Data Set Information
DATA_SET_NAME VG1/VG2 SR/UR/NR UVS EDITED/RESAMPLED RING OCCULTATION V1.0
DATA_SET_ID VG1/VG2-SR/UR/NR-UVS-2/4-OCC-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : This data set contains stellar occultation data obtained by the Voyager Ultraviolet Spectrometer (UVS). It includes ring occultation profiles from Saturn, Uranus and Neptune. It does not include other types of data obtained by the Voyager UVS. The specific ring occultation experiments carried out by UVS are: ----------------------------------------------------------- Planet Star Direction Vgr Comments ----------------------------------------------------------- Saturn iota Her egress 1 Inner C Ring only Saturn delta Sco ingress 2 Inner C Ring only Saturn delta Sco egress 2 Entire ring system Uranus sigma Sgr both 2 Delta, Lambda and Epsilon rings only Uranus beta Per both 2 All rings Neptune sigma Sgr ingress 2 All rings ----------------------------------------------------------- Ring profiles are archived in a variety of formats, from raw data to calibrated and resampled optical depth profiles. Processing software, geometry solutions and calibration models are also provided. Parameters : Raw data files contain a time series of spectra, where each spectrum consists of 126 wavelength samples. UVS counts are proportional to the number of photons received, with roughly 2.5 UVS counts per photon. Samples are time-tagged by Voyager's internal clock, the Flight Data System (FDS) count. Sampling intervals are 0.32 sec in occultation mode. Processing : Data are archived at a variety of levels of processing. The fully processed, resampled and calibrated ring profiles have been generated as follows: (1) Raw data files are edited to flag missing and invalid data and are padded as necessary to yield a continues, uniformly-spaced time series of data. (2) To improve signal-to-noise ratio, a selected range of wavelengths is summed to yield a single value. (3) A geometry model is used to match up each raw sample in the edited data file with the corresponding intercept point in the ring plane. The GEOMETRY directory contains these files; in some cases a geometry file comes in several versions to record the differing geometry solutions that various investigators have obtained. (4) A calibration model is used to determine the number of background photons and the number of stellar photons corresponding to a given sample. The CALIB directory contains these files. As with geometry, multiple calibration models are provided for many rings. (5) Using the geometry model, the time-series of raw samples is converted to a uniformly-spaced series of radial samples, in which each new radial sample is calculated via a weighted average of the relevant raw samples. Invalid and missing samples are zero-weighted at this step. (6) Using the weighting function described above and the known noise properties of the raw data, the uncertainty in each resampled value is calculated. (7) Resampled photon count values are converted to ring opacity tau using the calibration model, via the following formula: measured_counts : background_counts + stellar_counts*exp(-tau/mu) where mu is the cosine of the emission angle (listed in the labels of the geometry files). (8) By adding or subtracting the derived uncertainty from the measured count value and then solving the formula above for tau, the confidence interval on the ring opacity is derived. Data : A variety of data files are included on this volume. Source data (SORCDATA directory) -------------------------------- The (typically) binary data files as contributed to the Rings Node by several investigators. These files are provided for documentation purposes and are not otherwise supported. Raw data (RAWDATA directory) ---------------------------- These files contain essentially the same data as are found in the SORCDATA directory, but with time tags corrected. Edited data (EDITDATA directory) -------------------------------- Edited versions of the raw data, padded with empty records to represent continuous, uniformly-spaced time-series of UVS spectra and spectral sums. Invalid and missing data samples are flagged. These are the easiest binary files to use and are recommended for most purposes. Derived profiles (EASYDATA directory) ------------------------------------- Easy-to-use ASCII data files containing ring opacity and its uncertainty vs. radial location in a ring system. Files are included at a variety of radial resolutions: 0.2, 0.5, 1, 2, 5, 10, 20 and 50 km per sample. Because the rings of Uranus are narrow and inclined, there are separate profiles for each Uranian ring. Also provided are calibrated ring profiles that have not been radially resampled. Instead, they are subsampled at integer multiples of the original spacing. Ancillary Data : Many different types of ancillary data files are provided to document the PPS experiments and to describe the geometry and calibration during each occultation. Geometry models (GEOMETRY directory) ------------------------------------ ASCII data files, containing a description of the ring intercept geometry at times matching the data records in each corresponding edited data file. Because the rings of Uranus and Neptune are inclined, there are separate geometry files for each ring of these planets. Trajectory models (TRAJECT directory) -------------------------------------- ASCII data files, containing a position and velocity of Voyager relative to the center of the planet at times matching the data records in each corresponding edited data file. Calibration models (CALIB directory) ------------------------------------ ASCII data files, containing the modeled stellar and background photon count rates at times matching the data records in each corresponding edited data file. Noise models (NOISDATA directory) --------------------------------- Edited, binary data files in which the known rings of Uranus and Neptune have been removed. These are used for fitting some calibration models. Their formats are identical to the corresponding edited data files. Support images (IMAGES directory) --------------------------------- Voyager support images obtained before, during and after the ring occultations. Ephemeris files (SPICE directory) --------------------------------- Voyager ephemeris files for each of the planetary encounters, in SPICE format. For more information about SPICE data and toolkits, consult the PDS Navigation and Ancillary Information (NAIF) Node at: http://pds.nasa.gov/naif.html 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. Software : Included on this disk is the source code for several libraries of software tools designed to be used with this and other ring occultation data sets. Light Label Library (SOFTWARE/OAL directory) -------------------------------------------- A toolkit supported by the PDS Central Node for reading and writing PDS labels. Object Access Library (SOFTWARE/OAL directory) ---------------------------------------------- A toolkit supported by the PDS Central Node for reading and writing data objects described by PDS labels. Built atop the Light Label Library. Profile Library (SOFTWARE/PROFILE directory) -------------------------------------------- A toolkit supported by the PDS Rings Node for manipulating one-dimensional profiles of planetary rings. Built atop the Light Label Library and the Object Access Library. Also included are the software tools to generate calibrated ring profiles at arbitrary resolution. These are the tools used to populate the EASYDATA subdirectories. These tools make full use of the above libraries. Media/Format : This data set is archived on compact disc (CDROM) media. Organization and formats are according to PDS and ISO 9660 level 1 standards. Binary data files are provided in native formats for most platforms. Also, note that the software tools provided on this volume handle binary conversions on the fly if this is necessary.
DATA_SET_RELEASE_DATE 2003-12-31T00:00:00.000Z
START_TIME 1980-08-23T12:00:00.000Z
STOP_TIME 1989-10-03T12:00:00.000Z
MISSION_NAME VOYAGER
MISSION_START_DATE 1972-07-01T12:00:00.000Z
MISSION_STOP_DATE N/A (ongoing)
TARGET_NAME N RINGS
S RINGS
U RINGS
TARGET_TYPE RING
INSTRUMENT_HOST_ID VG2
INSTRUMENT_NAME ULTRAVIOLET SPECTROMETER
INSTRUMENT_ID UVS
INSTRUMENT_TYPE ULTRAVIOLET SPECTROMETER
NODE_NAME Planetary Rings
ARCHIVE_STATUS ARCHIVED
CONFIDENCE_LEVEL_NOTE Confidence Level Overview : Strong variations in overall photon count are correlated with instrument pointing changes, because the UVS field of view is narrow relative to Voyager's 'limit cycle' motion. As a result, sensitivity varies substantially within each single data set. The calibration models show these variation. Nevertheless, subtle features in the data that correlate with these sensitivity variations should be regarded with some skepticism. The data from the Uranus beta Per occultation were dominated by the charged particle background at Uranus. As a result, the rings are not detectable. Peer Review : Peer review of this data set is in progress. Data Coverage and Quality : The UVS experiments provided complete coverage of the ring systems of Saturn and Neptune. Only the outer part of the Uranian ring system is covered at reasonable sensitivity, including the Delta and Epsilon Rings. A few small, isolated gaps are present. In the edited data files, missing data samples have been indicated via a MISSING_CONSTANT flag. Unreliable samples have been replaced by an INVALID_CONSTANT flag. Unedited versions of the same data are also provided.
CITATION_DESCRIPTION Showalter, M.R., P.D. Nicholson, A.L. Broadfoot, W.T. Forrester, and J.B. Holberg, VG1/VG2 SR/UR/NR UVS EDITED/RESAMPLED RING OCCULTATION V1.0, VG_2802, NASA Planetary Data System, 2004.
ABSTRACT_TEXT not applicable
PRODUCER_FULL_NAME MARK R. SHOWALTER
SEARCH/ACCESS DATA
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