| DATA_SET_DESCRIPTION |
Data Set Overview
=================
This data set contains raw 750-nm filter images of Mars
acquired by the Deep Impact Medium Resolution Visible CCD (MRI) for the
EPOCh project during the second cruise phase of the EPOXI mission. One
set of observations was acquired on 20-21 November 2009 to characterize
Mars as an analog for extrasolar planets. The observing period lasted
approximately 24 hours, and one MRI image was taken simultaneously with
the first north/south scan of the HRI IR spectrometer at half-hour
intervals to provide context for the spectral scans.
Required Reading
---------------
The documents detailed below are essential for the understanding and
interpretation of this data set. Although a copy of each document is
provided in the DOCUMENT/ directory of this data set, the most recent
version is archived in the Deep Impact and EPOXI documentation set,
DI-C-HRII/HRIV/MRI/ITS-6-DOC-SET-V3.0, available online at
http://pds.nasa.gov.
EPOXI_SIS.PDF
- The Archive Volume and Data Product Software Interface
Specifications document (SIS) describes the the data set, the
science data products, and defines keywords in the PDS labels.
CALIBRATION_PAPER_DRAFT.PDF
- The Deep Impact instrument calibration paper by Klaasen, et al.
(2008) [KLAASENETAL2006] describes how the instruments were
calibrated for Deep Impact and similarly for EPOXI and explains
the calibration process used for both missions. The published
version should be available online in the Review of Scientific
Instruments by the American Institute of Physics. The EPOXI
archive provides only an incomplete draft.
INSTRUMENTS_HAMPTON.PDF
- The Deep Impact instruments paper by Hampton, et al. (2005)
[HAMPTONETAL2005] provides very detailed descriptions of the
instruments.
EPOCH_MARS_OBS.PDF
- This document describes of the EPOCh Mars observations
although most of the information is captured in this data set
catalog file you are reading.
EPOCH_MARS_SEQ_2009.PDF
- This document provides pointing and sequencing information
for the EPOCh Mars observations in 2009, including descriptions
of the HRII scans of Mars (scan direction, rate, etc.).
EPOCH_OVERVIEW.PDF
- This presentation provides an overview of the EPOCh phase of
the EPOXI mission.
MRI_2_EPOXI_MARS.TAB
- This ASCII table provides image parameters such as the mid-obs
Julian date, exposure time, mission activity type, and
description or purpose for each observation (i.e., data product)
in this data set. This file is very useful for determining which
data files to work with.
Related Data Sets
-----------------
The following PDS data sets, available online at http://pds.nasa.gov,
are related to this one and may be useful for research:
DIF-M-MRI-3/4-EPOXI-MARS-V1.0
- Calibrated MRI Mars observations (context images)
DIF-M-HRII-2-EPOXI-MARS-V1.0
DIF-M-HRII-3/4-EPOXI-MARS-V1.0
- Raw and calibrated 1.05- to 4.8-micron HRI IR spectra of Mars,
covering the same observing period as this data set
DIF-M-HRIV-2-EPOXI-MARS-V1.0
DIF-M-HRIV-3/4-EPOXI-MARS-V1.0
- Raw and calibrated HRIV visible CCD Mars observations at
350, 450, 550, 650, 750, 850, and 950 nm, covering the
same same observing period as this data set
DI-C-HRII/HRIV/MRI/ITS-6-DOC-SET-V3.0
- Deep Impact and EPOXI documentation set
DIF-C/E/X-SPICE-6-V1.0
- EPOXI SPICE kernels, available at end of EPOXI mission
DIF-CAL-HRII/HRIV/MRI-6-EPOXI-TEMPS-V1.0
- HRII, HRIV, and MRI instrument thermal telemetry data for EPOXI
which may be useful for determining how temperature fluctuations
affect the science instruments, in particular the IR spectrometer
Processing
==========
The raw two-dimensional FITS CCD images and PDS labels in this data
set were generated by the Deep Impact/EPOXI data pipeline, maintained
by the project's Science Data Center (SDC) at Cornell University.
The FITS data were assembled from raw telemetry packets sent down by
the flyby spacecraft. Information from the embedded spacecraft
header (the first 100 bytes of quadrant A image data) was extracted
and stored in the primary FITS header. Geometric parameters were
computed using the best available SPICE kernels and the results were
also stored in the FITS header. If telemetry packets were missing,
the corresponding pixels were flagged as missing in the quality map
included as a FITS image extension. The quadrant nomenclature and
the image quality map are described in the Deep Impact instrument
calibration document and the EPOXI SIS document included in this data
set. The SDC did not apply any type of correction or decompression
algorithm to the raw data.
Data
====
FITS Images and PDS Labels
--------------------------
Each raw MRI image is stored as FITS. The primary data unit contains
the two-dimensional CCD image. It is followed by one image extension
that contains a two-dimensional pixel-by-pixel quality map. This
extension uses one byte of eight bit flags to indicate the quality of
each pixel in the primary image. The data label provides a short
description of each bit. For more information about the FITS primary
image and its extension or for examples of how to access and use the
quality flags, refer to the EPOXI SIS document or the Deep Impact
instrument calibration document.
Each FITS file is accompanied by a detached PDS data label. The
EPOXI SIS document provides definitions for the keywords found in a
data label.
File Naming Convention
----------------------
The naming convention for the raw data labels and FITS files is
MVyymmddhh_eeeeeee_nnn.LBL or FIT where 'MV' identifies the MRI
instrument, yymmddhh provides the UTC year, month, day, and hour at
the mid-point of the observation, eeeeeee is the exposure ID
(OBSERVATION_ID in data labels), and nnn provides the image number
(IMAGE_NUMBER in the data labels) within the exposure ID.
Up to 999 individual images or frames can be commanded for one
exposure ID. Therefore, nnn in the file name provides the
sequentially increasing frame number within an exposure ID and
corresponds to IMAGE_NUMBER in the data labels. For example, if 8
frames were commanded for a scan with an exposure ID of 1000000, the
first FITS file name would be MV09112011_1000000_001.FIT and the
last would be MV09112011_1000000_008.FIT.
Image Compression
-----------------
Although raw data numbers for MRI frames could be compressed on
board the flyby spacecraft by use of a lookup table then downlinked,
processed, and archived in the same format, Mars images acquired
during the time period covered by this data set were never
compressed. Therefore the COMPRESSED_IMAGE_VALUE keyword in the
data labels is always set to 'UNCOMPRESSED'. For more information
about this topic, see the image compression section of the Deep
Impact instrument calibration documents.
Image Orientation
-----------------
A true-sky 'as seen by the observer' view is achieved by displaying
the image using the standard FITS convention: the fastest-varying
axis (samples) increasing to the right in the display
window and the slowest-varying axis (lines)
increasing to the top. This convention is identified in the data
labels: the SAMPLE_DISPLAY_DIRECTION keyword is set to RIGHT and
LINE_DISPLAY_DIRECTION to UP.
The direction to celestial north, ecliptic north, and the Sun is
provided in data labels by CELESTIAL_NORTH_CLOCK_ANGLE,
ECLIPTIC_NORTH_CLOCK_ANGLE, and SUN_DIRECTION_CLOCK_ANGLE keywords
and are measured clockwise from the top of the image when is
displayed in the correct orientation as defined by
SAMPLE_DISPLAY_DIRECTION and LINE_DISPLAY_DIRECTION. Please note
the aspect of the North celestial pole in an image can be computed
by adding 90 degrees to the boresight declination given by
DECLINATION in the data labels.
For a comparison of the orientation FITS image data from the three
science instruments, see the quadrant nomenclature section of the
Deep Impact instrument calibration document. Also the EPOXI SIS
has a brief discussion of this topic.
Instrument Alignment
--------------------
For a comparison of the field of view and the relative boresight
alignment of MRI to the High Resolution Instrument Visible CCD
(HRIV) and the slit of the High Resolution IR Imaging Spectrometer
(HRII), see the relative boresight alignments section of the Deep
Impact instrument calibration document.
Parameters
==========
Data Units
----------
Raw image data have units of raw data numbers.
Imaging Modes
-------------
One image mode was used for all MRI Mars observations:
X-Size Y-Size
Mode Name (pix) (pix) Comments
---- ------ ------ ------ ---------------------------------------
2 SF1 512 512 Sub-frame, shuttered
All modes are unbinned. For a thorough description of the imaging
modes, please see the Deep Impact instruments document or the Deep
Impact instrument calibration document. Also the EPOXI SIS has a
brief discussion of this topic.
Most image modes have a set of bias overclock rows and columns,
located around the edges of the image array. All overclock pixels
were excluded from the calculation of the values for MINIMUM,
MAXIMUM, MEDIAN, and STANDARD_DEVIATION in the data labels. These
overclock areas described in the Deep Impact instruments document
and the Deep Impact instrument calibration document.
Filters
-------
One filter was used for all MRI Mars observations:
Filter Center Width
# Name (nm) (nm) Comments
- ---------- ----- ----- -------------------------------
4 RED 750 100 For context
For more information about the filters, see the Deep Impact
instruments document or the Deep Impact instrument calibration
document. Also the EPOXI SIS has a brief discussion of this topic.
Time- and Geometry-Related Keywords
-----------------------------------
All time-related keywords in the data labels, except
EARTH_OBSERVER_MID_TIME, are based on the clock on board the flyby
spacecraft. EARTH_OBSERVER_MID_TIME provides the UTC when an
Mars-based observer should have been able to see an event recorded
by the instrument.
For Mars observations, sub-spacecraft and sub-solar longitude and
latitude coordinates (planetocentric, body-fixed rotating) are
provided, when available, in the data labels by
SUB_SPACECRAFT_LONGITUDE, SUB_SPACECRAFT_LATITUDE,
SUB_SOLAR_LONGITUDE, and SUB_SOLAR_LATITUDE.
The SDC pipeline was not able to automatically determine the proper
geometric information for the target of choice in some cases. When
these parameters could not be computed, the corresponding keywords
in the data labels are set to a value of unknown, 'UNK'. Also if
GEOMETRY_QUALITY_FLAG is set to 'BAD' or GEOMETRY_TYPE is set to
'PREDICTED' in the PDS labels, then this indicates the geometry
values may not be accurate and should be used with caution. The
value 'N/A' is used for some geometry-related keywords in the data
labels because these parameters are not applicable for certain
calibration targets.
Observational geometry parameters provided in the data labels were
computed at the epoch specified by the mid-obs UTC, IMAGE_MID_TIME,
in the data labels. The exceptions are the target-to-sun values
evaluated at the time light left the target that reached the
spacecraft at mid-obs time, and the earth-observer-to-target values
evaluated at the time the light that left the target, which reached
the spacecraft at mid-obs time, reached Earth.
Ancillary Data
==============
The UTC and geometry values included in the data labels and FITS headers
were computed using the best available SPICE kernels at the time the
products were generated. The final, best SPICE kernels will be posted
on the NAIF/SPICE web site at http://naif.jpl.nasa.gov/naif/ and
archived in the PDS data set DIF-C/E/X-SPICE-6-V1.0 after the end
of the EPOXI mission.
Coordinate System
=================
Earth Mean Equator and Vernal Equinox of J2000 (EME J2000) is the
inertial reference system used to specify observational geometry
parameters in the data labels, unless specified otherwise (e.g,
SUB_SPACECRAFT_LONGITUDE).
Software
========
The observations in this data set are in standard FITS format with PDS
labels, and can be viewed by a number of PDS-provided and commercial
programs. For this reason no special software is provided with this
data set.
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