Data Set Information
DATA_SET_NAME PAL200 SR CASS-IR-CAM RESAMPLED RING OCCULTATION V1.0
DATA_SET_ID PAL200-SR-CIRC-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 Hale 5 meter (200 inch) telescope (PAL200) at the Mt. Palomar 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 consists of more than 64,000 individual frames taken with the Cassegrain IR camera using a 58 x 62 pixel InSb detector array with a circular variable filter (CVF). The units are DN/pixel. Each frame was recorded with an integration time of 0.15 sec. Both ingress and egress ring occultations were observed, but with 1.5 to 3.5 minute data gaps every 20 minutes associated with opening new disk files. Processing : Detailed descriptions of the data processing can be found in NICHOLSONETAL2000 and are summarized here. Preliminary reduction of the images consisted of sky-frame subtraction, flat-fielding, and simple aperture photometry on the flattened images. The original observations were combined to provide a time sequence of signal intensities. The raw data are sampled every 0.15 sec which corresponds to approximately every 3 km in the ring plane at Saturn. However, the raw data sampling is non- uniform in radius. The apparent diameter of the star was approximately 18 km, so the raw data are significantly over sampled. 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/PAL200 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. Saturn?s air mass varied from 2.15 at the start of observations, through a minimum of 1.77 at 7:48 UT, to 2.12 at the end. Sky conditions were excellent during the ingress period, but thin clouds affected the ring egress, especially the data for the A Ring. Throughout the period of ring occultations the telescope pointing was controlled by an autoguider set on a nearby star, so that 28 Sgr remained at an almost fixed location on the detector array while Saturn drifted slowly across the field. Absolute timing, tied to WWVB radio signals, was provided by periodic offsets applied to the telescope?s chopping secondary mirror. Further details on the timing calibration are provided in FRENCHETAL1993. Ancillary Data : Browse data (BROWSE/PAL200 sub-directory) ---------------------------------------- This subdirectory contains two types of plot for each observation run. 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. Plots of ancillary geometry information. Each plot is based on the corresponding profile data file in the corresponding subdirectory of the GEOMETRY directory. Geometry information (GEOMETRY/PAL200 sub-directory) ---------------------------------------------------- The geometry information is provided in separate files for ingress and egress. Data are arranged in four columns: a) Equatorial Radius (Km), b) Observatory received time (UTC), c) Ring Plane inertial longitude of the intercept point (deg), d) delta time (s). The latter is a correction factor used when determining the line-of-sight distance between the ring intercept point and the observer. The data are presented with uniformly varying radius (1000 km increments) between 73,000 km and 142,000 km. The data are arranged in the order of increasing radius regardless of whether the observation is ingress or egress. Geometry data were obtained using a polynomial fit. The polynomial coefficients can be found in DOCUMENTS/POLY_CO.TXT 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 PAL200
INSTRUMENT_NAME CASSEGRAIN IR CAMERA
INSTRUMENT_ID CIRC
INSTRUMENT_TYPE INFRARED IMAGING DEVICE
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. Photometric uncertainties in the raw ingress lightcurve are due to background noise (125 DN), shot noise in the stellar signal (36 DN unocculted), and array read noise (89 DN), for a total of sigma(F) of 158 DN. As the average unocculted stellar flux is 114,000 DN, this implies a formal 1 sigma measurement error at low optical depths of ~ 0.0006. In reality, the rms noise in the unocculted stellar signal due to seeing fluctuations is 1100?1200 DN, leading to a more realistic 1 sigma random measurement uncertainty of ~ 0.004. See NICHOLSONETAL2000 for the complete analysis. The flux normalization may also introduce systematic errors of as much as 4%, based on comparisons of different polynomial fits and observed slow flux variations prior to ingress, at least in regions far from the inner or outer edge of the ring system. This may lead to low-frequency errors in the optical depths of up to 0.02, independent of optical depth. 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, and M.K. Gordon Radial Profiles of Saturn's Rings from the Palomar 200 Inch Telescope Observations of the 1989 Occultation of 28 Sgr, PAL200-SR-CIRC-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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