Data Set Information
DATA_SET_NAME LICK1M SR CCD-CAM RESAMPLED RING OCCULTATION V1.0
DATA_SET_ID LICK1M-SR-CCDC-4-OCC-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : This data set contains stellar occultation data from the 1989 occultation of 28 Sagittarii (28Sgr) by Saturn obtained by the 1 meter Nickel reflector (LICK1M) at the Lick observatory . Data include occultation profiles for both ingress and egress which each cover a radial slice from the outer edge of Saturn's atmosphere to beyond the orbit of the F-ring. Ring profiles are archived as resampled normal optical depth profiles. Geometry solutions and noise models are also provided. Parameters : The raw data were obtained with a frame-transfer CCD. Only a subframe of each full CCD frame was recorded: after 2 x 2 on- chip pixel rebinning, each exposure consisted of a 54 x 90 pixel image with the long axis roughly parallel to Saturn's ring system. An RG-9 filter with a central wavelength of 0.9 microns and a full width at half-maximum of 0.25 microns spanned the 0.89 micron methane absorption band, substantially reducing the brightness of Saturn's disk. Three continuous sets of 1-s exposures were taken corresponding to ring ingress and atmosphere immersion, mid occultation, and atmosphere emersion and ring egress. Absolute timing was provided by synchronizing the CCD controller with a WWVB clock; dead time between images was only a few ms. Processing : Preliminary reduction of the images consisted of sky-frame subtraction, subpixel accuracy registration through rebinning, aperture photometry, correction for varying atmospheric transmission (see NICHOLSONETAL2000). The fully processed and resampled ring profiles have been generated as follows: (1) Observations of the 28 Sgr occultation made from several observatories were combined with Voyager PPS and RSS data sets to determine precisely the ring radial scale and the Saturn pole orientation (FRENCHETAL1993, HUBBARDETAL1993, NICHOLSONETAL2000). (2) Using the improved ring radial scale, the time-series of raw samples was converted to a uniformly-spaced series of radial samples. The spatial sampling interval used was 10 km, corresponding to Nyquist-sampled data based on the apparent star diameter of approximately 18 km. (3) Raw data DN levels were converted to normalized flux based on the viewing geometry, and subsequently to normal optical depth. Data : Derived profiles (DATA/LICK1M sub-directory) -------------------------------------------- The resampled data are presented in seven column ASCII tables. The columns are (1) radius(km), (2) normalized flux, (3) sigma flux, (4) normal optical depth(tau), (5) tau lower, (6) tau upper, (7) quality flag. The quality flag has five possible values. They are: 0:ok, 1:tau greater then tau_max, 2:non-photometric, 3:corrupted data, 4:missing data. For detailed discussion of the model used to determine noise and reasonable values for optical depth see MODEL.TXT in the DOCUMENTS sub-directory. In general, for corrupted or missing data, dummy values of 9.9990 are used in columns 3-6. Ancillary Data : Browse data (BROWSE/LICK1M sub-directory) ----------------------------------------- This subdirectory contains plots of radial profiles of stellar flux normal optical depth of the rings as derived from the observations of the 28 Sgr occultation by the rings of Saturn. Each plot is based on the corresponding profile data file in the corresponding subdirectory of the DATA directory. Geometry information (GEOMETRY/LICK1M sub-directory) ---------------------------------------------------- Supplemental geometry information is not available for the Lick observations 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. In some cases, B1950 coordinate values are also included. Media/Format : This data set is archived on compact disc (CDROM) media. Organization and formats are according to PDS and ISO 9660 level 2 standards. Most binary data files are in least-significant-byte first, which is the native format for PCs and Digital workstations. Users of Suns and other workstations may need to swap bytes in some data files before use. Note that the software tools provided on this volume swap the bytes automatically if this is necessary.
DATA_SET_RELEASE_DATE 2004-03-30T00:00:00.000Z
START_TIME 1989-07-03T04:00:00.000Z
STOP_TIME 1989-07-03T10:00:00.000Z
MISSION_NAME SATURN OCCULTATION OF 28 SAGITTARIUS 1989
MISSION_START_DATE 1989-07-03T12:00:00.000Z
MISSION_STOP_DATE 1989-07-03T12:00:00.000Z
TARGET_NAME SATURN
S RINGS
TARGET_TYPE PLANET
RING
INSTRUMENT_HOST_ID LICK1M
INSTRUMENT_NAME STOVER CCD SPECTROGRAPH CAMERA
INSTRUMENT_ID CCDC
INSTRUMENT_TYPE CAMERA
NODE_NAME Planetary Rings
ARCHIVE_STATUS ARCHIVED
CONFIDENCE_LEVEL_NOTE Confidence Level Overview : Overall the confidence level is high. Flawed data are clearly identified by non-zero values for the quality flag. The observations were taken at relatively high air mass (decreasing from 2.5 to 2.2 during ingress, and gradually increasing from 2.0 to 2.1 during egress). The data providers applied a correction for varying atmospheric transmission. Adopting an extinction coefficient of 0.04 mag/air mass, they scaled the lightcurves to their predicted levels for a constant air mass of 2.0. Finally, they determined the constant ring background and full stellar flux levels separately for ingress and egress from the immersion and emersion atmosphere lightcurves, and used these to scale the profiles to units of full stellar flux. The ingress lightcurve is the noisier of the two because it was observed at higher air mass, and is thus more susceptible to seeing noise and transparency variations. Nevertheless, the overall normalization is quite robust for both lightcurves, judging from the consistency between the full stellar intensity level determined from the atmosphere lightcurves and the free- space stellar signal outside of the rings. For the egress observations, the typical noise level is 0.025 per 1-s integration, with a corresponding maximum detectable optical depth, tau max, of 1.6. Peer Review : Peer review of this data set was completed in February 2005. The peer reviewers were Shawn Brooks (JPL), Richard G. French (Wellesley College), Colleen A. McGhee (Wellesley College), Cathy Olkin (South West Research Institute), and Leslie Young (South West Research Institute). The data set was also reviewed at the PDS Engineering Node by Steven L. Adams. Data Coverage and Quality : For the approximately last half of the egress observations, cloud cover significantly affected the observations. Ring features can still be detected, but the observing team judged that absolute flux values are not valid. These data are flagged as non- photometric in the resampled data files.
CITATION_DESCRIPTION French, R.G., P.D. Nicholson, M.K. Gordon, Radial Profiles of Saturn's Rings from the Lick 1 Meter Telescope Observations of the 1989 Occultation of 28 Sgr, LICK1M- SR-CCDC-4-OCC-V1.0, USA_NASA_PDS_EBROCC_0001, NASA Planetary Data System, 2003.
ABSTRACT_TEXT not applicable
PRODUCER_FULL_NAME MITCHELL K. GORDON
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