 
 
MRO CRISM Gimbal Orientation CK File for Primary Science phase, 2007-03
===========================================================================
 
     Created on Fri Jun 1 14:19:23 PDT 2007.
 
 
Orientation Data in the File
--------------------------------------------------------
 
     This file contains actual orientation for the Mars Reconnaissance
     Orbiter (MRO) Compact Reconnaissance Imaging Spectrometer for Mars
     (CRISM) instrument. It provides the orientation and angular rate
     of the 'MRO_CRISM_ART' frame (frame ID -74012) with respect to the
     'MRO_CRISM_BASE' frame (frame ID -74011).
 
 
Status
--------------------------------------------------------
 
     This file was created by NAIF by merging daily CRISM CK files
     generated by the CRISM Team. This file is intended for archiving
     with the Planetary Data System (PDS).
 
 
Pedigree
--------------------------------------------------------
 
     The original daily CK files used to create this file were made
     during operations by the CRISM Team. These files contained the
     orientation of the gimbal frame computed using the gimbal angles
     from the instrument's housekeeping telemetry included in the CRISM
     EDR files. At the time of archive preparation the CRISM team
     provided CRISM CK daily files to NAIF. These files were merged
     together using DAFCAT and augmented with these comments (see
     Appendix 1 for the complete list of original daily files used to
     make this file).
 
     To make the daily CKs, the crism_ck program (version 1.2, linked
     against version N0061 of the SPICE toolkit) was run on a complete
     set of EDRs for a given day to collect the gimbal angle, scan
     start time, and scan rate information from these EDRs, compute
     gimbal frame orientation quaternions corresponding to the angles,
     compute associated times and store these time tagged quaternions
     in a single Type 3 segment in the output CK file for that day.
 
     A CK interpolation interval was created to match the time period
     covered by data stored in a single CRISM EDR. For neighboring EDRs
     that overlapped, distinct interpolation intervals were merged to
     create a single interval and stored in the CK. When data was
     collected by both detectors simultaneously, gimbal encoder
     positions from both EDRs were interleaved within this merged
     interpolation interval. In this situation, the CK contained
     a triplet of pairs of points, yielding 6 quaternion entries for 2
     simultaneously acquired frames, one for VNIR and one for IR.
 
     For each frame from the source EDR files three gimbal positions
     associated with three time tags were included into the CK:
 
                       SCANSTR       SCANMID       SCANEND
          -------/~ ~/----|-------------|-------------|------/~ ~/---
                          |             |             |
                          |- 1/2 * GAP -|             |
                          |                           |
                          |----- 1 / FRAME_RATE ------|
 
     where:
 
          SCANSTR,    are the start, middle, and end times of the CRISM
          SCANMID,    frame for which gimbal attitude is to be placed in
          SCANEND     the CK. The scan start time is computed from
                      EXPOSURE_SCLK_S and EXPOSURE_SCLK_SS (secondary
                      time). The other scan times are derived from
                      SCANSTR as follows:
 
                         SCANMID_time = SCANSTR_time + 0.5/FRAME_RATE
                         SCANEND_time = SCANSTR_time + 1.0/FRAME_RATE
 
          FRAME_RATE  is 1.0, 3.75, 5.0, 15.0, or 30.0. The RATE from
                      CRISM EDR determines which FRAME_RATE to use. The
                      time between SCANSTR time and SCANEND time is
                      1/FRAME_RATE, in seconds.
 
     The angles associated with the SCAN time were computed from
     SCAN_MOTOR_ENCPOS1, SCAN_MOTOR_ENCPOS2, and SCAN_MOTOR_ENCPOS3 of
     CRISM EDR. The gimbal angles were derived from following formula:
 
          ANGLE = - PI / (2^21) * SCAN_MOTOR_ENCPOS
 
     where -PI/(2^21) is the conversion from encoder counts to radians.
 
     For low frame rates ( 1.0 Hz, 3.75 Hz and 5.0 Hz ), all three
     gimbal attitude samples mentioned above (start, middle, end) were
     stored along with their associated times, as described above.
 
     For higher frame rates ( 15.0 and 30.0 Hz), a lossless compression
     scheme was utilized. Operationally, the gimbal was intended to be
     at a fixed gimbal position while data was collected at these
     higher frame rates. As a result, all gimbal attitude positions
     should have had the same value. In practice, there was a small
     amount of acceptable jitter or noise associated with these gimbal
     encoder position values. For the period of time where data was
     collected at higher frame rates, an average value was computed
     from these gimbal encoder position samples. This period of time
     was then represented as a single interval in the CK where both
     the start and end times of the interval has a constant gimbal
     angle equal to this average value.
 
     The quaternion was computed by the angular rotation around the
     Z-axis:
 
          QUAT = [ cos(ANGLE / 2), 0, 0, - sin(ANGLE / 2) ].
 
     The orientation data was augmented with angular rates computed by
     numeric differentiation to allow for usage of the high level SPICE
     APIs that deal with states and states transformations.
 
 
Approximate Time Coverage
--------------------------------------------------------
 
     This file covers the following interval of the Primary Science phase
     of the mission:
 
          Coverage Begin UTC       Coverage End UTC
          ------------------------ ------------------------
          2007-MAR-01 00:00:10.617 2007-MAR-31 23:54:32.833
 
     It is important to note the CRISM gimbal attitude C-kernels are
     inherently full of gaps. Essentially there exists a single
     interpolation interval for data covered by a single CRISM EDR or
     collection of time-overlapping CRISM EDRs.
 
     To determine the specific time coverage of this file, use the NAIF
     tool CKBRIEF as follows:
 
          % ckbrief -dump -utc SCLK_FILENAME LSK_FILENAME CK_FILENAME
 
     This will produce a table of interpolation intervals supplied by
     the file. There should nominally be a 1:1 mapping between
     intervals and CRISM EDRs or sets of overlapping EDRs.
 
     The SCLK file provided on the line above is used as an example. Be
     sure to use the latest SCLK kernel available to perform any
     operations using CKBRIEF.
 
 
Usage Note
--------------------------------------------------------
 
     To make use of this file in a typical SPICE based application, you
     must supply a leapseconds kernel, a MRO spacecraft clock kernel,
     and the MRO frame kernel. These files provide the supporting
     ancillary data to properly query this C-kernel for attitude
     content.
 
 
Contacts
--------------------------------------------------------
 
     If you have any question regarding this data, contact:
 
          Scott Murchie and the CRISM Operations Team
          The Johns Hopkins University Applied Physics Laboratory
          +1 (240)228-6235
          Scott.Murchie@jhuapl.edu
 
     or NAIF:
 
          Boris V. Semenov
          (818)-354-8136
          boris.semenov@jpl.nasa.gov
 
 
Appendix 1: List of the original CK files
--------------------------------------------------------
 
spck_2007_060_r_1.bc
spck_2007_061_r_1.bc
spck_2007_062_r_1.bc
spck_2007_063_r_1.bc
spck_2007_064_r_1.bc
spck_2007_065_r_1.bc
spck_2007_066_r_1.bc
spck_2007_067_r_1.bc
spck_2007_068_r_1.bc
spck_2007_069_r_1.bc
spck_2007_070_r_1.bc
spck_2007_071_r_1.bc
spck_2007_072_r_1.bc
spck_2007_081_r_1.bc
spck_2007_082_r_1.bc
spck_2007_083_r_1.bc
spck_2007_084_r_1.bc
spck_2007_085_r_1.bc
spck_2007_086_r_1.bc
spck_2007_087_r_1.bc
spck_2007_088_r_1.bc
spck_2007_089_r_1.bc
spck_2007_090_r_1.bc
 
 
