| DATA_SET_DESCRIPTION |
Data Set Overview
=================
The Clementine EDR (Engineering Data Record) Image Archive
contains 88 CD-ROM volumes with more than 1.9 million images.
Each volume contains approximately 3 lunar orbits but may vary
in the number of orbits depending on the size of each orbit.
The first volume in the set begins with orbit number 32--the
start of the systematic lunar mapping phase of the mission.
The image data products for the engineering checkout and
operational rehearsal orbits (orbits 1-31), low Earth orbits,
and earth phasing loop orbits are located on the last eight
volumes at the end of the volume set. Table 1 shows the
contents of the CD-ROM volume set.
Table 1 - Volumes/Mission Phase
-------------------------------
CL_0001 through CL_0036 - Lunar Mapping/Systematic Mapping
Cycle 1 (orbits 32-164)
CL_0037 through CL_0070 - Lunar Mapping/Systematic Mapping
Cycle 2 (orbits 165-300)
CL_0070 through CL_0081 - Lunar Mapping/Post-Systematic
Mapping (orbits 301-348)
CL_0081 through CL_0085 - Lunar Mapping/Engineering Checkout
(orbits 1-30)
CL_0085 - Low Earth Orbit
CL_0086 through CL_0088 - Earth Phasing Loop A
CL_0088 - Earth Phasing Loop B
In addition to the image data, the CD-ROM volumes contain
documentation, software, timeline data, and index files that
support the collection. The 'aareadme.txt' file found in the
root directory of each volume provides the user with overview
information about the data volumes. The'document' directory
contains detailed documentation about the CD-ROM contents,
image file formats, software, and CD-ROM directory structure.
The 'errata.txt' file found in the root directory of each
volume provides the user with information about problems and
anomalies encountered with the data set during the production
of the CD-ROM volumes. Volume CL_0088, the last volume in the
set, contains the most up-to-date software and documentation.
The Clementine spacecraft imaged 100% of the lunar surface at
resolutions that ranged from 100 meters/pixel at periselene (28
degrees south latitude for observations during the first month
and 28 degrees north latitude for the second month) to 400
meters/pixel at the poles. Along the orbital track there is
approximately 15% overlap in image coverage between adjacent
images of the same spectral band. Across track overlap is
approximately 10% at the equator and increases towards the
poles.
The primary scientific objective of the Clementine imaging
observations was to provide data for lunar mineral mapping
investigations. Imaging was acquired in 12 spectral bands from
415 to 8750 nm. Pole-to-Pole NAIDR observations with solar
phase angles kept to less than 30 degrees at mid-latitudes were
the predominant viewing conditions during the two month
systematic mapping phase of the mission.
Data
====
Each Clementine EDR data file consists of a single camera
observation. The image data have been depacketized and
reformatted with standard PDS labels but are otherwise raw.
Raw data contain the geometric and radiometric characteristics
of unprocessed and unrectified data. To make full use of the
data, it is necessary to perform radiometric and geometric
processing on the data products.
The imaging sensors are framing cameras using charge couple
device (CCD) technology. The Star tracker cameras (A-STAR and
B-STAR) were principally used for spacecraft orientation. The
UVVIS, HIRES, and NIR cameras have filter wheels that allow
images to be acquired under six spectral filters. The LWIR
camera has a single spectral filter. Table 2 shows the pixel
dimensions of the images acquired by each camera and the center
wavelength of each filter wheel position. Other than the image
dimensions, the data products of each camera are identically
formatted.
Table 2 - Characteristics of each camera showing the dimension
of an image in lines (rows) and samples (columns), the number
of filter wheel positions, and the center wavelength of each
filter.
Camera/Lines/Samples/# of filt/filt.Wavelengths(Nanometers)
-----------------------------------------------------------
UVVIS 288 384 6 415,750,900,950,1000,650(broadband)
HIRES 288 384 6 415,560,650,750,650(broadband), opaque
NIR 256 256 6 1100,1250,1500,2000,2600,2780
LWIR 128 128 1 8750
A-STAR 576 384 N/A (broad band, no filter wheel)
B-STAR 576 384 N/A (broad band, no filter wheel)
Data Compression
----------------
Data compression was done onboard using a compression chip
provided by Centre National Etudes Spatiales (CNES). Onboard
processing was performed on a completed image prior to
storage on the solid state data recorder (SSDR) when the
appropriate compression flag was set. The image data are
stored on the CD-ROM volumes in the original compressed form
as sent down by the spacecraft. In order to decompress an
image, it is necessary to run the decompression software
found on the CD-ROM volumes.
The compression chip developed by MATRA under CNES
specifications is used in two modes, which could be selected
via a software uplink command. The first mode involved a
discrete cosine transformation (DCT), (named Clem-JPEG-1),
and optimized root mean square error for a nominal
compression. The second (called Clem-JPEG-2) provided visual
optimization at a fixed compression rate. In the first mode,
blocks of 8x8 pixel 8-bit data are transformed to a best fit
cosine series expansion in orthogonal row and column
directions. This algorithm tends to preserve high frequency
information with less data loss than does JPEG at the same
compression ratio for the lunar data. Total signal from the
8x8 block is preserved exactly. The nominal amount of
compression was set by limiting the scene error induced by
compression to a fraction of the camera's temporal noises.
Analysis of lunar images during the first part of the mission
showed that the quantization matrix used by the chip was
optimum for the imaging cameras.
The HIRES camera was operated in a modified JPEG mode. The
high frequency information in the HIRES scenes was spurious
(it was caused by gain non-uniformity of the intensifier
tube); eliminating high frequency content allowed higher
compression without harming the information content of the
scenes.
The average compression rate for all images obtained during
the mission was 5.5.
Processing
==========
Raw Clementine Images
---------------------
The primary data archived is the collection of raw planetary
images acquired by the Clementine mission. These data are
pristine in the sense that they contain the artifacts and the
radiometric and geometric characteristics of unprocessed and
uncorrected data. The only processing performed on the data
is to organize and format the data according to PDS
standards.
Requantization Matrices for Data Decompression
----------------------------------------------
The requantization matrix for the DCT compression algorithm
is modified throughout the course of a mapping cycle as the
viewing conditions and science requirements change. The
requantization matrix used for an image is carried as part of
the image object within a compressed image file.
Browse Images
-------------
A set of browse images is provided as part of the archive to
facilitate rapid viewing of the image collection. Browse
images can be used to visually search for areas of interest.
If a browse image shows a potentially interesting scene, the
image can be decompressed for more detailed inspection.
Browse images are not in a compressed format, but they are
reduced in size by averaging 8x8 pixel neighborhoods of the
original image. The average is stored as a single pixel in
the browse image. A browse image is stored in a secondary
object in the image file.
Histograms
----------
The histogram object is made up of a 256 element array with
each element stored as a 32-bit unsigned integer. Each
element in the histogram object contains the count of the
number of pixels in the image array that corresponds to a
specific density number (DN) value. The first element of the
histogram is the number of pixels in the image array that
have a DN value of 0. The second element contains the count
of pixels with DN value 1, the sequence thus proceeding to
the 256-th element which contains a count of the number of
pixels with a DN value of 255.
Inconsistencies may exist between the histogram statistics
found in the image histogram object and the actual image that
is decompressed on your computer platform. Subtle
differences in the floating point hardware among computer
platforms may cause the Density Number (DN) values of a
resulting decompressed image to be occasionally different
(within 1 DN) than the decompressed image used to generate
the image histogram object.
Ancillary Data and Information
==============================
Documentation
-------------
Each volume contains detailed information about the
organization and contents of the Clementine EDR CD-ROM volume
set. The documentation for the collection is found in the
'document' directory. Although each volume contains a
'document' directory, use the documents found on the last
volume (volume CL_0088) especially to obtain the most
up-to-date version of the errata.txt file.
Software
--------
Each volume contains decompression software and simple image
display programs for MAC, PCDOS or SUNOS platforms. Although
each volume contains a 'software' directory, use the software
found on the last volume (volume CL_0088) to obtain the most
up-to-date version of the software.
Image Index
-----------
Each volume contains an image index file that describes the
properties of each image found on the volume. The image
index file is an
ASCII formatted table where each row in the table corresponds
to an image and each column corresponds to an image
attribute. The attributes associated with an image include
the center latitude and longitude, camera state at the time
of the observation, spacecraft position, viewing angles, and
photometric parameters. The image index file is located in
the 'index' directory of each volume. For more information
on the image index file, refer to the documentation found in
this directory.
An updated Image Index of the entire Clementine EDR volume
set was generated by Clementine Mission Operations after
completion of the volume set. The update contains
refinements in the SPICE kernel data providing improvements
in the viewing geometry information found in the table.
Contact the PDS Imaging Node for the most up-to-date Image
Index information.
A CD-ROM volume may contain a table of missing images which
lists planned image observations that are not available on
the Clementine EDR volume set. An image is missing when (1)
the planned observation was never acquired due to a
spacecraft malfunction, (2) an interruption or error occurred
during the telemetry transmission of data to Earth, or (3)
data were lost due to problems in the ground processing
system.
Orbit Timeline
--------------
Each volume contains a 'timeline' directory housing the
timeline files for each orbit on the volume. The timeline
data describes the planned and unplanned events that occurred
during an orbit. The data, organized in chronological order,
are formatted as Microsoft EXCEL (PC Version 5.0) spreadsheet
files.
Geometric Data
--------------
The geometric data are an essential part of the archive; they
contain the data and information to characterize the
geometric properties of the imaging systems, and to fully
describe the viewing geometry of a scene. These data are
essential to geodetic, cartographic, and photometric
applications.
The geometric data are provided in NASA's SPICE kernel
formats designed by the Navigational and Ancillary
Information Facility (NAIF) at the Jet Propulsion Laboratory.
SPICE is an acronym for Spacecraft, Planet, Instrument,
C-matrix, and Event kernels.
SPICE kernels evolve and improve as further analysis is done.
Improvements could include correcting not-yet-discovered
errors and filling in missing items. For the most up-to-date
and accurate SPICE information available for the Clementine
mission please contact the Planetary Data System NAIF Node.
The geometric data found in the PDS data labels and image
index files are based on the SPICE information available at
the time of product creation. Although the geometric data
found on the CD-ROM volumes are satisfactory for search and
retrieval methods and locating images on the Lunar surface,
they are not the most up-to-date data available and thus
should not be used for precision data processing purposes.
Data reviewers have reported confusion about several
parameters that describe geometric information about the
observations. The SUB_SPACECRAFT_LATITUDE,
SUB_SPACECRAFT_LONGITUDE, SPACECRAFT_ALTITUDE, and
SUB_SPACECRAFT_AZIMUTH parameters, found in the image index
file (IMGINDX.TAB) and the image file labels, are referenced
with respect to the central body which the spacecraft is
orbiting, not necessarily the target of the observation.
During the lunar mapping phase of the mission, the central
body is the Moon. Thus, if the target is the Earth, the
above listed parameters are referenced with respect to the
Moon and not Earth.
Coordinate System
-----------------
J2000 (also called EME2000) is the inertial reference system
used to specify observational geometry. Latitude and
longitude coordinates of target are planetocentric.
For a complete description of the coordinate system used for
the Clementine EDR data set, refer to [ACTON1996].
Media Format
------------
The disk has been formatted so that a variety of computer
systems (e.g. IBM/PC compatible, Macintosh, Sun) may access
the data. Specifically, it is formatted according to the ISO
9660 level 1 Interchange Standard. For further information,
refer to the ISO 9660 Standard Document: Reference Number ISO
9660-1988, 15 April 1988. The extended attribute records
(XAR) supported by the ISO are not used in this volume set.
The lack of XARs on a file only affects the VAX/VMS user
community. It will be necessary for VAX/VMS users to use the
VMS CONVERT utility to convert document and text files before
they can be satisfactorily accessed. VAX/VMS users can
contact the PDS Imaging Node for support of the Clementine
EDR archive.
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