Voyager UVS DATASET.CAT
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PDS_VERSION_ID = PDS3
LABEL_REVISION_NOTE = "M.R. SHOWALTER, 2003-12-05"
RECORD_TYPE = STREAM
OBJECT = DATA_SET
DATA_SET_ID = "VG1/VG2-SR/UR/NR-UVS-2/4-OCC-V1.0"
OBJECT = DATA_SET_INFORMATION
DATA_SET_NAME =
"VG1/VG2 SR/UR/NR UVS EDITED/RESAMPLED RING OCCULTATION V1.0"
CITATION_DESC = "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."
ARCHIVE_STATUS = IN_PEER_REVIEW
DATA_SET_COLLECTION_MEMBER_FLG = Y
DATA_OBJECT_TYPE = SERIES
START_TIME = 1980-08-23T00:00:00
STOP_TIME = 1989-10-03T00:00:00
DATA_SET_RELEASE_DATE = 2003-12-31
PRODUCER_FULL_NAME = "MARK R. SHOWALTER"
DETAILED_CATALOG_FLAG = N
DATA_SET_TERSE_DESC = "
This data set contains stellar occultation data from the Voyager
Ultraviolet Spectrometer. It includes ring profiles from Saturn,
Uranus and Neptune at several levels of processing, plus geometry and
calibration files, software and documentation."
DATA_SET_DESC = "
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 Facility
(NAIF) Node at:
//pds.jpl.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 Ring-Moon Systems 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."
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."
END_OBJECT = DATA_SET_INFORMATION
OBJECT = DATA_SET_TARGET
TARGET_NAME = "S RINGS"
END_OBJECT = DATA_SET_TARGET
OBJECT = DATA_SET_TARGET
TARGET_NAME = "U RINGS"
END_OBJECT = DATA_SET_TARGET
OBJECT = DATA_SET_TARGET
TARGET_NAME = "N RINGS"
END_OBJECT = DATA_SET_TARGET
OBJECT = DATA_SET_HOST
INSTRUMENT_HOST_ID = VG2
INSTRUMENT_ID = UVS
END_OBJECT = DATA_SET_HOST
OBJECT = DATA_SET_REFERENCE_INFORMATION
REFERENCE_KEY_ID = "N/A"
END_OBJECT = DATA_SET_REFERENCE_INFORMATION
END_OBJECT = DATA_SET
END
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