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CIS Calibrations

VIEWS: 6 PAGES: 23

									Status of CIS Calibration and Archival Activities

    Iannis Dandouras, Alain Barthe, Lynn Kistler, and the CIS Team




4th CAA Cross-Calibration Meeting          LPCE, Orléans, February 2007
                                Overview

• CODIF Calibration Status

• HIA Calibration Status

• HIA – WHISPER Cross-Calibrations

• Limitations in the accuracy of density and other moments derived from CIS

• CIS - CAA ICD Version 2: Evolution with respect to Version 1

• Software development for moments calculation

• Open Issues and Future Work
             CODIF (CIS-1) Calibration Files Updating
The CODIF calibrations updating is a complex
process. It involves :

 the determination of the start-MCP efficiency

 the stop-MCP efficiency

 the fraction of coincidences between the
“start” and the “stop” signal that also have a
single position signal, allowing thus to calculate
the total efficiency

 In addition, the efficiencies of the individual
anodes (for each 22.5° sector) have to be
cross-calibrated

 calibrations involve also separate efficiencies
determination for the four main ion species          Lynn Kistler
             CODIF Calibration Files Updating : status
• Complete updated CODIF calibration values set, for the High-Sensitivity side,
covering the period :

     sc1: from launch to Oct 2004 (when the instrument was switched off)

     sc3: from launch to December 2005

     sc4: from launch to January 2006

was delivered last October by Lynn Kistler and Chris Mouikis (UNH).

• Updates include:

     Extended time coverage (previous calibrations were valid until Oct. 2004)

     Revised O+ efficiencies

• Following format editing, merging and testing at CESR, it has now been inserted in
the reference CIS calibration files, and is available for retrieval by the CAA.

• Work in progress at UNH for updating the calibration values for the
Low-Sensitivity side (only sc4 during dayside constellation concerned).
CODIF Efficiencies for sc3 and sc4
CODIF sc4 H+ Anode Efficiencies
CODIF Relative Anode Efficiencies : sc4
                  CODIF Efficiencies Summary



• SC4 and SC3 efficiencies declining slowly.
    SC4 is now at ~10% of original efficiency.
    SC3 is at ~5%.
    Data returned still looks good.
• Anode differences also slowly changing
                 HIA (CIS-2) : Calibration Status

• MCPs in good shape.

• MCP efficiencies stabilised: very slow evolution since 2003.

• Slight rise of the MCP HV on sc1 and sc3, applicable from this week.

• Calibration files updated several times: step function introduced.

• Most recent calibration update : September 2005 [C. Vallat].

• Calibration updates implemented in the calibration files:
    valid until April 2005.
  HIA (CIS-2) Status :
MCP High Voltage Evolution


                             + Feb. 2007
                             HV increase
     HIA Calibration: LS side (Solar Wind)
 Comparison with the density derived from Whisper




                  HIA density slightly below whisper density
2001 JAN 15




                 HIA density slightly above whisper density
2001 FEB 23
         HIA Calibration: HS side (Magnetosheath)
      Comparison with the density derived from Whisper
                  S/C1                               S/C3


2001 JAN 14



                      HIA density slightly below WH. density



2001 FEB 23
                          HIA density slightly above WH.density

                                                       HIA saturation (SW)
Observations of a very dense population of locally accelerated
  thermal ionospheric ions in a region just adjacent to the
         magnetopause (on its magnetospheric side)

       Plasma Sheet                      Ionospheric
                                             Ions




                                      Sauvaud et al., 2001
   Low-energy (order 10 eV) ion flow in the magnetotail lobes




For ion flow energies much higher
   than the spacecraft potential




 For ion flow energy below Vsc

Wake formation around
   the spacecraft
                           Engwall et al., 2006
Low-energy (order 10 eV) ion flow in the magnetotail lobes




                                        RPA cutoff wrt Vsc
Limitations in the accuracy of density (and other moments)
                     derived from CIS
• Density provided by a particle instrument is not the total density, but an integral of
the particle counts in the instrument energy range:

     Underestimated density in the presence of cold plasma, below the
    instrument energy threshold, or of hot plasma above the instrument upper
    energy limit.

     Underestimated velocity, temperature and pressure in the presence of hot
    plasma above the instrument upper energy limit.

• Spacecraft charging to a positive floating potential further raises the detection
energy threshold, increasing the difference between real and measured densities.

• Measured particle counts are underestimated in case of detector saturation, in the
presence of high ion fluxes (dead time effects).
These are phase space dependent: the detector can be saturated in a limited
energy range and in a given solid angle.
Limitations in the accuracy of density and other moments
                 derived from CIS (cont.)
• Eventual instrument background counts due to penetrating particles, from the
radiation belts around perigee passes or during SEP events, can result in an
overestimation of the density calculated there.

• Density and velocity (Vz component) calculation results are sensitive to the
accuracy of corrections for detection efficiencies, for the different anodes
(anode cross-calibrations). Although these are taken into account in the calibration
files, the error bars become large and systematic errors are unavoidable in the
case of strong inhomogeneities between anode efficiencies (e.g. CODIF on sc3).

• Moments error bars are sensitive to counting statistics:
 error bars become large in the case of low counting rates.

• The entire velocity phase space, corresponding to the instrument energy domain,
is not covered during all modes. This can be the case during solar wind modes,
and some magnetosheath modes.
Limitations in the accuracy of density and other moments
                 derived from CIS (cont.)
• CIS is a versatile and very efficient instrument package, consisting of
 5 different and complementary sensors:

     CODIF – High Sensitivity side

     CODIF – Low Sensitivity side

     CODIF - RPA

     HIA – High Sensitivity side

     HIA – Low Sensitivity side

    Each of them has a different dynamic range, and is optimised for a different
    plasma regime.
    Otherwise a single sensor instrument would have been provided!
    The users should choose the appropriate sensor.
    Inaccurate results are unavoidable from the other sensors.
Limitations in the accuracy of density and other moments
                 derived from CIS (cont.)

• Presence of ions other than H+ in the HIA data results in underestimated densities
and overestimated temperatures and pressures.

• CODIF mass-separated data can suffer from spillover between neighbouring
mass channels (e.g. He++ contamination by H+).

• CODIF calibration work, for species other than H+, is constrained by the paucity of
periods during which the plasma is dominated by these minority species, and by
the absence of any cross-instrument calibration possibility.

• Random short-term fluctuations in the MCP efficiencies can be present, and are
almost impossible to correct for.

• Detector ageing comes with a degradation of the SNR.
Limitations in the accuracy of density and other moments
                 derived from CIS (cont.)
• Irreversible noise removal techniques should not be applied to the archival data.

• Operation incidents, watch-dog instrument resets etc. can result in incorrect
MCP HV values and/or discriminator level values for short periods, which reduce
the accuracy of the collected data.
These data are not removed (useful for qualitative analysis, boundary
identifications etc.), but are flagged in the Caveats.

• Calibration corrections are statistical.
Impossible to correct for every single event, with a reasonable manpower effort.
                    CIS - CAA ICD Version 2:
                 Evolution with respect to Version 1
• “Grouping together” of some of the CIS-CODIF Level 3 data products.

• Addition of new data products in particle phase space density units.

• Addition of a software package allowing the CAA user to read the CIS Level 3 CEF
files and interactively calculate partial or total moments of the ion distributions, for
selected energy and solid angle ranges. However, to allow “easy availability”,
CODIF pre-calculated moments are also provided.

• Addition of an appendix providing a CIS data selection guide for the CAA user.

• Addition of an appendix describing how raw instrument data are transformed in
various physical units, and how moments of the ion distribution functions are
calculated.

• Updated CIS Level 2 data products description.

• Updated “Points of Contact” and various minor updates.
      Software development for moments calculation
• Software modules developed (one for CODIF and one for HIA), allowing the
CAA user to interactively calculate partial (or total) moments of the ion
distributions, for selected energy and solid angle ranges.

• Software in C.
         Input: CIS CEF Level-3 files
         Output: CEF files.

• Software tested and validated for density and bulk velocity calculation.

• Currently under test for temperature and pressure calculation.

• Question to the project:

    Velocity coordinates transformation from pseudo-GSE to GSE
    or other systems. Software interfacing with attitude files.
                 Open Issues and Future Work


• Ready for data reprocessing.
 However, CIS-CAA ICD Version 2 should first be approved.

• Open issue: Caveats format definition.
 CIS caveats readily available in ASCII tabular format files
 (or as HTML files).

• Other future work:
Software to be developed for some secondary datasets
(selected events, monitor rates, 64 m/q …).

								
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