PDS_VERSION_ID                = PDS3
RECORD_TYPE                   = STREAM
OBJECT                        = TEXT
  PUBLICATION_DATE            = 2000-07-26
  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 two resolutions, one-quarter degree of
latitude and longitude and one-eighth degree. The data are in image
format, whereas in version 1 they were ASCII tables.  The images have
16-bit signed integer pixels, and are described by accompanying detached
PDS labels. At each resolution, four images are present: areoid radius,
mean planetary radius, median topography, and counts (number of
observations at each point).  File names are in the format IEGrrr[r]t.IMG,
where rrrr represents the grid resolution (0125 for one-eighth degree,
025 for one-quarter degree) and t is the image type: A (areoid), R
(radius), T (topography), or C (counts).  The images 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.