Data Set Overview
  =================
    This data set contains digitized plots of the density of the
    lunar atmosphere as measured by the Apollo 14 Cold Cathode Ion
    Gage from 09 February 1971 through 31 December 1973.


  Data
  ====
    These data are digitized as part of the Lunar Data Project from
    experimenter-generated, 35-mm microfilm reels containing plots of
    lunar atmosphere density measurements and instrument temperature as
    a function of time.  Each frame consists of two plots with a common
    abscissa. The abscissa gives the time of the measurement in the form
    DDD/HH/MM where DDD is day of year, HH is hour, and MM is minute.
    All times are Greenwich Mean Time (GMT).  The lower plot gives
    measurements of the equivalent density for a nitrogen lunar
    atmosphere in particles per cubic centimeter on a logarithmic scale
    that ranges from 10 E4 to 10 E10 [10 E4 = 10 x (10 to the 4th power)
    = 100 000.]  The upper plot gives the instrument temperature on a
    linear scale from 0 to 400 Kelvin.  Most frames hold 15 hours of
    data.  Note that the ordinate range and scale are identical for all
    plots, the time scale on the abscissa is the same for most plots
    (some plots use an expanded scale) but the actual time range is
    different on each plot.  The data are not complete, the instrument
    was turned off on 5 January 1975, the later data were never received
    at the NSSDC.

    In the normal operational mode the basic cycle repeated five
    measurements (separated by 2.4 s), three measurements (separated by
    40 s), and 16 seconds of calibration and auto-zeroing every 2.5 min.
    Each of the measurements is represented by one point on the graph.
    In a ground commanded special mode, one measurement was obtained
    every 2.4 s, with no other measurements being performed.  There is
    no note on the plots indicating which mode the instrument is in.

    The actual raw signal returned by the instrument was the current
    measured by the sensors.  The sensors were calibrated in pre-flight
    tests using a pure nitrogen (N2) atmosphere.  The values shown on
    the plots have been converted from the sensor-measured current
    reading to the equivalent nitrogen-2 atmosphere density using the
    calibration curves of the appropriate gage and temperature sensor.
    The results are expressed in terms of the nitrogen-2 concentration
    which would produce the observed current after correcting for
    temperature.  The response of the instrument depends to a rather
    modest degree on the composition of the gas, which is not known,
    but it is assumed the true value will vary from this nitrogen-2
    concentration by a factor smaller than 2.

    The instrument underwent high-temperature arcing during the
    daytime, often indicated by data dropouts or switching between
    data modes.  Daytime data was also dominated by outgassing,
    particularly for the first few lunar days. The CCIG was turned off
    for periods during the lunar day early in its operational history
    because of this.  Sunrise and sunset effects were observed, and
    bursts were seen at night, particularly at pre-dawn times, which
    are believed to be real argon-40 events.  The difficulties
    encountered in setting up the CCIG instrument on Apollo 14 (see
    instrument catalog file in this archive) did not affect the results.

    The NSSDC digitized the original 35-mm microfilm reels of
    experiment-generated plots, data set PSPA-00104, as part of the
    Lunar Data Restoration project.  See Johnson, et. al (1972A)
    [JOHNSONETAL1972A], Johnson, et. al (1972B) [JOHNSONETAL1972B],
    Hodges, et. al (1974) [HODGESETAL1974], and the Apollo 14 Preliminary
    Science Report [APOLLO14A1971] for more information about the atmospheric
    density data from Apollo 14.  The Apollo 17 Lunar Atmosphere
    Composition Experiment (LACE) and the Apollo 15 and 16 Lunar Orbital
    Mass Spectrometers (LOMS) also returned data complementary to the
    CCIG instrument.  For more information about these experiments, see
    Hoffman, et. al (1973) [HOFFMANETAL1973] and Hodges, et. al (1972)
    [HODGESETAL1972].


  Scanning Procedure
  ==================
    The media chosen for storage of the original data was 35-mm silver
    microfilm. This microfilm was archived at NSSDC and was scanned to
    produce this digital data set.  The actual size of a frame on the
    microfilm is 19 x 29 mm.  The microfilm was mounted on an E-Image Data
    Scan Pro 300, previewed to allow settings for optimal scanning, and
    scanned at a resolution of 400 dpi (dots per inch) into tiff format
    using Photoshop CS2.  The original images were black and white
    negatives, the images were scanned as positives. Each scan captured
    one frame.  The machine is manually refocused every 3 to 5 scans.  A
    resolution of 400 dpi was chosen as the optimal tradeoff between
    clarity of the plots and scanning time required.  Plots scanned at 600
    dpi did not show noticeable improvement while requiring roughly twice
    the scan time.  Plots scanned at 300 dpi were not as clear as the plots
    scanned at 400 dpi.  No enhancement was performed on the image after
    scanning.  At a later date the data user may choose to enhance the
    image or can request the original microfilm using the ID to identify
    the requisite frames.

    Each frame was checked as part of the quality assurance (QA) process,
    frames that were unclear, corrupted, or missing were rescanned.  The
    scanning resulted in banding in many of the images, with bands of
    lighter and darker background color on the plots.  These bands are not
    on the original plots and are an artifact of the scanning process. (The
    location of the bands changes with each scan.)  The banding appears to
    have no effect on the readability of the data and is checked in real
    time as the frames are scanned and then the scans are compared to the
    originals as part of the QA process for any effect on the readability
    of the data.  The original microfilm reel has many splices where the
    frames are joined together.  These do not affect the data but the
    locations of the splices have been noted in the index and the label.
    Occasional short overlaps in the time span have also been found on the
    microfilm.  It is assumed that during the original creation of the
    microfilm or of the computer printout some of the frames were redone.
    These instances are noted in the index and the comments in the
    individual label file.

    The frame ID's are in the form AnnA_CCIG_yy_mmmmmmm_fff.tif where Ann
    is for the Apollo mission (that is, A14), the second A is for the ALSEP
    experiment CCIG is Cold Cathode Ion Gage, yy is the year of the data
    (such as, 71 for 1971), mmmmmmm is the microfilm reel ID, and fff is
    the frame number on that reel.  Scans are numbered by position on the
    microfilm to allow recovery of original analog data if necessary.


    This data set description was provided by the NSSDC.

Confidence Level Overview
  =========================
    The files were scanned directly from microfilm.  The original scans
    were done with the optimal focus and contrast, but no attempts were
    made to enhance the digital images.  Some images are difficult to read
    and may benefit from further enhancement by the user.


  Review
  ======
    This data set was peer-reviewed in December 2007 and was accepted for
    the PDS archive pending the resolution of liens (completed in June
    2008).