Data Set Information
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| DATA_SET_NAME |
MRO CRISM LIMB DATA RECORD V1.0
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| DATA_SET_ID |
MRO-M-CRISM-6-LDR-V1.0
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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 volume contains portions of the CRISM Limb Data Record (LDR) Archive, a collection of multiband images from the Compact Reconnaissance Imaging Spectrometer for Mars on the Mars Reconnaissance Orbiter spacecraft. Images consist of information on observation conditions of IR and VNIR data cubes pointed at Mars' limb, mapped to the sensor space of non-map-projected data. The data are stored with PDS labels. This volume also contains an index file ('imgindx.tab') that tabulates the contents of the volume, ancillary data files, and documentation files. For more information on the contents and organization of the volume set refer to the aareadme.txt file located in the root directory of the data volumes. Parameters : CRISM observing scenarios are constructed using a set of key variables ('configurations') which include the following. All are selectable separately for the VNIR and IR detectors. Only a subset of the configurations represent 'scene' data, as indicated by the EDR keyword MRO:ACTIVITY_ID. Only scene data that are aimed at Mars' limb have corresponding LDRs. Only those configurations that affect an LDR are discussed below: Image source: Image data may be generated using digitized output from the detector, or using one of up to seven test patterns. Only data from the detector may have a corresponding LDR. Pixel binning: Pixels can be saved unbinned or binned 2x, 5x, or 10x in the spatial direction. No pixel binning in the spectral direction is supported. Data with any pixel binning configuration may have a corresponding LDR, but the nominal binning configuration for limb-pointed observations is 10x. Calibration lamps: 4095 levels are commandable in each of two lamps at each focal plane, and in two lamps in the integrating sphere. All lamps can be commanded open-loop, meaning that current is commanded directly. For the integrating sphere only, closed loop control is available at 4095 settings. For closed loop control, the setting refers to output from a photodiode viewing the interior of the integrating sphere; current is adjusted dynamically to attain the commanded photodiode output. Note: lamps reach maximum current at open- or closed-loop settings <4095. Only data for which the calibration lamps are off may have an accompanying LDR. Shutter position: Open, closed, or viewing the integrating sphere. The shutter is actually commandable directly to position 0 through 32. In software, open:3, sphere:17, closed:32. NOTE: during integration and testing, it was discovered that at positions <3 the hinge end of the shutter is directly illuminated and creates scattered light. Position 3 does not cause this effect, but the other end of the shutter slightly vignettes incoming light. Only data in which the shutter is open, and at position 3, may have an accompanying LDR. Pointing: CRISM has two basic gimbal pointing configurations and two basic superimposed scan patterns. Pointing can be (1) fixed (nadir-pointed in the primary science orbit) or (2) dynamic, tracking a target point relative to the surface of Mars and taking out ground track motion. A limb observation tracks a point near Mars' limb along the projection of the groundtrack, and superimposes a scan relative to that point. Processing : The CRISM data stream downlinked by the spacecraft unpacks into a succession of compressed image frames with binary headers containing housekeeping. In each image, one direction is spatial and one is spectral. There is one image for the VNIR focal plane and one image for the IR focal plane. The image from each focal plane has a header with 220 housekeeping items that contain full status of the instrument hardware, including data configuration, lamp and shutter status, gimbal position, a time stamp, and the target ID and macro within which the frame of data was taken. These parameters are stored as part of an Experiment Data Record (EDR), which consists of raw data, or a Targeted Reduced Data Record, or TRDR, the 'calibrated' equivalent of an EDR. The data in one EDR or TRDR represent a series of image frames acquired with a consistent instrument configuration (shutter position, frame rate, pixel binning, compression, exposure time, on/off status and setting of different lamps). Each frame has dimensions of detector columns (spatial samples) and detector rows (wavelengths, or bands). The multiple image frames are concatenated, and are formatted into a single multiple-band image (suffix *.IMG) in one file, plus a detached list file in which each record has housekeeping information specific to one frame of the multiple-band image (suffix *.TAB). The multiple- band image has dimensions of sample, line, and wavelength. The size of the multiple-band image varies according to the observation mode but is deterministic given the macro ID. A typical multiple-band image might have XX pixels in the sample (cross-track) dimension, YY pixels in the line (along-track) dimension, and ZZ pixels in the wavelength dimension, where: XX (samples) : 640/binning, where 640 is the number of columns read off the detector, and binning is 1, 2, 5, or 10; YY (lines) : the number of image frames with a consistent instrument configuration; and ZZ (bands) : the number of detector rows (wavelengths) whose read-out values are retained by the instrument. Once image data are assembled into EDRs and calibrated into TRDRs, DDRs are created for data pointed at the surface, and LDRs are created for data pointed at the limb. For DDRs version 0 represents values based on predicted pointing, and version 1 is based on actual, reconstructed pointing. For LDRs both version 0 and 1 are used but both are based on reconstructed pointing. Each of the planes of an LDR represents some value evaluated at or above the surface intercept of Mars shape model, or at or above the intercept with a surface parallel to the areoid. The following items, some represented in SPICE files or 'kernels,' affect the properties encoded in an LDR: Position of Mars: This is encoded in the planetary ephemeris kernel. Position of MRO: This is encoded in the spacecraft ephemeris kernel. Orientation of MRO: This is encoded in the spacecraft C kernel. Orientation of CRISM's gimbal in the MRO reference frame: This is encoded in the CRISM part of the MRO frames kernel. Orientation of CRISM's VNIR and IR fields of view relative to the gimbal. This also is encoded in the CRISM part of the MRO frames kernel. Position of CRISM's gimbal within its plane: This is encoded in a CRISM C kernel. CRISM's C kernel is derived from gimbal positions at the beginning, middle, and end of the integration of each line of an EDR or TRDR images file, which is given in the table of instrument housekeeping that accompanies every EDR and TRDR. Position of each spatial pixel in a CRISM image relative to the center of the field of view: This is encoded in the instrument kernel. Mars shape model and areoid: The shape model and areoid used to construct DDRs and LDRs is from the Mars Orbiter Laser altimeter, or MOLA, gridded at 128 pixels per degree [SMITHETAL1999]. CRISM has optical distortions such that each wavelength, or band, has a very slightly different surface projection onto Mars. Each band corresponds to a row on the VNIR or IR detector. To avoid ambiguity, a DDR or LDR represents the information corresponding to a reference detector row near 610 nm (row number 223) for the VNIR, or near 2300 nm (row number 257) for the IR. The relationship between different bands is included in the instrument kernel. The sequence of processing that creates a DDR or LDR is as follows. EDRs are assembled from raw data. TRDRs are created from the EDRs and Calibration Data Records, or CDRs, using a calibration algorithm discussed at length in an Appendix in the CRISM Data Products SIS. Gimbal positions are extracted from the EDR housekeeping and formatted as a gimbal C kernel. Using that and other SPICE kernels discussed above, intercepts on the MOLA shape model or at a tangent height above it, and intercepts at a tangent height above the areoid are calculated for each spatial pixel (sample at the reference detector row). The derived image bands include the following: 1. Latitude. Defined in one of two ways: (a) If the instrument boresight does not intercept the Martian areoid: Evaluated at the tangent point of the limb observation; the intercept with the areoid of a vector originating at the center of the planet, that is normal to the instrument boresight. (b) If the instrument boresight does intercept the Martian areoid: same definition as in the DDR. Evaluated at the intercept of the instrument boresight with the MOLA shape model. 2. Longitude (planetocentric, east positive). Defined in one of two ways: (a) If the instrument boresight does not intercept the Martian areoid: Evaluated at the tangent point of the limb observation; the intercept with the areoid of a vector originating at the center of the planet, that is normal to the instrument boresight. (b) If the instrument boresight does intercept the Martian areoid: same definition as in the DDR. Evaluated at the intercept of the instrument boresight with the MOLA shape model. 3. Incidence angle at the latitude and longitude described above. Defined in one of two ways: (a) If the instrument boresight does not intercept the Martian areoid: the angle between a vector originating at the center of the planet that is normal to the instrument boresight, and a vector from the center of the sun to the surface intercept of the first vector. (b) If the instrument boresight does intercept the Martian areoid: the angle the normal to the areoid at the latitude and longitude described above, and a vector from the latitude and longitude on the areoid to the center of the sun. 4. Emission angle at the latitude and longitude described above. Defined in one of two ways: (a) If the instrument boresight does not intercept the Martian areoid: the angle between a vector originating at the center of the planet that is normal to the instrument boresight, and the instrument boresight. By definition, 90 degrees. (b) If the instrument boresight does intercept the Martian areoid: the angle between the instrument boresight and the normal to the areoid at the latitude and longitude described above. 5. Phase angle at the latitude and longitude described above. The angle between the instrument boresight and a vector from the sun to Mars. 6. Altitude relative to the areoid. Defined in one of two ways: (a) If the instrument boresight does not intercept the Martian areoid: The length of a segment along a vector originating at the center of Mars that passes through the latitude and longitude described above. One end of the segment is the intercept of the vector with the areoid. The other end is the intercept of the vector with the instrument boresight. (b) If the instrument boresight does intercept the Martian areoid: zero 7. Altitude relative to the MOLA shape model. Defined in one of two ways: (a) If the instrument boresight does not intercept the Martian areoid: The length of a segment along a vector originating at the center of Mars that passes through the latitude and longitude described above. One end of the segment is the intercept of the vector with the MOLA shape. The other end is the intercept of the vector with the instrument boresight. (b) If the instrument boresight does intercept the Martian areoid: zero CRISM data products and described in greater detail in the Data Products Software Interface Specification and the Data Archive Software Interface Specification in the DOCUMENT directory. Data : There is only one data type associated with this volume, the Limb Data Records or LDRs. There are 15 layers in each LDR, all represented as 32-bit real numbers arranged in band-sequential format: 1. Solar incidence angle at the areoid, units degrees 2. Emission angle at the areoid, units degrees 3. Phase angle, units degrees 4. Planetocentric latitude at the tangent point of the line of sight, units degrees N 5. Longitude at the tangent point of the line of sight, units degrees E, 6. Solar incidence angle at a surface intercept relative to a MOLA shape model, units degrees 7. Emission angle at a surface intercept relative to a MOLA shape model, units degrees 8. Elevation at the tangent point of the line of sight, units meters relative to areoid 9. Elevation at the tangent point of the line of sight, units meters relative to the MOLA shape model 10. Local Solar Time, units hours 11. Ephemeris Time of observation, seconds past noon January 1, 2000 12. Sub-solar planetocentric latitude, units degrees N 13. Sub-solar longitude, units degrees E 14. Sub-spacecraft planetocentric latitude, units degrees N 15. Sub-spacecraft longitude, units degrees E Ancillary Data : Ancillary data are provided with this dataset: 1. SPICE kernels, used to contruct observational geometry, are available in the GEOMETRY directory. See GEOMINFO.TXT for more details. Coordinate System : The cartographic coordinate system used for the CRISM data products conforms to the IAU planetocentric system with East longitudes being positive. The IAU2000 reference system for Mars cartographic coordinates and rotational elements was used for computing latitude and longitude coordinates. Media/Format : The CRISM archive will be made available online via Web and FTP servers. This will be the primary means of distribution. Therefore the archive will be organized as a set of virtual volumes, with each data set stored online as a single volume. As new data products are released they will be added to the volume's data directory, and the volume's index table will be updated accordingly. The size of the volume will not be limited by the capacity of the physical media on which it is stored; hence the term virtual volume. When it is necessary to transfer all or part of a data set to other media such as DVD for distribution or for offline storage, the virtual volume's contents will be written to the other media according to PDS policy, possibly dividing the contents among several physical volumes.
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| DATA_SET_RELEASE_DATE |
2010-12-01T00:00:00.000Z
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| START_TIME |
1965-01-01T12:00:00.000Z
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| STOP_TIME |
N/A (ongoing)
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| MISSION_NAME |
MARS RECONNAISSANCE ORBITER
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| MISSION_START_DATE |
2005-08-12T12:00:00.000Z
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| MISSION_STOP_DATE |
N/A (ongoing)
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| TARGET_NAME |
MARS
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| TARGET_TYPE |
PLANET
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| INSTRUMENT_HOST_ID |
MRO
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| INSTRUMENT_NAME |
COMPACT RECONNAISSANCE IMAGING SPECTROMETER FOR MARS
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| INSTRUMENT_ID |
CRISM
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| INSTRUMENT_TYPE |
IMAGING SPECTROMETER
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| NODE_NAME |
Geosciences
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| ARCHIVE_STATUS |
IN QUEUE
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| CONFIDENCE_LEVEL_NOTE |
Confidence Level Overview : The major sources of uncertainty in LDRs arise from uncertainties in instrument pointing knowledge, and from coverage of the MOLA data set. The formal pointing uncertainty for the CRISM gimbal plane is 1 mrad each in the spacecraft yaw(z), roll(x), or pitch/gimbal(y) axes. The formal uncertainty in reconstructed spacecraft attitude is similar. Uncertainty in CRISM's gimbal attitude is negligible, about 0.006 mrad. The formal error in projection onto a surface location depends on the angle of the gimbal and typically is of order several hundreds of meters. Experience during operations suggests that the actual errors are smaller than expected formal errors, so that typical error in surface location is about 200 meters. Latitude and longitude are described by the intersection of CRISM field of view with the MOLA shape model. Given the uncertainties in location of a point on the surface, expected uncertainty near the equator is of the order of 0.005 degrees. Uncertainties in incidence, emission, and phase angles relative to the areoid are similar. Errors in incidence and emission angle relative to the MOLA shape model are dominated by the lower sampling density of the shape model. MOLA points are typically a few hundred meters apart. This compares to CRISM's sampling scale of 15 to 200 meters per spatial pixel, depending on instrument configuration. In areas of smooth topography the errors are small, but in areas with topography that is rough at scales less than a few hundred meters, uncertainty is several degrees. The same uncertainties apply to slope magnitude. LDR Versions : Changes in the processing of LDRs are denoted by incrementing the software version. There is no difference between versions 0 and 1. Known Issue with LDR Accuracy : None. Review : This archival data set will be examined by a peer review panel prior to its acceptance by the Planetary Data System (PDS). The peer review will be conducted in accordance with PDS procedures. Data Coverage and Quality : For each observation, every EDR is compared against frame-by-frame predictions of commanded instrument state. The results of the comparison are written as a data validation report that accompanies the EDRs for that observation. In the case of a hardware or configuration discrepancy (shutter position, lamp status or level, pixel binning, frame rate, channel selection, power status of detectors), processing of the image data to RDR level does not occur in order to avoid introducing invalid results, and LDRs are not created. Also, missing frames or portions of frames are replaced with a value of 65535 (this cannot be a valid data value). That portion of the EDR is not further processed, and it also is propagated to a value of 65535 in all layers of the LDR. Only a subset of instrument configurations represent 'scene' data, as indicated by the keyword MRO:ACTIVITY_ID. Only scene data aimed at Mars' limb have corresponding LDRs. Limitations : None.
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| CITATION_DESCRIPTION |
Murchie, S., Mars Reconnaissance Orbiter Compact Reconnaissance Imaging Spectrometer for Mars Limb Data Record, MRO-M-CRISM-6-LDR-V1.0, NASA Planetary Data System, 2010.
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| ABSTRACT_TEXT |
This dataset is intended to include information on observation conditions of IR and VNIR data cubes from the CRISM instrument on MRO, where the data cubes are pointed at the planet limb. For surface-pointed data cubes, Derived data records are the functional counterpart. The information in LDRs is mapped to the sensor space of non-map-projected data, EDRs and TRDRs.
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| PRODUCER_FULL_NAME |
SCOTT MURCHIE
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| SEARCH/ACCESS DATA |
Geosciences Web Services
Mars Orbital Data Explorer
MRO CRISM LDR FTP Resource
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