Data Set Overview : This data set contains raw, 1.05- to 4.8-micron spectra of Mars acquired by the High Resolution Infrared Spectrometer (HRII) 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 spectra were acquired twice per hour.  At every half hour of each observing period, the spacecraft slewed across the Mars while the IR spectrometer recorded data; these scans were performed three times within several minutes, alternating direction from south-to-north and north-to-south. Each scan consisted of eight 128x256 binned subframes. Each half-hour set alternated between slower scans with longer frame exposure times and faster scans with shorter frame durations.   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.  HRII_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 are related to this one and may be useful for research:  DIF-M-HRII-3/4-EPOXI-MARS-V1.0 - Calibrated HRII Mars observations  DIF-CAL-HRII-2-EPOXI-CALIBRATIONS-V1.0 - Raw HRII dark frames that bracket each set of Mars observations in 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 images of Mars at 350, 450, 550, 650, 750, 850, and 950 nm, covering the same observing period as this data set  DIF-M-MRI-2-EPOXI-MARS-V1.0 DIF-M-MRI-3/4-EPOXI-MARS-V1.0 - Raw and calibrated MRI visible CCD images of Mars at 750 nm, serving as context for the IR spectra and covering the 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 (wavelength and spatial/along-slit) FITS spectral 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 spectral image is stored as FITS. The primary data unit contains the two-dimensional spectral image, with the fastest varying axis corresponding to increasing wavelengths from about 1.05 to 4.8 microns and the slowest varying axis corresponding to the spatial or along-slit dimension. The primary array 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 HIyymmddhh_eeeeeee_nnn.LBL or FIT where 'HI' identifies the HRII 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 can be commanded for one exposure ID. Spectral scans often had 32 or more frames for one specific exposure. 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 1000002, the first FITS file name would be HI09112011_1000002_001.FIT and the last would be HI09112011_1000002_008.FIT.   Image Compression ----------------- Although raw data numbers for HRII 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 spectra 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 or wavelength) increasing to the right in the display window and the slowest-varying axis (lines or spatial/along-slit) 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.   Spectral Scans -------------- Each IR scan across the Mars consists of multiple frames within one exposure ID (OBSERVATION_ID in the data labels). To work with these spectral scans, it is recommended that all frames for one exposure ID be stacked into a three-dimensional cube. Then, a spatial-spatial map can be produced for a specific wavelength by selecting the appropriate spectral column from the image cube. Spectral wavelengths are provided by the second FITS extension, the spectral registration (wavelength) map.   IR Slit Location ---------------- For a comparison of the relative locations of the IR slit with respect to the fields of view of the Medium Resolution Instrument Visible CCD (MRI) and the High Resolution Instrument Visible CCD (HRIV), see the relative boresight alignments section of the Deep Impact instrument calibration document.   Timing for Spectra ------------------ It is important to note that the readout order of the IR detector affects the timing of the spectra. When a HRII spectral image is displayed using the true-sky convention, the wavelength increases horizontally to the right and the spatial or along-slit direction is vertical. In this orientation, the IR detector was read out from the left and right edges and toward the center and starting with the first row at the bottom and ending with the last row at the top of the display. Since the detector is reset and read out on a pixel-by-pixel basis, the read out order affects the time at which each pixel is exposed, although each pixel has the same exposure duration. Additionally, the end of the spectrometer slit that always points roughly towards the sun is the first line to be readout and the last line to be read out is furthest from the sun, assuming the spacecraft is in its usual orientation with the solar pointing roughly toward the sun. For more information about the timing of the spectra, see the IR focal plane and quadrant nomenclature sections of the Deep Impact instrument calibration document.   Parameters :  Data Units ---------- Raw spectral image data have units of raw data numbers.   Imaging Modes ------------- One image mode was used for all HRII Mars spectra:  X-Size Y-Size Bin Mode Name (pix) (pix) Type Comments ---- ------ ------ ----- ----- --------------------------------- 2 BINSF1 512 126 2x2 Binned sub-frame  In the table above, X-Size is the spectral dimension and Y-Size is the spatial dimension. 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.   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.

Confidence Level Overview : The data files in this data set were reviewed internally by the EPOXI project.   Review : The PDS Small Bodies Node held a peer review for this data set on 29 September 2010. The reviewers certified this data set for scientific use and archiving on 29 September 2010.   Data Coverage and Quality : There are no unexpected gaps in this data set. All Mars observations received on the ground were processed and included in this data set.  Horizontal striping through some images indicates missing data. The image quality map extension identifies where pixels are missing. If the second most-significant bit of a pixel in the image quality map is turned on, then data for the corresponding image pixel is missing. For more information, refer to EPOXI SIS document.   Limitations :  Timing ------ The flyby spacecraft clock SPICE kernel (SCLK) used to compute UTC values in the data labels and FITS headers has known discontinuities of up to a second. If time and funding permit, the EPOXI project will provide more precise times after the mission ends.   HRI Telescope Focus ------------------- Images of stars acquired early during the Deep Impact mission in 2005 indicated the HRI telescope was out of focus. However, this focus problem does not significantly affect the HRII instrument. For more details, please see the instrument calibration paper by Klaasen, et al. (2008) [KLAASENETAL2006].   Displaying Images ----------------- Flight software writes an image header over the first 100 bytes of quadrant A. These image header pixels were included in the raw FITS images. Since the values in these pixels vary dramatically, it is recommended that the values of the MINIMUM and MAXIMUM keywords in the data label (or the MINPVAL and MAXPVAL in the FITS header) be used to scale an image for display because these values exclude the header bytes as well as the reference rows and columns located around the edge of the spectral image. For more information, see the quadrant nomenclature section of the Deep Impact instrument calibration document or the EPOXI SIS document.