| DATA_SET_DESCRIPTION |
Data Set Overview
=================
The High Resolution Imaging Science Experiment (HiRISE) is one of
the remote sensing instruments on the Mars Reconnaissance Orbiter
(MRO) spacecraft that acquires orbital observations of the Martian
surface during a two earth-year primary mapping phase. MRO,
successfully launched in August 2005, arrived at Mars in March
2006. Following orbit insertion the spacecraft went into an
aerobraking period to achieve a 250 x 315 kilometer near-polar
orbit suitable for the Primary Science Phase (PSP) mapping that
started in November 2006. Since the start of PSP HiRISE has been
continuously operating acquiring 10-20 observations per day.
The HiRISE team is responsible for maintaining an updated dataset
of the best version of its science data until meaningful
changes in data calibration no longer occur and to release data in
an appropriate manner for public access including their final
deposition to NASA's Planetary Data System (PDS). In carrying out
these responsibilities, the HiRISE team creates two types of
standard data products: 1) Experiment Data Record (EDR) products
and 2) Reduced Data Record (RDR) Products. This document describes
the RDR standard products.
These Reduced Data Record (RDR) products are radiometrically-
corrected images resampled to a standard map projection. They
are formatted and organized according to the standards of the PDS.
The RDR image is stored in the JPEG2000 format recently accepted
by the PDS. The JPEG2000 images are accompanied by a PDS detached
label providing supporting information about the observation.
The HiRISE RDR products comply with the PDS standards for file
formats and labels, specifically using the PDS image object
definition. The RDR image files, formatted according to the
JPEG2000 standard, use 'JP2' as their filename extension. They are
accompanied by PDS labels; files that have the same name as the
image data file but use 'LBL' for their filename extension. The
label file provides image data characterization and science
metadata information about the observation. Additionally, the
ancillary data files that accompany the RDR products and the
archive volume structure are in conformance with PDS standards.
RDR image data are stored in the JPEG2000 ISO/IEC Part 1 standard
format (http://www.jpeg.org/jpeg2000/), which was accepted by the
PDS standard in October 2005. The JPEG2000 standard offers
benefits distinctly advantageous for storage and access to very
large images. With HiRISE RDR products reaching sizes exceeding
30,000 x 70,000 pixels the use of JPEG2000 was recognized as a
suitable solution for the storage and distribution of these data
products. Advantages include excellent compression performance,
multiple resolution levels from a single image data set,
progressive decompression quality layers, lossless and lossy
compression (HiRISE RDR products use lossless compression per the
PDS Standard), pixel datum precision up to 38 bits, multiple image
components (or bands), and selective image area access. These
features are achieved by the use of a sophisticated image coding
system based on discrete wavelet transforms (DWT) combined with
other coding techniques to generate a JPEG2000 codestream that can
be rendered to image pixel rasters using
inverse transform algorithms.
Processing
==========
Science data from the MRO payload experiments are packetized on
the spacecraft, transmitted to Earth through the Deep Space
Network, and sent to the Jet Propulsion Laboratory (JPL) through
ground communications. The JPL Multi-Mission Operations Facility
converts the packetized data back to the original science data
format as produced by the instruments. For HiRISE observations, a
raw science product is created for each CCD/Channel involved in
the observation. The data are stored at JPL's Raw Science Data
Server (RSDS) for access by the science teams.
At the HiRISE Operations center (HiROC) we have developed a ground
data system that provides automated methods for retrieving and
processing our images. Science data are automatically retrieved
from the RSDS and passed to a series of pipeline procedures
managed under the Conductor environment
(http://pirl.lpl.arizona.edu/software/Conductor.shtml). The
pipelines generate intermediate products used for image evaluation
and standard data products for science analysis. Additionally, the
pipelines populate HiRISE-catalog EDR and RDR product tables and
observation geometry tables with relevant metadata. The product
and geometry tables are used to generate index tables provided as
part of the product distribution to the PDS. The HiRISE team verifies
observations were properly acquired and science objectives
achieved. Missed targets or observations with poor viewing
conditions are flagged for reacquisition at a later time. HiROC
uses the Integrated Software for Imagers and Spectrometers (ISIS)
system in the pipeline processing. ISIS contains a wide range of
tools including radiometric calibration and cartographic
processing procedures. The ISIS components applicable to HiRISE
include radiometric calibration, map projection transformation,
image mosaicking, camera pointing correction, and general image
enhancement, display, and analysis tools. For more information on
this freely available image analysis package, see the ISIS web
site (http:// isis.astrogeology.usgs.gov/).
HiROC's pipeline processing starts when the FEI_WatchDog procedure,
responsible for periodically monitoring the RSDS, determines a raw
science data file is ready to be downloaded from the RSDS and
passes the name of the product to the HiDog pipeline (Downlink
Organizer). The HiDog pipeline retrieves the data product then
submits the file name to the EDRgen pipeline (EDR generator) for
creating the EDR product and populating the EDR product table with
metadata about the product. The HiRISE Observation software used to
products is described in detail at
http://pirlwww.lpl.arizona.edu/software/HiRISE/
and can be obtained on request. The EDR_Stats pipeline creates an
ISIS file and generates image statistics that are placed in the EDR
products table. The HiCal pipeline performs the radiometric
correction (see Section 4.1.1), and generates a browse and
thumbnail image of the EDR product to be used by the HiRISE and
PDS Imaging Node data-distribution web services. When the HiCal
pipeline determines two channel files of a CCD have been
calibrated the file names are passed on to the HiStitch pipeline
for creating an intermediate CCD image file. HiStitch additionally
adjusts the channels to radiometrically match at the seam where
the two channels come together. When the HiStitch pipeline
determines all of the observation's CCDs have been stitched
together for a filter set then the HiccdStitch pipeline is invoked
to create an intermediate product with the CCDs stitched together
to form a single image for the color filter. HiccdStitch
additionally adjusts the CCD images to radiometrically match the
overlapping areas of adjacent CCDs. Finally HiccdStitch creates an
intermediate JPEG image for evaluation by the HiRISE team.
At this point in the processing the EDR-validation step occurs. To
continue the pipeline processing the reconstructed SPK and CK
SPICE kernels, providing information about the observing viewing
geometry and spacecraft ephemerides, need to be retrieved from the
NAIF Node though HiROC's HiSPICE subsystem. Reconstructed SPICE
kernels are generally provided to the MRO science teams one to two
weeks after the observation was acquired. The HiGeomInit pipeline
extracts the spacecraft ephemeris kernel (SPK) and C-matrix
pointing kernel (CK) data from the SPICE files and transfers the
data to the CCD image files for geometry processing by the
pipelines that follow. Additionally HiGeomInit populates the
observation geometry table with viewing geometry and coordinate
metadata. The RedGeom and ColorGeom pipelines perform geometric
processing on individual CCD images. The RedMosaic and ColorMosaic
pipelines mosaic the projected CCD images to form an observational
image. Additionally these pipelines create RDR-product browse and
thumbnail jpeg images for HiRISE and PDS Imaging Node web-based
distribution services. The last pipeline step, RDRgen, creates
the JPEG2000 formatted JP2 image file accompanied by a PDS detached
label file and populates the RDR product table with information about
the product. The software for converting a raw PDS file with an
attached label to PDS label and JP2 files is available on request.
Following a final validation step the EDR and RDR
products are releasable to the PDS and science community.
Radiometric Calibration Processing
----------------------------------
The radiometric calibration-correction procedure is described here
at a high level. A detailed description will be provided in a
future HiRISE calibration paper. The radiometric calibration
correction is performed on each individual HiRISE channel file
(EDR) correcting for instrument offset, dark current, gain, then
converting to I/F reflectance. The first step in the calibration,
carried out by the ISIS hiclean program, corrects for instrument
dark current and offset. The hiclean program uses the ancillary
calibration data (dark and mask pixels that accompany the science
data to compute corrections in both the column (sample) and row
(line) directions. The mask pixels, positioned at the start of the
instrument output, provide dark current information for each
column. The dark pixels, positioned at the end of each image row,
capture the time dependent dark current and offset instrument
drift.
The ISIS hical program then applies an intra-channel B0 (additive
dark current matrix) and A0 (multiplicative gain matrix)
correction for each column in the image array. The hical then
converts the pixel values to I/F (intensity/flux, I/F = 1 for a
100% ideal lambertian reflector viewed normal to the surface) as
described below:
For:
H = dark current and offset corrected image, output of hiclean
B0 = intra-channel dark current correction (TDI & BIN dependent)
A0 = intra-channel gain correction (TDI and BIN dependent)
G = global gain correction, normalizes CCD/channels
L = observation line time
I = I/F conversion factor at Sun-Target distance of 1.5 AU
AU = Mars-to-Sun distance (AU) at time of observation
Z = radiometrically corrected image in I/F units
The correction is:
Z = ([H-(B0_L)]/L)_A0_G*I*(1.5/AU)2
Instrument instabilities result in radiometric mismatches requiring
additional corrections for the varying column-to-column, channel-to-
channel, and CCD-to-CCD sensitivities. Residual column-to-column
variations are corrected by first computing the mean value for each
column in an image array. The mean-value one-dimensional array is then
high-pass filtered to eliminate low-frequency information due to scene
content. The result of the high pass filter is then subtracted from
the image array. CCD channels are adjusted to radiometrically match at
the seam where the two channels come together (performed by the
HiStitch pipeline). The CCDs are then radiometrically matched one to
the other by matching the overlapping areas of adjacent CCDs (
performed in the HiccdStitch pipeline).
Geometry Processing
-------------------
There will typically be two RDR standard products per observation: a
single-color RDR product built from the operating red-filter CCDs, and
0a three-color RDR product if the blue-green and near-infrared CCDs
were additionally operating. In rare cases a two-color RDR product
will be created if only two color filters were commanded.
The geometric processing corrects for the optical distortion and
projects the observation from spacecraft viewing orientation to a map
coordinate system. For RDR products the Equirectangular or Polar
Stereographic projections are used. The geometry processing, carried
out by ISIS program cam2map, uses cubic convolution resampling.
Geometry processing employs the NAIF toolkit
(http://naif.jpl.nasa.gov) and uses reconstructed SPICE kernels
generated by the MRO project. The geometry processing uses the MOLA
Digital Terrain Model to improve the camera pointing intercept
position on the Martian surface.
In the geometric processing, individual channel images are stitched
together to form CCD images using the ISIS program histitch. The
spiceinit program searches through the available NAIF kernel set and
applies planet and spacecraft ephemeris data to establish geometric
properties of each CCD image CCD images are then individually map
projected with camp2map and mosaicked together using himos forming an
image of the entire observation. Resulting image maps vary in size
depending on the number of CCDs commanded, number of lines acquired
and the binning mode of the images. RDR products can be very large, at
times exceeding 30,000 x 70,000 pixels. Observations with mixed
binning modes are resampled to the same pixel scale depending on the
minimum binning used in the observation. For the Transition Orbit
Phase (TRA) and Primary Science Phase (PSP), observations with
unbinned imaging are uniformly mapped to a constant 0.25 m/pixel
resolution (0.50 m/pixel for minimum binning 2 and 1.0 for binning 4).
The Aerobraking phase images (AEB) are mapped to a pixel scale
depending on the spacecraft altitude and the minimum binning.
For three-color imaging additional processing steps are required to
create the three-color RDR products. Spacecraft jitter exists at a
higher frequency than can be captured by the reconstructed pointing
kernels. The color CCDs see a point on the planet surface separated
by ~120 milliseconds resulting in jitter-induced pointing
misalignments not captured by the reconstructed pointing matrix. To
minimize color misregistration the blue-green and near-infrared
filters are spatially matched through a two-step empirical approach.
In the first step the blue-green and near-infrared filter CCD images
(usually acquired at a higher binning level than the red-filter CCDs)
are scaled to match the binning of the red-filter CCD imaging. Next,
an ISIS program, hijitreg, applies an image coregistration process
constructing a control network that spatially maps the blue-green and
near-infrared filter imaging to the red filter imaging. The control
network is provided to the second step responsible for resampling the
blue-green and near-infrared filter images to the red. The program,
slither, performs a one-dimensional cubic-spline transformation
performing translational shifts on otherwise undistorted individual
lines. Once the blue-green and near-infrared images are spatially
registered to match the red imaging, the images go through the same
geometric processing to create a map-projected image as described
above. The BANDWIDTH keyword in the PDS labels identifies the color
filters used in the image product. The CENTER_FILTER_WAVELENGTH and
BANDWIDTH keywords provide information about the spectral range of
each filter The storage order for the the three-color products is
Near Infrared (band 1), Red (band 2), and blue-gree (band 3).
Data
====
The HiRISE EDR products act as the input source to the RDR
processing.
Ancillary Data
==============
Generation of the RDR products relies on the MRO-project deliveries
for the Spacecraft Ephemeris (SPK kernels) and MRO spacecraft pointing
files (CK kernels)
Coordinate System & Cartographic Standards
==========================================
The HiRISE RDR products are compatible with the cartographic standards
and mapping conventions used by the MRO CRISM map products. When
spatially registering map products produced by the two instrument
teams only a translation and scale change are required. The
coordinate system used is planetocentric latitude and east positive
longitude direction. The planetocentric latitude is the angle from the
equator to a point on the surface of an oblate planet. The longitude
increases from west to east (left to right).
The planetary constants used in the camera model to produce the HiRISE
RDR products are obtained from the NAIF SPICE planetary constants
kernel pck0008.tpc. The Mars constants of particular importance are
the right ascension and declination of the pole, the prime meridian,
rotation rate, and radii. The constants used are:
BODY499_POLE_RA = ( 317.68143 -0.1061 0. )
BODY499_POLE_DEC = ( 52.88650 -0.0609 0. )
BODY499_PM = ( 176.630 350.89198226 0. )
BODY499_RADII = ( 3396.19 3396.19 3376.20 )
Additionally, the SPICE kernel de405.bsp was used for the ephemeris
data for Mars.
Two map projections are used in the HiRISE RDR products:
Equirectangular and Polar Stereographic.
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