Data Set Information
|
DATA_SET_NAME |
CASSINI ORBITER SATURN ISSNA/ISSWA 5
MIDR VERSION 1.0
|
DATA_SET_ID |
CO-S-ISSNA/ISSWA-5-MIDR-V1.0
|
NSSDC_DATA_SET_ID |
|
DATA_SET_TERSE_DESCRIPTION |
Cassini Imaging Science Subsystem
Saturn Mosaicked Image Data Record
|
DATA_SET_DESCRIPTION |
Data Set Overview
=================
The Cassini ISS Cartographic Map archive dataset consists of
cartographic map sheets of Saturn's icy satellites Dione, Enceladus,
Iapetus, Mimas, Phoebe, Rhea, and Tethys. Additionally, the archive
volumes contains a global mosaic image, the processed tile images
used to create the cartographic map sheets, PDS label files, related
Cassini and ISS instrument documentation, index files of the maps
and images for use in data management systems, and other helpful and
required PDS files.
More information on the details of this volume can be found in the
document directory and the aareadme.txt file at the root level of
this volume.
Processing
==========
The cartographic maps were created from images taken by Cassini with
a very small number of images from Voyager-1 and Voyager-2 used to
fill in any gaps. Images taken from all three missions are
available online from the Planetary Data System (PDS) Imaging Node
[http://pdsimaging.jpl.nasa.gov].
Though the Cassini-ISS camera takes images using many different
filters, the only images used were taken with the filters CL1, CL2
or GRN, as these images show similar contrast.
Processing begins with the conversion of images from the PDS format
to the VICAR (Video Image Communication and Retrieval) format, then
followed by the radiometric and geometric calibrations using standard
VICAR programs [available from the website
http://rushmore.jpl.nasa.gov/vicar.html].
Next is conversion of the images to digital maps, which requires
precise orbit and pointing data for each image. For the Cassini
mission, spacecraft position and camera pointing data are available
in the form of SPICE kernels [http://naif.jpl.nasa.gov]. While the
orbit information is sufficiently accurate to be used directly for
mapping purposes, the pointing information must be corrected using
limb fits. High resolution images not containing the limb were
registered to limb images to improve the pointing. For the Cassini
maps, newly derived tri-axial ellipsoid models were used to
calculate the surface intersection points.
Digital maps are prepared in simple cylindrical projection, a
special case of equirectangular projection. The mapping cylinder is
tangent to the equator of the sphere, the longitude range is 0 to
360 W and latitude range -90 to 90. The prime meridian is in the
center of the map. For Cassini images, a photometric correction
using the Henyey-Greenstein function was applied to the image data
before mosaicking.
The inner Saturnian satellites are best described by tri-axial
ellipsoids as recommended in the report of the International
Astronomical Union (IAU).
However, to facilitate comparison and interpretation of the maps,
ellipsoids were only used for the calculation of the ray intersection
points, while the map projection was done onto a sphere with the mean
IAU radius.
The final step of the image processing is the combination of all map
projected images to a homogeneous mosaic. Special care must be taken
to handle the different ground resolutions within overlapping
regions and the variable illumination conditions in the different
images in order to minimize the loss of high-resolution image
information and contrast.
Data
====
Map Sheet PDF Files
-------------------
The full cartographic mapping product for a particular target body
consists of one or more cartographic map sheets. A map sheet
will contain one or more images of different projections of the
body. Also included on the map sheet is text information describing
the index of original images used to make the map, image processing
used, a summary of the map projections, references, and contact
information.
These map sheets are stored as PDF (Portable Document Format)
files. More information about PDF can be found in the 'Software'
section below.
Tile Image VICAR Files
----------------------
All tile images are in VICAR image format. More information about
this format and software that can be used to view it can be found in
the 'Software'section below.
Each VICAR image file is accompanied by an attached ASCII PDS label.
The label consists of ASCII 'keyword=value' pairs describing the
important characteristics of the image.
Image Index Table
-----------------
The index table files contain keyword information about each data
product (images and maps) on the volume.
This file consists of fixed-length records in ASCII character format.
Each line is a record containing all the keywords for a particular
data product on the volume. Fields in a record are delimited by
commas. Non-numeric fields are enclosed in quotes and left-
justified, whereas numeric fields are not enclosed by any
characters and are right-justified. Multi-valued fields are
enclosed in brackets and each item in that field is separated by a
comma.
The corresponding label files for each index file details the
keyword name, data type, start byte, number of bytes, and format so
that keywords can be easily referenced and the file can be properly
read into a database.
Ancillary Data
==============
The Cassini Project produces SPICE files (spacecraft positions,
planetary positions and constants, processed pointing geometry,
spacecraft clock versus universal time, etc.) for use in observation
planning and in calculating many of the image keywords populating the
index files on this volume. These SPICE files are not included in
this ISS data archive but can be obtained from the PDS NAIF node.
Other ancillary files include the software interface specifications
related to the production of this archive volume and a list of
published references that can provide a thorough discussion of the
ISS science goals and objectives and ISS camera instrument.
Coordinate System
=================
The coordinate system adopted by the Cassini mission for satellite
mapping is the IAU 'planetographic' system, consisting of
planetographic latitude and positive west longitude, but because a
spherical reference surface is used for map projections of the
satellites, planetographic and planetocentric latitudes are
numerically equal.
Software
========
The image processing software used to create the EDR image files and
cartographic mosaics is called VICAR (Video Image Communication And
Retrieval). VICAR is an entire system of software, formats, and
procedures for image storage and processing and was developed and is
maintained by JPL's MIPS. A full explanation of VICAR, its standards,
software and reference information can be found at the website:
http://www-mipl.jpl.nasa.gov/vicar/
Information on tools for visualizing VICAR images can also be found
there. For example, the PDS-provided NASAview tool can be downloaded
from the PDS site (http://pds.jpl.nasa.gov) and used to view the raw
images.
The map sheet files are stored in Adobe PDF (Portable Document
Format). PDF is a proprietary format of Adobe Systems Incorporated
that is frequently used for distributing documents. Adobe offers a
free downloadable reader, Acrobat Reader, from their website at
http://www.adobe.com. Be sure to download the latest version of
Acrobat Reader to view the PDF files on the this volume.
Media Format
============
This volume is being delivered to the Planetary Data System (PDS)
using DVD media. Formats are based on standards for such products
established by the PDS [PDSSR1992].
|
DATA_SET_RELEASE_DATE |
2010-10-21T00:00:00.000Z
|
START_TIME |
1965-01-01T12:00:00.000Z
|
STOP_TIME |
N/A (ongoing)
|
MISSION_NAME |
CASSINI-HUYGENS
|
MISSION_START_DATE |
1997-10-15T12:00:00.000Z
|
MISSION_STOP_DATE |
2017-09-15T12:00:00.000Z
|
TARGET_NAME |
DIONE
RHEA
TETHYS
ENCELADUS
IAPETUS
MIMAS
PHOEBE
|
TARGET_TYPE |
SATELLITE
SATELLITE
SATELLITE
SATELLITE
SATELLITE
SATELLITE
SATELLITE
|
INSTRUMENT_HOST_ID |
CO
|
INSTRUMENT_NAME |
IMAGING SCIENCE SUBSYSTEM -
NARROW ANGLE
IMAGING SCIENCE SUBSYSTEM -
WIDE ANGLE
|
INSTRUMENT_ID |
ISSNA
ISSWA
|
INSTRUMENT_TYPE |
IMAGING SCIENCE SUBSYSTEM
IMAGING SCIENCE SUBSYSTEM
|
NODE_NAME |
Imaging
|
ARCHIVE_STATUS |
ARCHIVED
|
CONFIDENCE_LEVEL_NOTE |
Confidence Level Overview
=========================
The quality and completeness of the cartographic maps are determined
by a careful visual inspection by the ISS team and then a validation
by the US Geological Survey (USGS).
The quality and completeness of the archive volumes generation process
is determined by the accuracy of the archive generation software
written and employed by the CICLOPS team. This archive generation
software parses information from the data products to generate the
index files and then copies the appropriate image files, map files
and static information files prior to creating the archive volume
disk. An interface to the software allows a human user to choose
which volume to generate. The static information files are updated
as needed. These files are stored in a CVS file repository and are
reviewed as updated. An additional CICLOPS-generated script is then
run on the final volumes to check for obvious mistakes or omissions.
Additional validation software is run by PDS to ensure the disk
conforms to PDS standards.
Review
======
In order to ensure PDS-compliant products, the map volumes are
validated by a collaborative effort between the ISS/CICLOPS team,
the Imaging and Central Nodes of the PDS, and non-Cassini imaging
scientists. The ISS/CICLOPS team is responsible for producing
PDS-compliant map volumes, while the PDS personnel are responsible
for ensuring that the map volume(s) meet PDS standards. Validation
is performed on each volume by PDS using their validation tools.
ISS/CICLOPS-developed operational volume verification tools and
procedures are also utilized prior to delivery to PDS Imaging Node.
Together these verification checks ensure PDS-compliant map volumes.
A thorough review of a sample map volume and directory files is
being performed prior to the start of volume production. The peer
review of sample volume is conducted by PDS. The review serves
to validate the volume for proper structure, format, completeness,
and science usability. Any deficiencies in the reviewed map
volume found are corrected and resolved. When all correctable errors
have been resolved, production of the map volumes proceeds and
further validation is performed on a spot check basis by the both the
PDS and the ISS/CICLOPS team. Non-correctable errors are described
in the evolving errata file, errata.txt, included on each map
volume in the Root Directory.
Data Coverage and Quality
=========================
Imaging of the medium-sized icy satellites is ongoing and will
continue until the end of the Cassini mission, making it possible
to improve the image mosaics during the tour. Global mosaics consist
of mostly high-resolution Cassini images. Voyager images are used
to fill any small gaps.
The global mosaics are usually produced using images of a similar
resolution. However, some areas of the satellites are imaged at
very high resolution. These higher resolution images were processed
to separate mosaics. The data set of Phoebe is the only one that is
complete, as no more high-resolution images are expected during the
mission. Also, we will not obtain new high-resolution Enceladus
images until 2008. Therefore standard maps were generated for these
two satellites.
The Cassini spacecraft will continue its imaging campaign through
the Saturnian system. Satellite close flybys are scheduled for
Tethys, Dione, Rhea, Iapetus, and Enceladus within the nominal
mission ending in 2008. These data will be used to further improve
the existing semi-controlled mosaics and maps and also to update or
calculate initial global geodetic control networks of the Saturnian
satellites for controlled orthophoto mosaics.
A semi-controlled mosaic is composed of corrected or uncorrected
prints laid such that major ground features match their geographical
coordinates. In contrast, an uncontrolled mosaic is composed of
uncorrected photographs, the details of which have been matched
from print to print, without ground control or other orientation.
Accurate measurement and direction cannot be accomplished or
guaranteed.
Limitations
===========
The most up-to-date ellipsoid and mean radius for a body are used
in the calculations (for instance, to calculate the surface
intersection points and to fit the limb if it is available).
However, for bodies that are not good ellipsoids, like Phoebe,
this is a limitation that affects the accuracy of the mosaic.
The latitude and longitude errors on the Phoebe map is a few
degrees. For all the other bodies, the errors are much smaller.
|
CITATION_DESCRIPTION |
Porco, C.P., CASSINI ORBITER SATURN
ISSNA/ISSWA 5 MIDR VERSION 1.0,
CO-S-ISSNA/ISSWA-5-MIDR-V1.0, 2006
|
ABSTRACT_TEXT |
Images of the icy Saturnian satellites Mimas, Enceladus, Tethys,
Dione, Rhea, Iapetus, and Phoebe, derived by the Voyager and Cassini
cameras are used to produce new local highresolution image mosaics
as well as global mosaics. These global mosaics are valuable both
for scientific interpretation and for the planning of future flybys
later in the ongoing Cassini orbital tour. Furthermore, these
global mosaics can be extended to standard cartographic products.
|
PRODUCER_FULL_NAME |
CAROLYN C. PORCO
|
SEARCH/ACCESS DATA |
Atmosphere website
Imaging Planetary Image Atlas
Rings website
Imaging Online Data Volumes
|
|