Data Set Overview : This data set contains version 1.0 of calibrated, 1.05- to 4.8-micron spectra of Earth acquired by the High Resolution Infrared Spectrometer (HRII) during the EPOCh phase of the EPOXI mission. Three sets of observations were acquired on 18-19 March, 28-29 May, and 4-5 June 2008 to characterize Earth as an analog for extrasolar planets. Each observing period lasted approximately 24 hours, and spectra were acquired twice per hour. During the observing period in May, the Moon transited across Earth as seen from the spacecraft.  At every half hour of each observing period, the spacecraft slewed across the Earth 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.  Additional Earth observations are being planned for the mission because two observing periods that were scheduled from late March through early May 2008 were canceled due to a telecommunications anomaly on board the spacecraft. These data will be added to a future version of this data set.   Required Reading --------------- The following documents are essential for the understanding and interpretation of this data set. Please note the most recent version of these documents, including other formats such as ASCII text, can be found in the Deep Impact and EPOXI documentation data set, DI-C-HRII-HRIV-MRI-ITS-6-DOC-SET-V2.0.  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_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 - This document provides pointing and sequencing information for the EPOCh Earth observations in 2008, 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.  HRII_3_4_EPOXI_EARTH.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.  Publications of the scientific results from the Earth observations in this data set include Cowan, et al. (2009) [COWANETAL2009] and Livengood, et al. (2009) [LIVENGOODETAL2009].   Related Data Sets ----------------- The following PDS data sets are related to this one and may be useful for research:  DIF-E-HRII-2-EPOXI-EARTH-V1.0 - Raw HRII Earth observations  DIF-CAL-HRII-2-EPOXI-CALIBRATIONS-V1.0 - Raw HRII dark frames that bracket each set of Earth observations in this data set  DIF-E-HRIV-2-EPOXI-EARTH-V1.0 DIF-E-HRIV-3/4-EPOXI-EARTH-V1.0 - Raw and calibrated HRIV visible CCD Earth observations at 350, 450, 550, 650, 750, 850, and 950 nm, covering the same three observing periods as this data set  DIF-E-MRI-2-EPOXI-EARTH-V1.0 DIF-E-MRI-3/4-EPOXI-EARTH-V1.0 - Raw and calibrated MRI visible CCD context images of Earth at 750 nm, covering only the March 2008 observing period.  DI-C-HRII-HRIV-MRI-ITS-6-DOC-SET-V2.0 - Deep Impact and EPOXI documentation set  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   Processing : The calibrated two-dimensional (wavelength and spatial/along-slit) FITS spectral images and PDS labels in this data set were generated by the Deep Impact/EPOXI calibration pipeline, maintained by the project's Science Data Center (SDC) at Cornell University. For HRII spectra, 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.  - 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.  The calibration pipeline performed the following processes on the raw HRII FITS data to produce the RADREV and RAD products found in this data set:  - Calibration of temperatures and voltages in the FITS header - Decompression of compressed images (Earth spectra were not compressed) - Linearization of raw data numbers - Subtraction of dark noise - Removal of electronic cross-talk (a unit correction) - 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.  ** A flat-field correction was not applied because the process in this version of the calibration pipeline is not adequate.  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 FITS image extensions for a spectral registration (wavelength) map, a spectral resolution (bandwidth) map, and a signal-to-noise ratio map. The calibration steps and files applied to each raw image are listed in the PROCESSING_HISTORY_TEXT keyword in the PDS data label. For a detailed discussion of the calibration pipeline and the resulting data, see the Deep Impact instrument calibration document and the EPOXI SIS document.  The calibrated spectra in this data set were the best available data as of February 2009. There are known deficiencies for spectra from the Deep Impact mission that are also relevant to the EPOXI Earth spectra in this data set. The HRII calibration limitations document describes these limitations.   Data :  FITS Images and PDS Labels -------------------------- Each calibrated 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 image is followed by four image extensions that are two-dimensional pixel-by-pixel maps providing additional information about the spectral 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 the spectral registration or wavelength for each pixel in the primary image. This extension is required because the wavelength for each pixel changes as the temperature of the instrument increased or decreased.  - The third extension provides the spectral bandwidth for each pixel in the primary image. This extension is required because the bandwidth for each pixel changes as the temperature of the instrument increased or decreased.  - The fourth extension provides a signal-to-noise ratio for each pixel in the primary image.  For more information about the FITS primary image and the extensions, refer to the Deep Impact instrument calibration document or the EPOXI SIS 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_rr.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), 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 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 32 frames were commanded for a scan with an exposure ID of 1000001, the first FITS file name would be HI08060416_1000001_001_RR.FIT and the last would be HI08060416_1000001_032_RR.FIT.   Image Compression ----------------- All data products in this data set are uncompressed. If the associated raw data products was compressed on board the flyby spacecraft (and thus received on the ground and archived as compressed) then the calibration pipeline uses one of four 8-bit lookup tables to decompress the raw image. However, the Earth spectra acquired acquired during the time period covered by this data set were never compressed. 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 Earth 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 ---------- Calibrated RADREV and RAD spectral images have units of radiance, W/(m**2 steradian micron).   Imaging Modes ------------- One HRII image mode was used for all Earth 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 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 that were calculated for the time when the light arrived at the target and the earth-observer-to-target values that were calculated for the time when the light left the target.  The flyby spacecraft clock SPICE kernels (SCLK) used to convert to UTC and to calculate geometry-related parameters for this data set have a known accuracy of no better than 0.5 seconds. However as this data set was being produced, the mission operations team figured out how to correct raw clock correlation data for the flyby spacecraft to allow timing fits that are accurate to at least the sub-second level. The project plans to generate a complete, corrected set of correlations since launch. This will ultimately result in a future version of a SCLK kernel that will retroactively change correlation for **all** Deep Impact and EPOXI data. When this kernel is available, it will be added to the SPICE data sets for the two missions and posted on the NAIF/SPICE web site at http://naif.jpl.nasa.gov/naif/.   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. NAIF used these kernels to produce the EPOXI SPICE data set, DIF-C/E/X-SPICE-6-V1.0.   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 : This data set is archived at the PDS Small Bodies Node (SBN) and the Multi-Mission Archive at STScI (MAST). It passed a peer review held by SBN on 23 July 2009; MAST personnel participated.   Data Coverage and Quality : There are no unexpected gaps in this data set. All Earth 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 :  Predicted observational geometry -------------------------------- Some data products for the Earth observation on 28-29 May (2008/149-150) have geometry values based on predicted (estimated) pointing C-kernels found in the EPOXI SPICE archive. Memory limitations on board the spacecraft caused some attitude information to be overwritten, and thus reconstructed (final and accurate) pointing data for part of this observing period were not generated nor available to the data pipeline . However the EPOCh team provided a file of geometry from JPL Horizons that they used for analysis of the May Earth data. See EPOCH_EARTH_GEOM_2008MAY.ASC located in the DOCUMENT/ directory of this data set.   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 are included in the calibrated 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.