Data Set Information
DATA_SET_NAME DEEP IMPACT 9P/TEMPEL ENCOUNTER - REDUCED ITS NAV IMGS V1.0
DATA_SET_ID DII-C-ITS-3-NAV-9P-ENCOUNTER-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : This data set contains calibrated images of comet 9P/Tempel 1 acquired by the Deep Impact Impactor Targeting Sensor Visible CCD (ITS) during the encounter phase of the mission. These observations were used for optical and autonomous navigation (NAV) of the impactor spacecraft as well as for scientific investigations. These data were collected on 3-4 July 2005. Software on board the impactor spacecraft used the optical navigation (OpNav) and autonomous navigation (AutoNav) images to compute the brightness centroid of the target body for trajectory corrections. Optical navigation was used until two hours before impact when the AutoNav system took control of the impactor spacecraft. For more information about the AutoNav system, see Mastrodemos, et. al (2005) [MASTRODEMOSETAL2005]. A NAV observation consisted of one or more packets of data, each containing an 80-byte header plus a rectangle of image data called a ''snip'', cropped from a full-frame image. Pixels outside the snips were not returned. The Deep Impact Science Data Center (SDC) at Cornell University, used the packets for one observation to reconstruct a raw, full-frame image of 1008 by 1008 pixels with one common header. The data pipeline flagged pixels outside the snips as missing but did not capture the locations of the snips within a frame. The raw, reconstructed images were then input to the calibration pipeline at the SDC. For more information about the calibrated NAV images, see the processing section below. Reduced NAV images were grouped into daily directories by mid- observation date. A list of the NAV images in the data set is provided here: Exposure IDs OBS Date DOY Minimum Maximum Observation Type ---------- --- ------- ------- ------------------------------------ 2005-07-03 184 1000000 1000016 Comet imaging 9000000 9000123 Comet imaging 2005-07-04 185 1000017 1000019 Comet imaging 9000129 9000135 Comet imaging 9000143 9000515 Comet imaging Essential Reading ----------------- The following documents, located on the Deep Impact Documentation volume, DIDOC_0001, are essential for the understanding and interpretation of this data set: NAV_IMAGES_REPORT.* : Description of how raw and reduced NAV FITS images were created for and processed by the Deep Impact science data pipeline NAV_ITS_REDUCED_ENCOUNTER.* : Science-related image indices for this data set NAV_ITS_FILE_NAMES_RAW2CAL.* : Cross-reference of raw and reduced NAV file names CALIBRATION_DOC.* : Instrument calibration by Klaasen, et al. (2006) [KLAASENETAL2006] INSTRUMENTS_HAMPTON.* : Instrument paper by Hampton, et al. (2005) [HAMPTONETAL2005] AUTO_NAVIGATION_MASTRODEMOS.* : Auto-navigation paper by Mastrodemos, et. al (2005) [MASTRODEMOSETAL2005] MISSION_OVERVIEW_AHEARN.* : Mission overview by A'Hearn, et al. (2005) [AHEARNETAL2005B] SCLK_CORRELATION.* : Discussion of the discrepancy between the spacecraft clocks and UTC AICD_FLIGHT_HRIV_MRI_ITS.* : Description of the data set and definitions of label keywords Related Data Sets ----------------- The following PDS data sets are related to this one: DII-CAL-ITS-2-NAV-9P-CRUISE-V1.0 : Raw ITS NAV cruise data DII-C-ITS-3-NAV-9P-ENCOUNTER-V1.0 : Raw ITS NAV encounter data DI-C-SPICE-6-V1.0 : SPICE kernels The related Deep Impact science data sets are: DII-CAL-ITS-2-9P-CRUISE-V1.0 : Raw ITS cruise data DII-C-ITS-2-9P-ENCOUNTER-V1.0 : Raw ITS encounter data DII-C-ITS-3/4-9P-ENCOUNTER-V1.0 : Calibrated ITS encounter data Processing : The reduced, two-dimensional FITS images in this data set were generated by the Deep Impact calibration pipeline, maintained by the project's Science Data Center (SDC) at Cornell University. The NAV images report, listed above in the recommended reading section, discusses how the NAV snips were processed into raw images and describes the steps performed by the calibration pipeline to reduced the raw data. A summary is provided here. NAV images were typically acquired during sequences designed to gather science data. The major difference between a science and NAV image was that a NAV observation was made of one or more packets of data, each containing an 80-byte header plus a rectangle of image data called a ''snip''. Because the snips were cropped from a full-frame image, not all pixels were returned in many cases. However, some images were returned in full as a single snip of 1008 by 1008 pixels. Because a raw NAV observation was received as one or more snips, the SDC reconstructed a full frame of 1008 by 1008 pixels from the snips and stored the results as raw a FITS file. These minimally processed FITS files were archived as the raw NAV data sets in the PDS. Since the raw NAV data excluded the serial- and parallel-overclock pixels around the edges of the array, the SDC pre-processed the raw NAV FITS images to include this information to make the data look enough like a 1024x1024-pixel, full-frame science image so that the existing calibration pipeline could be used. The pipeline performed the following reduction steps to produce the reduced FITS images in this data set: - Calibration of temperatures in the FITS header - Linearization of data number values - Correction for bias (using pre-determined values from the BIASVAL1, BIASVAL2, BIASVAL3, and BIASVAL4 entries in the PROCESSING_HISTORY_TEXT keyword in the PDS labels) - Subtraction of a dark frame - Application of a flat field to normalize the data - Conversion of data numbers to units of radiance for an absolute, radiometric calibration The following calibration steps were disabled (however, calibration files associated with some of these steps, such tables for removing cross-talk, were included in the calibration subdirectory for completeness): - Decompression (NAV data were never compressed) - Calibration of temperatures in the FITS header - Removal of electronic cross-talk and smear - Normalization of quadrant gains (included in flat fields) - Correction for uneven bit weighting due to analog-to-digital (ADC) conversion (a unit correction) - Gap filling - Removal of random gaussian noise - Despiking - Deconvolution - Geometric calibration The resulting data were provided in physical units of radiance, Watts/(meter**2 steradian micron). These data, designated by the mnemonic ''RADREV'', were not cleaned and are considered reversible because the calibration steps can be removed to get back to the original, raw data numbers. During the calibration process, the pipeline updated the pixel-by-pixel image quality map, the first FITS extension, so the following types of pixels could be identified: - 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 - Pixels considered bad as indicated by bad pixel maps The pipeline also created a second FITS image extension for a pixel-by-pixel signal-to-noise ratio map. The calibration steps and files used to reduce each raw image are listed in the PROCESSING_HISTORY_TEXT keyword in the PDS data label for that image. For a detailed discussion of the calibration pipeline and the resulting data, see the instrument calibration document by Klaasen, et al. (2006) [KLAASENETAL2006]. Applied Coherent Technology Corporation in Herndon, VA, produced the PDS data labels by extracting parameters from the FITS headers. Data : File Naming Convention ---------------------- The naming convention for the data labels and FITS files was Ixcccccccccc_eeeeeee_nnn_RR.LBL or FIT, where: I : ITS instrument x : Image usage (A for AutoNav or O for OpNav) cccccccccc : Spacecraft clock count at the image mid-point eeeeeee : Exposure ID, same as for science data; image number within an exposure ID was always 1 of 1 yyyy : Ground-received time (GRT) year ddd : GRT day of year hhmmss : GRT hours, minutes, and seconds nnn : Sequentially increasing image number within an exposure ID (always 1 of 1 for NAV data) It is important to note that a different file naming convention was used for the raw NAV images. A cross-reference of the raw and calibrated NAV file names is included on the documentation volume. FITS CCD Images --------------- The two-dimensional, CCD images in this data set are in FITS format. The primary data array contains the image, followed by two image extensions that are pixel-by-pixel maps which provide additional information about the primary 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. Each image FITS file is accompanied by a detached PDS label. For more information about the FITS primary image and extensions, refer to the instrument calibration document. True-Sky ''As Seen By Observer'' Display ---------------------------------------- A true-sky 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 increasing to the top. This convention is also defined in the data labels: SAMPLE_DISPLAY_DIRECTION : 'RIGHT' LINE_DISPLAY_DIRECTION : 'UP' The direction to Celestial North and Ecliptic North, measured clockwise from the top of the displayed image, is provided in PDS labels by CELESTIAL_NORTH_CLOCK_ANGLE and SOLAR_NORTH_POLE_CLOCK_ANGLE, both of which assume the correct display defined by SAMPLE_DISPLAY_DIRECTION and LINE_DISPLAY_DIRECTION. Using this convention for Tempel 1 approach images, ecliptic East is toward the left, ecliptic North is up, and the Sun is to the right. This was also the convention used when displaying science images of Tempel 1 in published papers. For a comparison of the orientation of ITS flight images with those from ground-based calibrations as well as those from the High and Medium Resolution Instrument CCDs (HRIV and MRI, respectively), see the quadrant nomenclature section of the 'Deep Impact Instrument Calibration' document. Parameters : Data Units ---------- Reduced RADREV data are in units of radiance, W/(m**2 steradian micron). The data are reversible and are not cleaned. Imaging Modes ------------- The unbinned, full-frame, instrument mode 1 was always used for NAV images. For descriptions of the imaging modes, please see the Deep Impact instrument paper by Hampton, et al. (2005) [HAMPTONETAL2005]. During pre-processing, the SDC added overclock rows and columns around the edges of the raw NAV FITS images so that the data could be processed by the calibration pipeline used for the science images. Pixels in the overclock areas were excluded from the calculation of the values for MINIMUM, MAXIMUM, MEDIAN, and STANDARD_DEVIATION in the data labels. Time-Related Keywords --------------------- All time-related keywords in the data labels, except EARTH_RECEIVED_TIME, are based on the clock on board the spacecraft. EARTH_RECEIVED_TIME provides the UTC when an Earth-based observer should be able to see an event recorded by the instrument. Although the time to impact was not calculated for the NAV data, the estimated time of impact at the impactor spacecraft was UTC 05:44:34.200 on 4 Jul 2005. This is based on the conclusions presented in the spacecraft clock correlation document. Geometry-Related Keywords ------------------------- The SOLAR_NORTH_POLE_CLOCK_ANGLE in the data labels specified the the direction of ecliptic north as projected onto the image plane. It is measured from the 'upward' direction, clockwise to the direction toward ecliptic north when the image is displayed as defined by the SAMPLE_DISPLAY_DIRECTION and LINE_DISPLAY_DIRECTION keywords. The SDC pipeline was not able to automatically determine the proper geometric information for the target of choice in many cases. When these parameters could not be computed, the corresponding keywords in the PDS data labels were set to a value of unknown (UNK). Geometry-related keywords for most calibration targets were set to UNK. Geometric parameters provided in the data labels were computed at the epoch specified by MID_IMAGE_TIME, except for the target-to-sun and earth-observer-to-target parameters. Target-to-sun values were calculated for the time when the light left the sun while earth-observer-to-target were calculated for the time when the light left the target. Geometry-related parameters in the PDS data labels are uncertain at a level of a few seconds because of a known 2-second discrepancy between the clocks on board the flyby and impactor spacecraft and between in-situ data and ground-based observations. After a detailed analysis of the timing problem in early 2006, improved self-consistent SPICE kernels were generated by the Deep Impact project to correlate the spacecraft clocks; there is still a 1-2 second uncertainty between the in-situ data and the ground- based observations and an uncertainty of about one half of a second between the clocks on the flyby and impactor spacecraft. These improved kernels were included in the DI SPICE data set and were used to calculate the geometric parameters in the PDS data labels. For more information about this discrepancy, please see the spacecraft clock correlation report provided on the DI documentation volume, DIDOC_0001. The SPICE kernels used to calculated the geometric parameters are provided by the SPICE_FILE_NAME keyword in the PDS data labels. The kernels were listed in the order they were loaded into memory for processing. Ancillary Data : Geometric parameters included in the data labels were computed using the DI SPICE data set archived in the PDS. Coordinate System : Earth Mean Equator and Vernal Equinox of J2000 (EME J2000) was the inertial reference system used to specify observational geometry parameters in the data labels.
DATA_SET_RELEASE_DATE 2006-09-29T00:00:00.000Z
START_TIME 2005-07-03T06:44:32.076Z
STOP_TIME 2005-07-04T05:14:32.550Z
MISSION_NAME DEEP IMPACT
MISSION_START_DATE 2005-01-12T12:00:00.000Z
MISSION_STOP_DATE 2005-07-13T12:00:00.000Z
TARGET_NAME 9P/TEMPEL 1 (1867 G1)
TARGET_TYPE COMET
INSTRUMENT_HOST_ID DII
INSTRUMENT_NAME DEEP IMPACT IMPACTOR TARGETING SENSOR - VISIBLE CCD
INSTRUMENT_ID ITS
INSTRUMENT_TYPE CCD CAMERA
NODE_NAME Small Bodies
ARCHIVE_STATUS ARCHIVED
CONFIDENCE_LEVEL_NOTE Confidence Level Overview : As noted above, the geometry-related parameters in the PDS data labels are uncertain at a level of a few seconds because of a known 2-second discrepancy between the clocks on board the flyby and impactor spacecraft and between in-situ data and ground-based observations. For more information about this discrepancy, please see the spacecraft clock correlation document included on the Deep Impact documentation volume. The FITS files in this data set were reviewed internally by the Deep Impact project and were used by the science team for photometric analysis of 9P/Tempel 1. Review : This data set was peer-reviewed in November 2006 and was accepted for the PDS archive pending resolution of liens (completed in June 2007). Data Coverage and Quality : All expected data were received on the ground and are included in this data set. There are gaps in the exposure IDs in some daily data directories because NAV frames were interspersed with science frames. Limitations : 1/3 Pixel Gap ------------- There is a 1/3-pixel, horizontal gap for a clocking phase between the upper and lower halves of the CCD. It was inserted by the manufacturer to facilitate the simultaneous upward and downward reading of the upper and lower quadrants. The gap causes a 10 percent reduction in the sensitivity of the two central rows (i.e., one row immediately above the gap and one below it). Displaying Images ----------------- A log scale is recommended for displaying reduced NAV images. Use the values of the the MINIMUM and MAXIMUM keywords in the PDS data label (or the MINPVAL and MAXPVAL in the FITS header) to set the range. While the overclock rows and columns located around the edge of the image were not included in these values, the pixels outside the snips were.
CITATION_DESCRIPTION Carcich, B., A.S. Shaw, M. Desnoyer, S.A. McLaughlin, N. Mastrodemos, and K.P. Klaasen, DEEP IMPACT 9P/TEMPEL ENCOUNTER - REDUCED ITS NAV IMGS V1.0, DII-C-ITS-3-NAV-9P-ENCOUNTER-V1.0, NASA Planetary Data System, 2006.
ABSTRACT_TEXT This data set contains calibrated images of comet 9P/Tempel 1 acquired by the Deep Impact Impactor Targeting Sensor Visible CCD during the encounter phase of the mission. These observations were used for optical and autonomous navigation (NAV) of the impactor spacecraft as well as for scientific investigations. These data were collected on 3-4 July 2005.
PRODUCER_FULL_NAME STEPHANIE MCLAUGHLIN
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