NSSDCA ID: PSSB-00600
Availability: Archived at NSSDC, accessible from elsewhere
This description was generated automatically using input from the Planetary Data System.
This dataset contains calibrated, 750-nm filter images of Earth acquired by the Deep Impact Medium Resolution Visible CCD (MRI) during the EPOCh and Cruise 2 phases of the EPOXI mission. The MRI instrument was only used during the first Earth observing period on 18-19 March 2008 and the last two on 27-28 March and 04-05 October 2009. Each 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 serve as context spectra. On 27-28 September 2009 during the first attempt at Earth south polar observations, a full set of MRI context images was acquired although the HRII and HRIV instruments were turned off by fault protection shortly after the sequence started. Version 2.0 includes the application of a horizontal destriping process, revised electronic crosstalk calibration files, and a corrected spacecraft clock algorithm to remove a known systematic error at the subsecond level in the conversion of the spacecraft times to UTCs. 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-V4.0, 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. EPOXI_CAL_PIPELINE_SUMM.PDF - The EPOXI Calibration Pipeline Summary provides an overview of the final version of the calibration pipeline that generated the data products in this dataset. For a thorough discussion of the pipeline, see 'EPOXI Instrument Calibration' by Klaasen, et. al. (2013) [KLAASENETAL2011]. INSTRUMENTS_HAMPTON.PDF - The Deep Impact instruments paper by Hampton, et al. (2005) [HAMPTONETAL2005] provides very detailed descriptions of the instruments. EPOCH_EARTH_OBS.PDF - This document describes of the EPOCh Earth observations although most of the information is captured in this data set catalog file you are reading. EPOCH_EARTH_SEQ_2008.PDF EPOCH_EARTH_SEQ_2009.PDF - These documents provide pointing and sequencing information for the EPOCh Earth observations in 2008 and 2009, including descriptions of the HRII scans of Earth (scan direction, rate, etc.). EPOCH_OVERVIEW.PDF - This presentation provides an overview of the EPOCh phase of the EPOXI mission. MRI_3_4_EPOXI_EARTH.TAB - This ASCII table provides image parameters such as the mid-obs Julian date, exposure time, filter, 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. Publications of the scientific results from the Earth observations in this data set include Cowan, et al. (2009) [COWANETAL2009], Livengood, et al. (2009) [LIVENGOODETAL2009], and Crow, et al. (2011) [CROWETAL2011]. Related Data Sets ----------------The following PDS data sets are related to this one and may be useful for research: DIF-E-MRI-2-EPOXI-EARTH-V1.0 - Raw MRI Earth observations (context images) DIF-E-HRII-2-EPOXI-EARTH-V1.0 DIF-E-HRII-3/4-EPOXI-EARTH-V2.0 - Raw and calibrated 1.05- to 4.8-micron HRI IR spectra of Earth, covering the same observing periods as this data set (no IR spectra were acquired when the HRII and HRIV instruments were prematurely turned off at the beginning of the first attempt of an Earth south polar observation on 27 Sep 2009) DIF-E-HRIV-2-EPOXI-EARTH-V1.0 DIF-E-HRIV-3/4-EPOXI-EARTH-V2.0 - Raw and calibrated HRIV visible CCD Earth observations at 350, 450, 550, 650, 750, 850, and 950 nm, covering the same observing periods as this data set except 27-28 Sep 2009 (only seven HRIV frames were acquired before that instrument was prematurely turned off at the beginning of the first attempt of an Earth south polar observation on 27 Sep 2009) DIF-C/E/X-SPICE-6-V1.0 - EPOXI SPICE kernels 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 DI-C-HRII/HRIV/MRI/ITS-6-DOC-SET-V4.0 - Deep Impact and EPOXI documentation set including a draft of the Deep Impact instrument calibration paper by Klaasen, et al. (2008) [KLAASENETAL2006] Processing ========== The calibrated two-dimensional FITS CCD images and PDS labels in this dataset were generated by the Deep Impact/EPOXI data pipeline, maintained by the project's Science Data Center (SDC) at Cornell University. The final version of the pipeline, dated December 2012, was used. Known limitations and deficiencies of the pipeline are discussed in the EPOXI Calibration Pipeline Summary document in this dataset or by Klaasen, et al. (2013) [KLAASENETAL2011]. For each CCD image, the pipeline generates two types of calibrated products: - Uncleaned radiance data provided in units of Watts/(meter**2 steradian micron) and identified by the mnemonic 'RADREV'. The RADREV data are considered to be reversible because the calibration steps can be backed out to return to the original, raw data numbers. A RADREV image can be converted to unitless I-over-F by multiplying by the value assigned to the DATA_TO_IOVERF_MULTIPLIER keyword in the PDS label. Alternatively, a RADREV image can be converted from radiance units to calibrated data numbers by multiplying by the value assigned to the DATA_TO_DN_MULTIPLIER in the PDS label. - Irreversibly cleaned radiance data provided in units of Watts/(meter**2 steradian micron) and identified by the mnemonic 'RAD'. The RAD data are considered to be irreversible because the calibration steps, such as smoothing over bad pixels, cannot easily be backed out to return to the original, raw data numbers. A RAD image can be converted to unitless I-over-F by multiplying by the value assigned to the DATA_TO_IOVERF_MULTIPLIER keyword in the PDS label. Alternatively, a RAD image can be converted from radiance units to calibrated data numbers by multiplying by the value assigned to the DATA_TO_DN_MULTIPLIER in the PDS label (though interpolated pixels will not be real data). Please note that values in the overclock rows and columns bordering the active CCD area are set to 0 in the RAD product. The calibration pipeline performed the following processes, in the order listed, on the raw FITS data to produce the RADREV and RAD products found in this data set (the process uses the image mode and filter to select the appropriate set of calibration files): - Decompression of compressed images (reversible) - Correction for bias (reversible) - Subtraction of a dark frame (reversible) - Removal of horizontal, instrumental striping (reversible) - Removal of electronic cross-talk (reversible) - Application of a normalized flat field (reversible) - Removal of CCD transfer smear (reversible) - Conversion of data numbers to units of radiance for an absolute, radiometric calibration that is reversible (RADREV) - Interpolation over bad and missing pixels identified in the RADREV data to make a partially cleaned, irreversible, radiometric calibration with units of radiance (RAD); Steps for despiking (i.e., cosmic ray removal) and denoising the data which are part of the RAD stream were not performed because the existing routines are not robust - Calculation of multiplicative factors to convert a RADREV or RAD image to I-over-F As part of the calibration process, the pipeline updated the pixel-by-pixel image quality map, the first FITS extension, to identify: - Pixels where the raw value was saturated, - Pixels where the analog-to-digital converter was saturated, - Pixels that were ultra-compressed and thus contain very little information, and - Pixels considered to be anomalous as indicated by bad pixel maps (missing pixels were identified when the raw FITS files were created). The pipeline also created a FITS image extension to capture the signal-to-noise ratio map and another extension to capture the values used to remove horizontal striping. The calibration steps and files applied to each raw image are listed in the PROCESSING_HISTORY_TEXT keyword in the PDS data label. Data ==== FITS Images and PDS Labels -------------------------Each calibrated image is stored as FITS. The primary data unit contains the two-dimensional CCD image which is followed by two image extensions that are two-dimensional pixel-by-pixel maps providing additional information about the CCD image: - The first extension uses one byte of eight, bit flags to describe the quality of each pixel in the primary image. The PDS data label defines the purpose of each bit. - The second extension provides a signal-to-noise ratio for each pixel in the primary image. - The third extension contains the two columns of DN values that were subtracted from every non-overclock column in the left and right halves of the primary image array by the stripe removal process; since destriping may remove scattered light from very bright sources, the EPOXI SIS document describes how to 'restripe' an image if needed. 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 and provides more information about the FITS primary image and the extensions. Many values in a data label were extracted from FITS image header keywords which are defined in the document EPOXI_FITS_KEYWORD_DESC.ASC found in the Deep Impact and EPOXI documentation dataset, DI-C-HRII/HRIV/MRI/ITS-6-DOC-SET-V4.0. File Naming Convention ---------------------The naming convention for the raw data labels and FITS files is MVyymmddhh_eeeeeee_nnn_rr.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), nnn provides the image number (IMAGE_NUMBER in the data labels) within the exposure ID, and rr identifies the type of reduction: RR for RADREV data (reversibly calibrated, radiance units) R for RAD data (partially cleaned RADREV data, radiance units) 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 32 frames were commanded for a scan with an exposure ID of 1000000, the first FITS file name would be MV08031818_1000000_001_RR.FIT and the last would be MV08031818_1000000_032_RR.FIT. Image Compression ----------------All calibrated data products are uncompressed. If an associated raw data product was compressed on-board the flyby spacecraft (and thus received on the ground and archived as compressed) then the calibration pipeline used one of four 8-bit lookup tables to decompress the raw image. See the EPOXI SIS and EPOXI Hartley 2 Calibration Pipeline Summary documents as well as Klaasen, et al. (2008) [KLAASENETAL2006] for more information. 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 it 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 of FITS image data from the three science instruments, see the quadrant nomenclature section of the the EPOXI SIS document. 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 instrument alignment section of the EPOXI SIS document or section 5.1 of Klaasen, et al. (2013) [KLAASENETAL2011]. Parameters ========== Data Units ---------The calibrated RADREV and RAD image data have units of radiance, W/(m**2 steradian micron). Imaging Modes ------------One image mode was used for all MRI Earth observations: X-Size Y-Size Mode Name (pix) (pix) Comments ---- ------ ------ ------ --------------------------------------2 SF1 512 512 Sub-frame, shuttered All modes are unbinned. 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 included with this dataset. Filters ------A summary of the MRI filters used for the Earth observations is provided below. For more information about the filters, see the Deep Impact instruments document. For the effective center wavelengths and the corresponding full-width-half-max values see Klaasen, et al. (2013) [KLAASENETAL2011]. Filter Center Width # Name (nm) (nm) Comments - ---------- ----- ----- ------------------------------4 RED 750 100 For context 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 Earth-based observer should have been able to see an event recorded by the instrument. For Earth 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 geometric parameters included in the data labels and FITS headers were computed using the best available SPICE kernels at the time the data products were generated. Most kernels are available in the EPOXI SPICE dataset, DIF-C/E/X-SPICE-6-V1.0; others that had not yet been archived in the PDS when this dataset was produced are available online at the Operational Flight Project Kernels website maintained by the NASA Navigation and Ancillary Information Facility (NAIF), http://naif.jpl.nasa.gov/naif/data_operational.html. 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.
These data are available on-line from the Planetary Data System (PDS) at:
http://pdssbn.astro.umd.edu/holdings/dif-e-mri-3_4-epoxi-earth-v2.0/
Questions and comments about this data collection can be directed to: Dr. David R. Williams
Name | Role | Original Affiliation | |
---|---|---|---|
Dr. Michael F. A'Hearn | Data Provider | University of Maryland |