construction


References[edit]

(Planck) High Frequency Instrument

random telegraphic signal

Cosmic Microwave background

[LFI meaning]: absolute calibration refers to the 0th order calibration for each channel, 1 single number, while the relative calibration refers to the component of the calibration that varies pointing period by pointing period.

analog to digital converter