Data Set Overview : This data set contains stellar occultation data from the 1989 occultation of 28 Sagittarii (28Sgr) by Saturn obtained by the 1.0 meter telescope (ESO1) at the European Southern 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 data were obtained at 3.4 microns, using InSb nitrogen- cooled aperture photometers in the chopping mode. The chopping frequency was 8 Hz with a 68-arcsec E-W throw. The effective focal ratio was f/35, and 5-arcsec diaphragms were used to minimize background noise. Data were recorded digitally at 100 Hz.   Processing : No information is available concerning the preliminary reduction of the data.  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/ESO1M 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/ESO1M 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/ESO1M 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.

Confidence Level Overview : Overall the confidence level is good. Flawed data are clearly identified by non-zero values for the quality flag.   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 : Observing conditions were good throughout the occultation. The average seeing was 1.2 arcsec in the visible and 1.4 arcsec in the infrared. Atmospheric immersion occurred during the C Ring occultation, commingling ring features with the spikes in the atmosphere occultation light curve. Nonetheless, identifiable ring features could be measured throughout most of the ingress and egress occultations.  There is some evidence of timing problems with this data set. These observations should be treated as providing accurate relative measurements of the times of ring features, but not accurate absolute ring event times. For a more detailed discussion, see FRENCHETAL1993.