NSSDCA ID: PSSB-00597
Availability: Archived at NSSDC, accessible from elsewhere
This description was generated automatically using input from the Planetary Data System.
This dataset contains calibrated, 1.05- to 4.8-micron spectral images of the Moon acquired the High Resolution Infrared Spectrometer (HRII) from 29 December 2007 through 18 December 2009 during several in-flight instrument calibrations for the EPOXI mission. These data were used by Sunshine, et al. (2009) [SUNSHINEETAL2009] in 'Temporal and Spatial Variability of Lunar Hydration As Observed by the Deep Impact Spacecraft'. The following list summarizes the lunar calibrations in this dataset. Each exposure ID represents one set of spectral images that were taken as the Deep Impact flyby spacecraft scanned across the lunar disk. Descriptive text for each activity is included below. -----------------------------------------------------------------------Phase and Exposure ID Calibration Activity Obs Date/DOY Target Start Stop ---------------------------- -------------- -------- ------- ------Cruise 1 Lunar Calibration 2007-12-29/363 Moon 1000005 1070000 Cruise 2 HRII Lunar Flats&Radiometry 2009-06-01/152 Moon 1000000 1000000 2009-06-02/153 Moon 1000000 1000076 HRII Lunar Antisat Fltr&Rad 2009-06-09/160 Moon 1000000 1000519 HRII Lunar Flats/Rad Cal#1 2009-12-05/339 Moon 1000000 1000076 HRII Lunar Flats/Rad Cal#2 2009-12-12/346 Moon 1000000 1000076 HRII Lunar S.Pole Rad 2009-12-18/352 Moon 1000000 1000002 -----------------------------------------------------------------------Lunar Calibration: On 29 December 2007 as the spacecraft approached Earth, the three science instruments used the Moon as a target to acquire data for recalibration purposes. The sequence included along- and cross-slit HRII scans of the moon for flat fields and characterization of the HRII anti-saturation filter. (Please note the flat-field data were mostly saturated at long wavelengths). Due to a minor error in the lunar calibration sequence, a series of HRII dark frames were not recorded. A retest to acquire the missing HRII darks was scheduled for 16-17 January 2008. HRII Lunar Flats and Radiometry: On 1-2 June 2009, the HRII spectrometer acquired a series of east/west scans of the moon along the IR slit for flats. These data were the best obtained to date for the purpose of generating flat fields for the IR spectrometer. Also three cross-slit north/south scans of the moon were acquired for lunar radiometry. Please note these data have poor signal-to-noise at short wavelengths. HRII Lunar Antisat Filter and Radiometry: On 9 June 2009, the HRII spectrometer imaged the moon using cross-slit north/south scans to better characterize the effects of the anti-saturation filter in the IR spectra. These data were also used for radiometry. HRII Lunar Flats/Radiometric Cal #1 and #2: On 05 and 12 December 2009 as the spacecraft approached Earth, the IR spectrometer made north/south cross-slit scans of the moon for radiometry and east/west scans along the slit for lunar flats and a radiometric calibration. Please note the flat-field data are very good. HRII Lunar South Pole Radiometry: On 18 December 2009, about 10 days before the distant flyby of Earth the IR spectrometer made north/south cross-slit scans of the lunar south pole for radiometric analysis. 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. HRII_3_4_EPOXI_LUNAR_CALS.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. EPOXI_LUNAR_CAL_SEQUENCES.PDF - The EPOXI Lunar Calibration Sequences document provides the imaging sequences for the observations in this dataset. It includes the direction, rate, and a description for each scan. Related Data Sets ----------------The following PDS datasets are related to this one and may be useful for research: DIF-CAL-HRII-2-EPOXI-CALIBRATIONS-V2.0 - Raw HRII in-flight calibrations from 2007 to 2011 DIF-CAL-MRI-2-EPOXI-CALIBRATIONS-V2.0 - Raw MRI in-flight calibrations from 2007 to 2011, including context images of the Moon acquired during the HRII spectral scans DIF-C/E/X-SPICE-6-V1.0 - EPOXI SPICE kernels DIF-CAL-HRII/HRIV/MRI-6-EPOXI-TEMPS-V3.0 - 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 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. The final version of the pipeline for HRII processing, dated January 2013, was used. Known limitations and deficiencies of the pipeline and the resulting data are discussed in the EPOXI Calibration Pipeline Summary document in this dataset and by Klaasen, et al. (2013) [KLAASENETAL2011]. 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, in the order listed, on the raw HRII FITS data to produce the RADREV and RAD products found in this data set (the process uses the image mode to select the appropriate set of calibration files): - Calibration of temperatures and voltages in the FITS header - Per-pixel linearization of raw data numbers - Subtraction of dark noise, derived using pixel-by-pixel linearization of either optimized mode-dependent master dark frames (the prisms/spectral imaging module and IR focal plane array temperatures, OPTBENT and IRFPAT in the FITS header, are used for scaling because dark modeling is required for these data) - Division by a flat field, derived from pixel-by-pixel linearization - Determine 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 from pixel-by-pixel 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-CAL-HRII-2-EPOXI-CALIBRATIONS-V2.0. 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 calibrated 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 8 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 1000005, the first FITS file name would be HI07122918_1000005_001_RR_FIT and the last would be HI07122918_1000005_008_RR_FIT. Image Compression ----------------All data products in this dataset are uncompressed. 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 HRII scan of the Moon 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 ---------------There are no visible CCD context images provided in this dataset to aid in orienting the IR slit location with the Moon during a particular observation, although context images are available in the raw MRI in-flight calibration image dataset, DIF-CAL-MRI-2-EPOXI-CALIBRATIONS-V2.0. Utilizing the infrared data scans themselves is currently the best way to determine the slit location on the Moon. The user can create a three-dimensional cube as described above then use the ~2.4-micron spatial-spatial map to determine where the slit was pointed during that particular scan. Geometry values, such as right ascension and declination, given in the data labels are for the instrument boresight and do not easily give positional information along the slit for tying a pixel to a specific point on the Moon. 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]. A brief discussion about how the calibration pipeline handles the ALTFF mode is included in the EPOXI Calibration Pipeline Summary document. Parameters ========== Data Units ---------The calibrated RADREV and RAD image data have units of radiance, W/(m**2 steradian micron). Imaging Modes ------------A summary of the imaging modes is provided here. For more information see Hampton, et al. (2005) [HAMPTONETAL2005], Klaasen, et al. (2008) [KLAASENETAL2006] and Klaasen, et al. (2013) [KLAASENETAL2011]. In the table below, X-Size is the spectral dimension and Y-Size is the spatial dimension along the slit. X-Size Y-Size Bin Mode Name (pix) (pix) Type Comments ---- ------ ------ ----- ----- -----------------------------------1 BINFF 512 256 2x2 Binned full frame 2 BINSF1 512 126 2x2 Binned sub-frame 3 BINSF2 512 64 2x2 Binned sub-frame 4 UBFF 1024 512 1x1 Unbinned full frame 5 ALTFF 512 256 2x2 Alternate mode 1 (min. exposure time is 1/2 of mode 1) 6 DIAG 1024 512 1x1 Diagnostic, one reset frame followed by a separate read frame such that odd IMAGE_NUMBERs are reset frames and even IMAGE_NUMBERs are read frames 7 MEMCK 1024 512 1x1 Memory Check Subframe modes are binned (2x2), reduce the spatial (LINE) extent of the image FOV, and have a shorter readout time which reduces the exposure time for bright objects and keeps the detector from saturating. 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 lunar 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. The kernels are archived in the EPOXI SPICE dataset, 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. 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.
These data are available on-line from the Planetary Data System (PDS) at:
http://pdssbn.astro.umd.edu/holdings/dif-l-hrii-3_4-epoxi-lunar-cals-v1.0/
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 |