Data Set Information
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| DATA_SET_NAME |
EPOXI EARTH OBS - HRII CALIBRATED SPECTRA V2.0
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| DATA_SET_ID |
DIF-E-HRII-3/4-EPOXI-EARTH-V2.0
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| NSSDC_DATA_SET_ID |
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| DATA_SET_TERSE_DESCRIPTION |
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| DATA_SET_DESCRIPTION |
Data Set Overview : This dataset contains calibrated, 1.05- to 4.8-micron spectra of Earth acquired by the High Resolution Infrared Spectrometer (HRII) during the EPOCh and Cruise 2 phases of the EPOXI mission. Five sets of observations were acquired on 18-19 March, 28-29 May and 04-05 June 2008 and on 27-28 March and 04-05 October 2009 to characterize Earth as an analog for extrasolar planets. Each observing period lasted approximately 24 hours; every two hours spectra were acquired twice within a twenty-minute interval. During the observing period in May 2008, the Moon transited across Earth as seen from the spacecraft. HRII spectra were not acquired during the first attempt of an Earth south polar observation on 27-28 September 2009 because fault protection turned that instrument off; the full sequence was successfully rerun on 04-05 October 2009. Version 2 corrects an error in the IR absolute calibration that previously inflated all spectra by a factor of 2. It also includes the application of an improved flat field 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. Every two hours the spacecraft was slewed across the disk of Earth six times while the IR spectrometer recorded data. The scans were performed in sets of three as the scan direction was alternated from south-to-north, north-to-south, then south-to-north. Each scan (exposure ID) consisted of eight 512x128 binned subframes. Each set of three scans alternated between slower scans with longer frame exposure times and faster scans with shorter frame durations. Each set of three scans took about five minutes to acquire. The position of the IR slit with respect to the disk of Earth at the start of each scan and the scan rate and direction are provided in EPOCH_EARTH_SEQ_2008.PDF and, EPOCH_EARTH_SEQ_2009.PDF located in the document directory. Required Reading --------------- The documents listed below are essential for the understanding and interpretation of this dataset. Although a copy of each document is provided in the DOCUMENT directory of this dataset, 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 EPOXI datasets, 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 dataset 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. HRII_3_4_EPOXI_EARTH.TAB - This ASCII table provides image parameters such as the mid-obs Julian date, exposure time, image mode, mission activity type, and description or purpose for each observation (i.e., data product) in this dataset. This file is very useful for determining which data files to work with. Publications of the scientific results from the Earth observations in this dataset include Cowan, et al. (2009) [COWANETAL2009] and Livengood, et al. (2009) [LIVENGOODETAL2009]. Related Data Sets ----------------- The following PDS datasets 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 dataset 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 dataset DIF-E-MRI-2-EPOXI-EARTH-V1.0 DIF-E-MRI-3/4-EPOXI-EARTH-V2.0 - Raw and calibrated MRI visible CCD context images of Earth at 750 nm, serving as context for the IR spectra and covering the Mar 2008, Mar 2009, Sep 2009, and Oct 2009 observing periods 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 (wavelength and spatial/along-slit) FITS spectral images and PDS labels in this dataset 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 dataset: - Calibration of temperatures and voltages in the FITS header - Decompression of compressed images (Earth spectra were not compressed) - Per-quadrant linearization of raw data numbers - Subtraction of dark noise - Removal of electronic cross-talk (a unit correction) - Division by a flat field, derived for per-quadrant linearization - Assignment of spectral registration and bandwidth for each pixel (using OPTBENT from FITS headers) - Conversion of data numbers to units of radiance for an absolute, radiometric calibration that is reversible (RADREV) and that was derived for per-quadrant linearization - 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. - Set non-image pixels at the left, right, and bottom edges to zero in the RADREV and RAD products. The 'real data' window of an image is given by CALWINDW in the FITS header. If edge pixels need to be analyzed, the original DN values can be found in the raw products located in the PDS dataset, DIF-E-HRII-2-EPOXI-EARTH-V1.0. As part of the calibration process, the pipeline updated the per-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 derived for per-pixel linearity (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, which are briefly described in the next section. 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 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 consisting of eight, single-bit flags to describe the quality of each pixel in the primary image. The PDS data label defines the purpose of each single-bit flag. - 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. 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 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 dataset are uncompressed. Specifically all raw Earth spectral images were never compressed. 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 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 FITS image data from the three science instruments, see the quadrant nomenclature section of the the EPOXI SIS document. Spectral Scans -------------- Each IR scan across Earth consists of eight frames for 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 instrument alignment section of the EPOXI SIS document or Klaasen, et al. (2013) [KLAASENETAL2011]. There are no visible CCD context images provided in this dataset to aid in orienting the IR slit location with the nucleus during a particular observation. In many cases, nearly simultaneous MRI frames, located in the dataset DIF-E-MRI-3/4-EPOXI-EARTH-V2.0, were acquired during the IR scans and may provide field of view context for the slit location. 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 -- except for the ALTFF mode that has different read and reset causing the effective exposure time to vary with line number, i.e., along the slit in the spatial direction. 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 panels pointing roughly toward the sun. For more information about the timing of the spectra, see the zero exposure background section of the EPOXI instrument calibration paper by Klaasen, et al. (2013) [KLAASENETAL2011]. Parameters : Data Units ---------- Calibrated RADREV and RAD spectral images have units of radiance, W/(m**2 steradian micron). Imaging Modes ------------- One mode was used for all images in this dataset: 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 along the slit. For more information see Hampton, et al. (2005) [HAMPTONETAL2005], Klaasen, et al. (2008) [KLAASENETAL2006] and Klaasen, et al. (2013) [KLAASENETAL2011]. 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. 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 dataset 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 dataset.
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| DATA_SET_RELEASE_DATE |
2013-08-03T00:00:00.000Z
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| START_TIME |
2008-03-18T06:21:12.137Z
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| STOP_TIME |
2009-10-05T09:59:10.674Z
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| MISSION_NAME |
EPOXI
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| MISSION_START_DATE |
2007-09-26T12:00:00.000Z
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| MISSION_STOP_DATE |
2013-09-20T12:00:00.000Z
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| TARGET_NAME |
EARTH
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| TARGET_TYPE |
PLANET
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| INSTRUMENT_HOST_ID |
DIF
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| INSTRUMENT_NAME |
DEEP IMPACT HIGH RESOLUTION INSTRUMENT - IR SPECTROMETER
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| INSTRUMENT_ID |
HRII
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| INSTRUMENT_TYPE |
INFRARED SPECTROMETER
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| NODE_NAME |
Small Bodies
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| ARCHIVE_STATUS |
LOCALLY_ARCHIVED
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| CONFIDENCE_LEVEL_NOTE |
Confidence Level Overview : The data files in this dataset were reviewed internally by the EPOXI project. Review : This dataset was peer reviewed and certified for scientific use on 21 March 2014. Data Coverage and Quality : There are no unexpected gaps in this dataset. All Earth observations received on the ground were processed and included in this dataset. 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 ------ An improved operations spacecraft clock SPICE kernel, DIF_SCLKSCET.00119.TSC, was used to convert to UTC and to calculate geometry-related parameters for this dataset. Therefore observation times for these calibrated images are improved and differ at the sub-second level when compared to the archived raw images. The EPOXI project plans to generate a complete and highly accurate set of UTC 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 datasets for the two missions and posted on the NAIF/SPICE web site at http://naif.jpl.nasa.gov/naif/. Predicted/Observational Geometry --------------------------------- Some data products for the Earth observation in May 2008 and October 2009 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 information for part of this observing period was not generated nor available to the data pipeline. However the EPOCh team provided a file of the observational geometry parameters they computed and used for their analysis. See EPOCH_EARTH_GEOM_2008MAY.ASC and EPOCH_EARTH_GEOM_2009OCT.ASC located in the DOCUMENT/ directory of this dataset. 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 EPOXI:MINIMUM and EPOXI: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 at the edges of the image. For more information, see the quadrant nomenclature section of the EPOXI SIS document.
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| CITATION_DESCRIPTION |
McLaughlin, S.A., B. Carcich, D. Deming, T. Livengood, T. Hewagama, K.P. Klaasen, and D.D. Wellnitz, EPOXI EARTH OBS - HRII CALIBRATED SPECTRA V2.0, DIF-E-HRII-3/4-EPOXI-EARTH-V2.0, NASA Planetary Data System, 2014.
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| ABSTRACT_TEXT |
This dataset contains calibrated, 1.05- to 4.8-micron spectra of Earth acquired by the High Resolution Infrared Spectrometer (HRII) during the EPOCh and Cruise 2 phases of the EPOXI mission. Five sets of observations were acquired on 18-19 March, 28-29 May and 04-05 June 2008 and on 27-28 March and 04-05 October 2009 to characterize Earth as an analog for extrasolar planets. Each observing period lasted approximately 24 hours, and spectra were acquired twice every 2 hours. During the observing period in May 2008, the Moon transited across Earth as seen from the spacecraft. HRII spectra were not acquired during the first attempt of an Earth south polar observation on 27-28 September 2009 because fault protection turned that instrument off; the full sequence was successfully rerun on 04-05 October 2009. Version 2 corrects an error in the IR absolute calibration that previously inflated all spectra by a factor of 2.
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| PRODUCER_FULL_NAME |
STEPHANIE MCLAUGHLIN
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| SEARCH/ACCESS DATA |
SBN Comet Website
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