PDS_VERSION_ID                = PDS3
RECORD_TYPE                   = STREAM
OBJECT                        = TEXT
  PUBLICATION_DATE            = 2001-04-10
  NOTE                        = "Description of the DATA
     directory contents on MGS MOLA PEDR archive volumes"
END_OBJECT                    = TEXT
END


                   DATA Directory Contents

     The DATA directory contains MOLA PEDR, EGDR, and SHADR data 
products in three subdirectories. 

     The EGDR subdirectory contains version 2 of the MOLA global
topographic gridded data set at a resolution of 1/32 degrees of latitude
and longitude per pixel. The data are in image format, whereas in
version 1 they were ASCII tables.  The image has 16-bit signed integer
pixels, and is described by an accompanying detached PDS label. At the
1/32 degree/pixel resolution, only the topography image is present,
although releases of this data at lower resolutions included additional
images for areoid radius, mean planetary radius, and counts (number of
observations at each point).  Because the image files are so large it
was decided to include only the topography image, as it is the one
likely to be of greatest interest.  The other images are available upon
request from the PDS Geosciences Node.  File names are in the format
IEGrrrrt.IMG, where rrrr represents the grid resolution (0031 for
one-eighth degree) and t is the image type (T for topography).  The
image can be displayed using NASAview image display software, available
from the PDS at no charge. NASAview can be downloaded from the PDS Web
site at http://pds.jpl.nasa.gov/.

     The PEDR subdirectory contains binary data files with attached
PDS labels. The file names have the format APnnnnnv.B, in which
nnnnn is the orbit number and v is a letter representing the product
version. The orbit number is equal to the MGS Project orbit number
plus 10000. (This is done to ensure a unique product ID; MGS orbit
numbers started over at 1 at the beginning of the Mapping Phase, but
MOLA had already acquired data before the Mapping Phase using the
pre-mapping orbit number as part of the product ID.) PEDR data files
acquired during the Mapping Phase are aggregated by day; therefore
one PEDR file contains multiple orbits.

     The SHADR subdirectory contains the MOLA spherical harmonics
topography model. The model is a numerical transform of the MOLA
MOLA 0.5-degree EGDR into spherical harmonics using Simpson's Rule
quadrature. It consists of two ASCII tables, a header table and
a coefficients table, contained in the file GTM070AA.SHA and described
by a detached PDS label in GTM070AA.LBL.