Data Set Overview
  =================
     This data set consists of all of the ion moments data generated from
     the Cassini Plasma Spectrometer (CAPS) ion mass spectrometer
     singles or time-of-flight uncalibrated data.

     The data set contains the derived ion moments data as follows:
     Ion Moments (ION_MOMT)
        Density, Temperature, Average Flow Speed, Average Flow Velocity
        Ions included are H+, H2+, and W+ (water group ions: O+, OH+, H2O+)

     The uncalibrated data were acquired in a mix of CAPS operating modes
     beginning with the first instrument checkout in January 1999 and
     containing throughout the Cassini Tour and through the end of prime
     mission.  The data set covers the time period from 1999-004T03:07:47
     UT until end of prime mission (July 2008).  In addition, it will cover
     data received during extended missions.  Sampling rates were variable
     and depended upon the downlink capabilities and other activities
     on-board.

     For times when CAPS is not producing data due to being turned off or
     due to communication issues, the data set will not contain data.

     Additionally, there will be no data during times when the calculations
     are not possible.

  ION Moment File Discussion
  ==========

     The data provided in this file are the moments of the ion distribution
     (density, temperature, and flow velocity) derived from measurements
     from the CAPS/IMS (Ion Mass Spectrometer) [YOUNGETAL2004].  The final
     adopted geometric factors, efficiencies, and other relevant instrument
     parameters used to derive these moments are available in the CAPS PDS
     User's Guide [WILSONETAL2012] and are slightly different than those
     used in the study of Thomsen et al. [THOMSENETAL2010].  The final
     values are based on calculations, laboratory calibrations, simulations,
     and comparison of in-flight data with measurements from other
     instruments, including CAPS/ELS (Electron Spectrometer [LEWISETAL2008,
     LEWISETAL2010]) and RPWS (Radio and Plasma Wave Investigation
     [GURNETTETAL2004]).

     When the Ion Method Flag is 1, i.e., numerical integration of the
     Singles (SNG) measurements, the partition of SNG counts into three
     different species bins (H+, H2+, W+) is based on concurrent
     measurements of the ion composition available from the Time-of-Flight
     (TOF) data product from the same instrument (W+ represents the sum
     of the 'water-group' ion species O+, OH+, H2O+, and H30+).  This
     partition and the numerical integration algorithm are described in
     detail in Thomsen et al. [THOMSENETAL2010] and Thomsen and Delapp
     [THOMSENETAL2005].  While the calculation of the moments (n,T,V) is
     is done independently for each species [THOMSENETAL2010], for the PDS
     submission we report only a single velocity vector, which is
     calculated as a mass- and density- weighted average of the velocities
     derived for the three species:

       AveV = sum (m_i * n_i * V_i) / sum (m_i * n_i)  where i=H+, H2+, W+

             (note that the _ indicates that what follows is a subcript)

     and where m_i and n_i are the ion mass and density of the ith species
     (m_W+ is taken to be 16, although in practice it makes very little
     difference whether one takes either extreme, i.e., 16 or 19).  This
     weighting is based on our experience [e.g., THOMSENETAL2010] that the
     heavy-ion velocities are more reliable when they are available (hence
     the weighting by m_i), but if they are not well-determined due to low
     counts, the light-ion values are to be preferred (hence the weighting
     by n_i).  The reported temperatures represent averages of the values
     perpendicular and parallel to the magnetic field.

     Because the ion flows within the Saturnian magnetosphere are typically
     transonic, an accurate measurement of the plasma properties requires
     that the flow be in the field of view.  Analysis of CAPS measurements
     has determined that the magnetospheric flows typically lie near the
     corotation direction [e.g., THOMSENETAL2010].  Therefore, the PDS file
     includes a flag to tell whether or not the corotation direction lies
     within the CAPS FOV.  In addition, the numerical moments algorithm
     does not work if the spacecraft is rolling or if the instrument is not
     actuating.  Under such conditions, the moments are flagged as 'bad'.
     Therefore, there are three values for the quality flag: 'Not-bad;
     corotation direction in FOV', 'Not-bad; corotation direction not in
     the FOV', and 'Bad (s/c rolling and/or CAPS not actuating)'.

  Data
  ====

    The data are stored in multiple data files and have been organized
    in folders, first by higher order data type and then by year.  Each file
    contains a maximum of 24 hours of data.  Note that data is included in
    the file based on the start time, and not the end time of the data.
    Format of the data files can be found in the CAPS instrument archive
    specification [FURMANETAL2013].  The format can also be found in the
    .LBL files in the FM/HIGHERORDER/IONMOMT/YYYY specific directory,
    co-located with the data.

  Ancillary Data
  ==============

    Ancillary data can be found in the ANC data file provided with the
    CAPS UNCALIBRATED data set.

  References
  ========
    [FURMANETAL2005] CAPS standard data products and archive volume
      software interface specification, Version 1.9, JPL SIS ID:
      IO-AR-017, Southwest Research Institute, San Antonio, TX 78250,
      2005.

    [ARRIDGEETAL2009] The effect of spacecraft radiation sources on
      electron moments from the Cassini CAPS electron spectrometer,
      Planetary and Space Science, 57, 854-869,
      doi:10.1016/j.pss.2009.02.011, 2009.

    [GURNETTETAL2004] The Cassini Radio and Plasma Wave Investigation,
      Space Sci. Rev. 114, 395-463, 2004.

    [LEWISETAL2008] Derivation of density and temperature from the Cassini
      Huygens CAPS electron spectrometer, Planetary and Space Science, 56,
      901-912, doi: 10.1016/j.pss.2007.12.017, 2008.

    [LEWISETAL2010] The calibration of the Cassini-Huygens CAPS Electron
      Spectrometer, Plan. and Space Sci., 58, 427?436,
      doi:10.1016/j.pss.2009.11.008, 2010.

    [THOMSENETAL2005] Numerical moments computation for CAPS/IMS, Los
      Alamos National Laboratory Report LA-UR-05-1542, 2005.

    [THOMSENETAL2010] Survey of ion plasma parameters in Saturn's
      magnetosphere, J. Geophys. Res., 115, A10220,
      doi:10.1029/2010JA015267, 2010.

    [WILSONETAL2012] PDS User's Guide for Cassini Plasma Spectrometer
      (CAPS), 2012.

    [YOUNGETAL2004] Cassini Plasma Spectrometer Investigation,
      Space Sci. Rev. 114, 1-112, 2004.

Review
  ======
    These data have been reviewed by the instrument team and are of the
    highest quality that can be generated at this time. Science results
    based on these data have been published in several journals (Science,
    Nature, JGR, etc.). After submission to the PDS, these data will be
    approved through the peer review process.

  Data Coverage and Quality
  =========================

    Gaps
    ----
      There are many gaps in the CAPS data stream and there are many
      different sources for these gaps.  Sources of gaps are as follows:
          a. telemetry outages
          b. data policing violations (CAPS data volume higher than
             allocated)
          c. incorrect spacecraft data management commanding
          d. telemetry commanding during Cruise
          e. instrument anomalies
          f. instrument modes which don't return all data products
          g. planned instrument power-off and/or sleep periods
          h. instrument off due to bus imbalance/short issues
      When there is no data for a time period, one of the above sources
      is the reason behind the gap.  There is no indicator to which of
      the sources is responsible for the gap in data coverage.

    Poor Data
    ---------
      Even in environments that are condusive to moment generation, other
      factors may influence the quality of the calculation.  For each record
      in the file, there is an associated quality flag that should be
      examined to determine the teams confidence in the quality of the
      calculation.

  Limitations
  ===========
      The main limitation for ION moments is that the data are only
      generated during periods where the environment is condusive to moment
      generation.