Data set Version 2.0
      ====================
      The Science RIDs from the October 2018 review have been applied
      to this ROSINA dataset. The ROSINA team also found corrupted
      files in the RTOF, DFMS, and COPS science data V1.0 of this
      dataset, these corrupted files have been removed in the V2.0.
      The list of these removed files can be found in the
      REMOVED_L2_V1_TO_V2.ASC file. Some of the DFMS PDS files were
      missing in the L2 V1.0 and were added them into the V2.0.
      The COPS science HK order also changed without modifying the
      structure: the COPS HK table composed by the 5 last standard
      COPS HK blocks are now in time order, this change is reflected
      in the latest version of the ROSINA EAICD document. As a result,
      V2.0 of this CODMAC L2 dataset has been created.

      Data set Overview
      =================
      Rosetta was at distances between 320 and 46 km from the comet
      during this time.
      ROSINA was permanently analyzing the coma of the comet with all
      three sensors, except during wheel offloadings when the mass
      spectrometers DFMS and RTOF were in standby and during orbit
      control manoeuvers, when all sensors were off. Explanations
      on the data generation of the ROSINA sensors can be found in
      the OPERATION_LOGBOOK.ASC

      Parameters
      ==========
      DFMS and RTOF data contain neutral gas data as well as ion data.
      The data are raw, uncalibrated data. COPS data contains nude
      gauge pressure values of the combined spacecraft and cometary
      signal.

      Calibration
      ===========
      COPS data are calibrated. However, the calibration factor has
      been determined for Nitrogen gas, and may not be appropriate for
      the the coma composition. For this the data from RTOF or DFMS
      have to be taken into account.

      Note on the DFMS and RTOF data:
      The user of our level 2 data has to make the conversion from
      pixel to mass and from ADC counts to ion current himself. In
      this way he will be aware that the precision is limited and
      depends on many parameters and he will use the data accordingly.
      The procedure required to calibrate the DFMS is described in our
      User manual, Annex D1 (DOCUMENT directory). ROSINA team are
      developed the necessary algorithms, putting emphasis on the
      quality control for the algorithm. They are defining quality
      flags for the data which will then tell the user how well the
      mass scale and the intensity scale have been defined.
      For calibrated level 3 data with calibrated mass scale and
      intensity we refer the user to the level 3 data.

      Processing
      ==========
      The DPU measures the ion current. To calculate the pressure,
      the DPU use the following formula:
      For the nude gauge:

      p(mbar)NG = (Ion_current_fil(A) - Ion_offset_fil(A)) /
            (Immission_current_fil(A) - Immission_offset_fil(a)) * S

      For the ram gauge:

      p(mbar)RG = (Ion_current_mic(A) - Ion_offset_mic(A)) /
            (Immission_current_mic(A) - Immission_offset_mic(a)) * S


      The Ion offset value is measured in background mode, that is
      after switching on and then every 24h with the filament and the
      microtips, respectively off. S is the calibration factor, it is
      about 30 for the nude gauge and 5 for the ram gauge.
      This factor depends of the temperature and the ambient gas.

      Flux formula for the Ram gauge:

      phi_out = 0.25 * SQRT((8*kB+T_RG) / (pi * mass)) *
                   (p_RG / (T_RG*kB))

      phi_out = gas flux [1/m2*s]
      kB = Boltzmann-constant = 1.38e-23 [J/K]
      T_RG = ram gauge temp. [K]
      mass = 18 amu = 2.9889e-26 [ Kg] (H2o is the default mass)
      p_RG = ram pressure [Pa] = 100*[p(mbar)RG]

      The pressure values given directly in the COPS housekeeping are
      pressures for N2 at 20DegC. In order to derive the density this
      pressure value has therefore to be converted to density as
      follows:
      n (m-3) = p /(kT) with p in Pa; T=293K, k=1.380*10e-23 J/K
      e.g. if p=1*10e-10 mbar n=2.4*10e12 m-3 = 2.4*10e6 cm3

      In order to get the real density, the relative contribution of
      the different species in the coma has to be known, as ionization
      cross sections are different for each gas. For more details see
      the ROSINA user manual.

      Software
      ========
      No software is provided.

      Media/Format
      ============
      The standard distribution format for the data is an electronic
      volume.

      Coordinate System
      =================
      The geometry items SC_SUN_POSITION_VECTOR,
      SC_TARGET_POSITION_VECTOR and SC_TARGET_VELOCITY_VECTOR provided
      in the label of the data product are relative to the Earth Mean
      Equator and Equinox reference frame of J2000.
      SUB_SPACECRAFT_LATITUDE, SUB_SPACECRAFT_LONGITUDE are given in
      the Cheops reference frame.
      The SPACECRAFT_ALTITUDE gives the distance to the spacecraft
      from the target center of mass. These parameters are computed at
      time t=START_TIME.
      Distances are given in km, angles in degrees.

      Cheops Reference Frame
      ======================
      Scholten, F., Preusker, F., Jorda, L, and Hviid, S.,
      Reference Frames and Mapping Schemes of Comet 67P/C-G,
      RO-C-MULTI-5-67P-SHAPE-V1.0:CHEOPS_REF_FRAME_V1,
      NASA Planetary Data System and ESA Planetary Science Archive,
      2015.

Confidence Level Overview
      =========================
      All data have been validated by the ROSINA team and found as
      expected. Any exceptions are noted by the DATA_QUALITY field in
      the label files.