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.