Data Set Overview
   =================
    This dataset contains images of the Saturn system taken at the
    NASA Infrared Telescope Facility (IRTF) using the NSFCam in early
    August 1995. This period preceeds the actual August plane crossing
    by 4 days. The Viewing geometry was such that the Earth and the
    Sun were on opposite sides of the ring plane, and the ring opening
    angle was less than 0.2 degrees.

    Every image showing Saturn, its rings or the region of the
    inner satellites has been included in this data set, regardless
    of the original intended purpose.

    The IRTF observing program whose results are included in this
    dataset is:

    Details on thse observations and the subsequent processing and 
    analysis can be found in:

    Bauer, J., J.J. Lissauer, and M. Simon, Edge-on observations of 
    Saturn's E and G Rings in the Near-IR, Icarus 125, 440-445, 
    1997.    
    
    Proposal: NAGW-4659
    Title:    Unknown
    PI:       Bauer, James (State University of New York, Stony Brook)


  Objectives
  ==========
    The primary objective for this set of observations was to obtain 
    detailed spectral information about the faint E Ring.

    The secondary objective was to obtain some photometric and 
    astrometric data for the following satellites of saturn: Janus, 
    Pandora, Prometheus, Epimetheus, and Enceladus.


  Observation summary and conditions
  ==================================  
    The Instrument used to study the Saturn Ring Plane Crossing 
    event was the NSFCam, the facility 256x256 InSb array camera, 
    with a pixel size of 0.31 arcsec. The Saturn system was viewed 
    through six filters. These filters are used to reduce the 
    planet's disk brightness. They are described briefly below:

     (1) the standard J band filter centered at 1.26 microns
     (2) A narrow filter within the H band centered at 1.62 microns
     (3) A narrow band filter in the K band centered at 2.21 microns
     (4) A standard L' filter centered at 3.78 microns
     (5) Two narrow band filters, Spencer 1.7 and Spencer 2.3
          centered at 1.73 and 2.28 microns respectively.

    Several thousand exposures were taken on the nights of August 
    6th, 7th, and 8th of 1995. There was also a series of calibation 
    runs using standard stars on the nights of May 21st, 22nd, and 
    25th. The calibration observations were made at airmass similar 
    to the faint ring and satilite exposures.

    The night on which the best faint ring data were obtained was
    photometric at about the 10% level. The seeing was roughly the
    same for all three nights. The image preparation and data
    reduction were done in IDL.


    Non-Linearity
    ==============
    The total counts are the sum of the CO-ADDs and non-destructive 
    reads(NDR) stacked on top of eachother. The number of CO-ADDs (CO_ADDS), 
    NDRs (NDR) and the number, or divisor that the image counts should be 
    divided by (DIVISOR) are keywords in the header, but the DIVISOR keyword 
    is the accurate one. The CAL files have the DIVISOR value divided out of 
    the count values, the RAW files do not. Linearity, or the point of 
    non-linearity depends on the detector voltage gain (keyword VDET). 
    Far beyond the linearity level, and the counts become negative in the 
    image. Prior to this, but still in the nonlinear regime, the image pixels 
    can take on a cross-hatched or canvas appearance. A few hundred counts 
    above nonlinearity results in a few percent nonlinearity in the counts. 
    At 1000 counts above and the non-linearity is severe.

        VDET  Start of Nonlinearity (approx & conservative)
        -3.4   2000-2500
        -3.2   4000
        -2.9   8000
        -2.7   10000 

    Hence the number of counts in the frame will be increased by a factor
    equal to the number of NDR. If more than [1] coadd has been requested
    then this entire process is repeated for the number of coadds, and the
    frame that is stored is the sum of the frames. Hence when reducing
    your data the counts in each frame need to be divided by the number of
    NDR and the number of coadds. This value is given in the FITS header
    as 'Divisor'. 
    
    At the time of writing a non-linear correction has not been determined
    for NSFCAM - however a correction will be determined in the near future.
    The array behaves in a similar manner to the CSHELL SBRC InSb array. The
    plots shown in the back of the CSHELL manual of counts versus 
    integration time, as a function of bias voltage, can be used as a guide 
    for the camera. These relationships imply the following conservative 
    upper limits to retain linearity in your data:

        TABLE 9.1: Maximum Counts for Data Linearity
        VDET           -3.4      -3.2     -2.9       -2.7
        bias mV       300       500      800       1000
        Counts should not exceed
        (excluding bad pixels)
               2000       4000   8000    10000


    Observations of photometric standards with a 300mV bias show that 
    counts around the 2500 level result in a 5% non-linear effect. 
    
    ( Some of the information above is taken from the NSFCam users 
    guide located in the DOCUMENT directory in this archive. )
    

  Parameters
  ==========  
    The PDS label for each file contains a broad variety of 
    additional parameters enabling the user to determine image 
    geometry and to convert pixel values to physically meaningful 
    quantities.


  Processing
  ==========
    The calibrated images have been processed using IRAF. This
    includes: analog bias correction, dark current correction, flat
    field correction, and sky correction. Spectra wavelengths were
    registered with a copper-argon reference source and compared to
    known absorption lines in the spectra.


  Data
  ====
    The data provided here are images in FITS format. For each data
    file, a detached PDS label is provided containing additional
    parameters.

    Most users will probably prefer to focus on the calibrated images
    or the processed data.

    Most of the calibration data may be found in subdirectories 
    under the /CALIB/ directory. However, ring observations were 
    made in a mode whre the images alternated by target and sky. 
    These associated sky images are in the separate subdirectories 
    under the /DATA/ directroy. Below the /CALIB/ and /DATA/ 
    directories, the data are furthur subdivided by date_target 
    directories, and finally processing level.


  Ancillary Data
  ==============
    Additional calibration files are provided to assist in the
    analysis and interpretation of the data.

    The appropriate subdirectories under the CALIBRATION 
    subdirectory contain bias, flat field, sky, and spectral 
    standard files as well as filter profiles for most of the 
    filters used in this data set.


  Coordinate System
  =================  
    All geometric quantities appearing in the labels are in J2000 
    coordinates. In this coordinate frame, the z-axis points 
    northward along the Earth's J2000 rotation axis and the x-axis 
    points toward the First Point of Aries.


  Media/Format
  ============  
    This data set is archived on electronic media. Organization and 
    formats are according to PDS and ISO 9660 level 2 standards.

Confidence Level Overview
  =========================  
    The NSFCam was calibrated using standard stas HD1160 and 
    HD161903 as well as the UKIRT faint standard stars fs27, fs28, 
    and fs32. These calibration runs were made at airmass similar to 
    faint ring and satelite exposures during the ring plane 
    crossing.
    
    The night on which the best faint ring data was obtained was 
    photometric at about the 10% level. The seing was roughly the
    same for all three nights.


  Review
  ======  
    This data set passed peer review on August 29, 2007. The peer 
    reviewers were James Bauer, Steve Larson, and Cathy Olkin. Ron 
    Joyner represented the PDS Engineering Node at JPL.


  Data Coverage and Quality
  =========================
    The deepest exposures targeted the region beyond the East and West
    ring ansae of the main rings. To reduce scattered light, Saturn's
    limb was placed just off the array's edge for these exposures. The
    best exposures were obtained on August 8th, when East ansae was
    clear of the saturnian satelites.


  Citing this dataset
  ===================
    The following is the recommended information to include in a
    journal citation of this dataset: Bauer, J., J.J. Lissauer, and
    M. Simon, IRTF Observations of the August 1995 Saturn Ring Plane
    Crossing, IRTF-S-NSFCAM-1/3-RPX-V1.0, USA_NASA_PDS_RPX_0201, NASA
    Planetary Data System, 2008.