PDS_VERSION_ID                   = PDS3
RECORD_TYPE                      = STREAM
OBJECT                           = TEXT
  PUBLICATION_DATE               = 2007-08-15
  NOTE                           = "Description of the GEOMETRY 
    data for the MRO CRISM PDS Archive."
END_OBJECT                       = TEXT
END

                GEOMETRY Data for MRO/CRISM PDS Archive

All geometry data for MRO/CRISM are archived in a separate volume
produced by the Navigation and Ancillary Information Facility (NAIF) at
the Jet Propulsion Laboratory (JPL).   This dataset can be located using
the dataset identifier, which is "MRO-M-SPICE-6-V1.0".  At present, the
data is available through NAIF's online archive at the following URL:

ftp://naif.jpl.nasa.gov/pub/naif/pds/data/mro-m-spice-6-v1.0/mrosp_1000

The following information is taken from the CRISM Archive Volume
Software Interface Specification and the MRO Frames kernel.  It
describes the spice kernels needed for CRISM Pointing calculations.

------------------------------------------------

Geometry Directory Contents  

The Geometry Directory contains a single file, GEOMINFO.TXT, which
directs the reader to the various SPICE kernels that contain the data
necessary to interpret observation geometry.  Four types of SPICE
kernels are needed to calculate CRISM's pointing: 


1) Frames kernel (FK). This file defines the relationships of the of
CRISM's field of view to the spacecraft, with the gimbal at "nadir".
These transformations in frames of reference include: 

 - gimbal base (MRO_CRISM_BASE) -> spacecraft (MRO_SPACECRAFT) 
 - optical axis at gimbal "nadir" (MRO_CRISM_OSU) ->
                                        gimbal base (MRO_CRISM_BASE)  
 - The gimbal C kernel defines the relationship of optic axis at a
   gimbal position to the gimbal nadir 
 - IR zero position for IK (MRO_CRISM_IR) -> optical axis
   (MRO_CRISM_OSU); nominal there two are coaligned and offsets of the
   IR FOV from the optical axis are entirely accounted for in the IK  
 - VNIR zero position for IK (MRO_CRISM_VNIR) -> optical axis
   (MRO_CRISM_OSU); nominal there two are coaligned and offsets of the
   VNIR FOV from the optical axis are entirely accounted for in the IK
   Graphically, this is: 

             MRO_SPACECRAFT 
                  | 
                  | <--- fixed
                  | 
             MRO_CRISM_BASE 
                  | 
                  |<--- gimbal ck 
                  | 
               MRO_CRISM_ART
                    |  
                    |<--- fixed  
                    |  
               MRO_CRISM_VNIR 
                    |
                    | <--- fixed
                    |
               MRO_CRISM_IR 

  The CRISM frames kernel is delivered to NAIF and is incorporated into
  the MRO frames kernel. 

2) Instrument kernel (IK). This file describes the relationship of
position of each detector element (at a row or wavelength and spatial or
column position) to a zero position within the field of view. Nominally,
that is in the VNIR row closest to 610 nm or the IR row closest to 2300
nm, at the column position closest to the optical axis. Due to keystone
distortion, there is a different relationship for every row number of
either detector.  The CRISM instrument kernel is delivered to NAIF. 

3) Gimbal C kernel. This file gives a time history of the angle of the
gimbal within the gimbal plane, relative to its defined nadir. It is
constructed from gimbal attitude measurements in image headers, i.e.,
from the TAB file part of an EDR. One file covers a 1 operational day
time span of CRISM data.  CRISM gimbal C kernels are delivered to NAIF who
will merge them into longer time spans. 

4) Metakernel. This file gives, for any time span covered by a gimbal
C-kernel, the MRO and CRISM SPICE kernels used to create DDRs for
observations occurring during that time period. Note that kernels are
loaded in the order listed., so the highest priority kernel is listed
last.  The kernels listed in the CRISM metakernels are recorded in the
SOURCE_PRODUCT_ID label keyword of resulting products delivered to the
PDS Geoscience Node. 

The file naming convention CRISM-generated SPICE kernels is as follows. 
   MRO_CRISM_(KernelType)_(YYYY_DOY)_(Filetype)_(version).(Ext) 
 where: 
    Kernel Type =  

  FK (frames kernel) 
  IK (instrument kernel) 
  CK (gimbal C-kernel) 
  MK (metakernel) 

  YYYY_DOY is the year and day of year of the start of a 2-week period
  covered in a single gimbal C kernel or metakernel; or else these
  fields are filled with zeroes.

  filetype =  
    P for predicted 
    R for reconstructed 
    N for not applicable 
  version  = 0, 1,...,9, a, ..., z 
  Ext  =  
    TI (text-format, instrument kernel) 
    TF (text-format, frames kernel) 
    BC (binary-format, gimbal C kernel) 
    TM (text-format, metakernel)