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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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