Data Set Overview
    =================
      This data set contains science, calibration and checkout images
      acquired by the OSIRIS Narrow Angle Camera system on the Rosetta
      mission.

      The images were acquired during the escort mission phase
      covering the period from 2015-03-10 to 2015-04-08.


      The images are CODMAC level 2.


    The ESC2 mission phase covers the escort of comet 67P/ Churyumov-
    Gerasimenko after the landing of Philae




 Essential Reading
 -----------------

 The following documents, located on the dataset DOCUMENT folder, are
 essential for the understanding and interpretation of this data set:

 OSIRIS_SSR.PDF:         Gives an overview of the science goals
                         of the OSIRIS instrument and an overview of
                                       the instrument hardware.

 OSIRIS_SIS.PDF:         Describes the OSIRIS PDS header

 Related Data Sets
 -----------------


      The following PDS data sets are related:

            RO-C-OSINAC-3-ESC2-67PCHURYUMOV-M14-V1.0
            RO-C-OSIWAC-2-ESC2-67PCHURYUMOV-M14-V1.0
            RO-C-OSIWAC-3-ESC2-67PCHURYUMOV-M14-V1.0


  Processing
  ==========

        The PDS images in this data set were generated using the
      OSIRIS telemetry processing facility at the Max Planck
      Institute for Solarsystem Research from the raw telemetry
      stream sent down from the rosetta spacecraft. The decoded
      telemetry stream was initially saved as Level 1 PDS images
      (raw telemetry header and raw image data). These raw Level 1
      image files were then passed through a level 1 to level 2
      processing pipeline. This pipeline converts the raw telemetry
      header into calibrated physical values and appends additional
      information collected from external data sources (SPICE,
      sequence library ...)

        Given that the calibration database is considered a single
      product even if it can be used separately to calibrate images
      from the NAC and the WAC, it is delivered in its entirety on
      the NAC and WAC datasets.

  Data
  ====

    CCD Images
    ----------

      The OSIRIS images are stored as PDS images (meaning data files
      with embedded label where the image data is stored using an
      'IMAGE' PDS object. The raw image data is stored using a 16 bit
      unsigned integer low endian format.

      The pixel value 0 is used to indicate missing data (lost packets).


    Compression
    -----------

      The OSIRIS flight software has the capability to compress the
      image data before transmission to ground using a number of
      compression algorithms and filtering schemes.

      OSIRIS implements a data segmentation scheme to decrease
      sensitivity to data loss during transmission. Each image is
      separated into blocks with a maximum size of 512x512 pixels.
      Each of these blocks are processed and compressed individually.

      All information about compression and post-processing is located
      in the SR_COMPRESSION group in the OSIRIS image headers. Each
      member of this group is a vector containg a data entry for each
      image segment used to generate the final image. The pixel
      coordinates of the segmentation boundaries can be found using
      the SEGMENT_[X,Y,W,H] fields.
      The name of the algorithm used to encode the image data is located
      in the ENCODING field. The following encoding algorithms are supported:

                NONE         - No Compression
                SPIHT_D24     - Early implementation of the SPIHT algorithm
                               that divided all data values by 24 before
                               encoding
                SPIHT_LIFT   - SPIHT compression with LIFT filtering
                SPIHT_TAP    - SPIHT compression with TAP filtering
                SQRT_16to8   - Squarerooting followied by 16 to 8 bit
                               reduction
                PACK9BIT     - 16 to 9 bit truncation

      The effective compression ratio achieved by the encoder is
      stored in the COMPRESSION_RATIO member.

      If the encoding step was performed without information loss
      then the LOSSLESS_FLAG member is TRUE else FALSE. Please note
      that LOSSLESS_FLAG only refers to the encoding step.
      LOSSLESS_FLAG can be TRUE even is a lossy filtering step has
      been performed.

      OSIRIS can also perform a pixel averaging step. The pixel
      averaging box size can be found in the PIXEL_AVERAGING_WIDTH
      and PIXEL_AVERAGING_HEIGHT members.

      To increase the performance of the SPIHT compressor OSIRIS
      implements a number of optional pre encoding filtering steps.
      The following filtering are possible:

           1. A Gauss 5x5 convolution smooth filter
           2. A Sqrt filtering step performing the transformation
                   I_Out = sqrt(I * gain)

      The type of gauss smooth filter used can be found in
      SMOOTH_FILTER_ID with the values
                'NONE'
                'CONVOL_KERNEL_1' (0.5 FWHM)
                'CONVOL_KERNEL_2' (0.8 FWHM)
                'CONVOL_KERNEL_3' (1.0 FWHM)

      If the sqrt filter has been used the SQRT_FILTER_FLAG is set to
      TRUE and the used gain value is stored in the SQRT_FILTER_GAIN
      field.


    Target Name and Description
    ---------------------------

      The TARGET_NAME and TARGET_TYPE keywords in the data labels are
      automatically set by the processing software using the following
      hierarchal rules:

      1. The closest solar system object within 1 deg of the camera
         boresight (using a selected database of allowed targets).
         All solar system objects are given using a SPICE compatible
         object name.

      2. Any deep sky within 1 deg of the camera boresight (using
         a selected database of allowed targets).

      3. A number of special images which are acquired with the
         camera front door closed are named:

         Name         Type         Description
         ---------------------------------------------------
         CHECKOUT     N/A          Shutter Test Images
         CALIBRATION  CALIBRATION  Internal reference flatfield
         DARK         CALIBRATION  Dark/Bias current measurement

      4. TARGET_NAME = UNK   if no object was found matching the
         above criteria.


    Displaying the OSIRIS images
    ----------------------------

      The OSIRIS images are stored using the following format

               -----------------
               | header        |
               -----------------
               |pixel (0,0)    |
               |               |
               |               |
               |               |
               |               |
               |     pixel(w,h)|
               -----------------

      this structure means that the image (as is typical for PDS
      images) needs to be vertically flipped to be correctly
      displayed on a typical computer screen.

      On top of this the images from the narrow angle camera requires
      a horizontal flip to be shown with in the same geometry as the
      wide angle camera images.

      To summarize:

          OSINAC images:    flip horizontally + flip vertically
          OSIWAC images:    flip vertically

     Using these transformations the x-image axis is roughly aligned
     with the spacecraft y axis and the y-image axis is roughly
     aligned with the spacecraft x-axis.

  File Naming Convention
  ----------------------

      The OSIRIS image files use the following filenaming convention:

      CYYYYMMDDTHHMMSSUUUFFLIFAB.IMG

      where:
             C is either N  NAC (narrow angle camera)
                         W  NAC (wide angle camera)
             YYYY is the year of acquisition
             MM   is the month of acquisition
             DD   is the day of acquisition
             T    is the letter T
             HH   is the hour of acquisition
             MM   is the minute of acquisition
             SS   is the second of acquisition
             UUU  is the milli-second of acquisition
             FF   is the image file type:
                  the following filetypes are possible:
                        ID   Image Data  (Normal images)
                        TH   Thumbnail version of the image
                             (Highly compression version transmitted
                             immidiately)
                        PA   Amplifier A pre pixels  (cal data)
                        PB   Amplifier B pre pixels  (cal data)
                        OL   Overclocked lines       (cal data)
             L    is the processing level of the image
             I    is the instance id if the image
                  (multiple transmissions of an image will be
                   reflected in this number incrementing)
             F    is the letter F
             A    is the position of the filter wheel #1
             B    is the position of the filter wheel #2

             .IMG is the file extension

      Example:
             W20040923T071606570ID12F12.img

             Is a WAC image acquired at 2004-09-23 at 07:16:06.657 UTC
             The file contains CCD image data (image type ID) with raw
             image data (level 1) and the image represents the 2
             transmission of the image data. The image was acquired
             using the filter combination (1,2) = Hole+Red for
             the WAC.

      Note! The filename contains an approximate time of acquisition.
      This time value is only used to uniquely identify the image and
      should not be used for any calculation needing high precision.
      The time value in the filename has not been corrected for onboard
      clock drift and leap seconds. The best possible knowledge about
      the time of acquisition can be found in the header label
      START_TIME


  Parameters
  ==========

    Data Units
    ----------
      The images in this dataset contains values in raw Data Number (DN)
      (uncalibrated)


    Time-Related Keywords
    ---------------------
      All time-related keywords in the data labels are based on the
      clock inside the OSIRIS processing unit. This time is
      periodically synchronized with the Rosetta spacecraft clock.
      The conversion into real time (UTC) has been calculated using the
      official clock drift kernels maintained by the spacecraft
      operations center and leap second list maintained by the IERS.



  Ancillary Data
  ==============
    Geometric parameters included in the data labels were computed
    using the N64 release of the SPICE toolkit and the most up to
    date versions of the SPICE kernels available at the time of
    processing. The filenames of the SPICE kernels used for the
    calculations can be found in the SPICE_FILE_NAME field.

    For high presition work the header geometry information should be
    ignored in favour of direct calculation using the most up to date
    kernels.


  Coordinate System
  =================
    OSIRIS uses the Earth Mean Equator and Vernal Equinox of J2000
    (EME J2000) as reference inertial coordinate system.

    Geometric parameters provided in the data labels were computed at
    the epoch specified by START_TIME, except for the
    target-to-sun parameters, which were calculated for the time when the
    light left the sun .

    The OSIRIS label contains two groups defining usefull coordinate
    system transformation:

        1. SC_COORDINATE_SYSTEM
            Contains the offset and rotation needed to transform from
            EME J2000 to the Rosetta spacecraft coordinate system
            (Commong for all Rosetta payload elements)

        2. CAMERA_COORDINATE_SYSTEM
            Contains the offset and rotation needed to transform from
            the Rosetta spacecraft coordinate system to the camera frame
            coordinate system of the NAC camera.

Confidence Level Overview
  =========================

    The OSIRIS cameras are intended to deliver the highest resolution
    images ever acquired of a cometary nucleus (~4 cm per pixel)
    with the highest possible spectro photometric quality possible
    (NAC).

    The OSIRIS cameras are intended to deliver high quality line
    emission maps of the inner coma (WAC)

  Review
  ======

    The OSIRIS dataset will be reviewed first internally by the
    Rosetta project followed by a formal review by the PSA before
    release to the public.

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

  The OSIRIS EDR data records in the CODMAC level 2 data sets does not
  contain any estimate of the data quality. Quality information is
  embedded (on a per pixel level) in the calibrated CODMAC level 3
  data sets.

  The header field DATA_QUALITY_ID exists for legacy reasons but
  does not contain any usefull information.