Data Set Information
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| DATA_SET_NAME |
MCD27M SR INSB-IR-ARRY RESAMPLED RING OCCULTATION V1.0
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| DATA_SET_ID |
MCD27M-SR-IIRAR-4-OCC-V1.0
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| NSSDC_DATA_SET_ID |
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| DATA_SET_TERSE_DESCRIPTION |
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| 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 2.7 meter telescope (MCD27M) at the MacDonald 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 nearly 40,000 individual frames taken with a four channel visual aperture photometer using a 58 x 62 pixel InSb detector array using a 2.1 micron circular variable filter with a spectral resolution of 0.02. The data were recorded at a time resolution of 0.2 sec per frame. Both ingress and egress ring occultations were observed. Processing : Preliminary reduction of the images consisted of sky-frame subtraction, 0.1 pixel accuracy registration through rebinning, aperture photometry with corrections for nonlinear detector response and corrections for varying atmospheric transmission (NICHOLSONETAL1995, 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/MCD27M 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/MCD27M 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/MCD27M 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.
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| DATA_SET_RELEASE_DATE |
2004-03-30T00:00:00.000Z
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| START_TIME |
1989-07-03T04:00:00.000Z
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| STOP_TIME |
1989-07-03T10:00:00.000Z
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| MISSION_NAME |
SATURN OCCULTATION OF 28 SAGITTARIUS 1989
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| MISSION_START_DATE |
1989-07-03T12:00:00.000Z
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| MISSION_STOP_DATE |
1989-07-03T12:00:00.000Z
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| TARGET_NAME |
SATURN
S RINGS
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| TARGET_TYPE |
PLANET
RING
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| INSTRUMENT_HOST_ID |
MCD27M
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| INSTRUMENT_NAME |
INSB INFRARED ARRAY
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| INSTRUMENT_ID |
IIRAR
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| INSTRUMENT_TYPE |
CAMERA
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| NODE_NAME |
Planetary Rings
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| ARCHIVE_STATUS |
ARCHIVED
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| 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 normalized lightcurve arise from several sources. For a 3'' aperture radius, the array read noise is ~0.0026. Photon noise in the stellar signal is negligible by comparison. In practice, the dominant noise source near full stellar intensity (low optical depth) is seeing noise, which was measured to be 0.02 per 0.2-s integration. At low stellar intensity (high optical depth), the dominant source of error is uncertainty in the level of background ring flux present in the aperture, which was found to be 0.005. Other sources of error include vignetting in the optics and variable atmospheric extinction, which would introduce slow variations in the total signal. The data providers have attempted to correct these to better than 1% of the full stellar intensity. Photometry experiments show that systematic uncertainties in the B Ring are about 0.006, which sets a limit on the maximum detectable optical depth, tau max of 2.2. 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.
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| CITATION_DESCRIPTION |
French, R.G., P.D. Nicholson, M.K. Gordon, Radial Profiles of Saturn's Rings from the MacDonald 2.7 Meter Telescope Observations of the 1989 Occultation of 28 Sgr, MCD27M-SR-IIRAR-4-OCC-V1.0, USA_NASA_PDS_EBROCC_0001, NASA Planetary Data System, 2003.
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| ABSTRACT_TEXT |
not applicable
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| PRODUCER_FULL_NAME |
MITCHELL K. GORDON
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| SEARCH/ACCESS DATA |
Rings Node Interface
Rings Online Archives
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