These biweekly Gallo experimental GVIs were computed as described in the
printed documentation from operational NOAA weekly GVIs available from
the Satellite Data Services Division (address in the main README file in 
the root directory of this CD-ROM, reprinted in the hardcopy documentation),
using prelaunch calibration data available from the same source.  

These are the original data computed by Kevin Gallo, NOAA/NESDIS Office of 
Research and Applications, at the EROS Data Center in South Dakota.  They 
are provided as an archive of Gallo's results, and as a source of additional
compilations (such as monthly or seasonal averages) by the user.

These data have not been checked for quality.  The accompanying monthly 
values in latitude-longitude projection were found to be misregistered.  
This suggests caution if you want to use these biweekly data with other
data in a Mercator projection.

Note that the data for 1985 on the original CD-ROMs were incorrect.  The
correct data for 1985 are provided here.

This collection of data is sorted into four subdirectories:

The ADOC subdirectory contains IDRISI 3.X .doc files derived directly from the 
data, using the IDRISI function DOCUMENT.  These data have been placed adja-
cent to the file allocation table, to optimize the use of the IDRISI function 
LIST, which accesses both the file allocation table and the .doc files.  

The BDOC subdirectory contains IDRISI 3.X .doc files containing identical ma-
xima and minima.  This version of the .doc files will ensure consistent color 
representations when using the IDRISI function COLOR A (which autoscales the 
8-bit values to fit the 16-color VGA display).

There is no CDOC subdirectory for this version of the data.  As of this 
writing, IDRISI 4.0 does not handle the Mercator projection.  You should 
use your choice of ADOC or BDOC when running IDRISI 4.

The CELL subdirectory contains simple 8-bit raster grids.  These data are 
identical to GRASS CELL files, to IDRISI 8-bit image files, and are a de-facto 
standard for raster data interchange.  Such data have been proven to be rela-
tively simple to import into many spatial analysis (image analysis and geo-
graphic information) systems.  PLEASE REMEMBER THAT THESE DATA ARE NOT
DIRECTLY COMPATIBLE WITH THE GLOBAL CHANGE DATA BASE.  THEY HAVE NOT
RECEIVED THE GCDB'S QUALITY CONTROL OR PEER REVIEW.  THEY ARE NOT IN
A COMPATIBLE SCALE OR PROJECTION.  The data are probably internally 
consistent, so files within this compilation can probably be intercompared,
in the context that one should work while working with GVIs.  They should
be considered experimental.

The CELLHD subdirectory contains GRASS 3.X (compatible with GRASS 4.X) cell 
header files.  Depending on how you organize your global latitude-longitude 
data you may want to change the "north:" "south:" "east:" "west:" "n-s resol:" 
and/or "e-w resol:" entries, particularly if you want to register these to
other data in a Mercator projection.  Note that the CELLHD entries are of 
the format FILENAME.IMG.  The .IMG extension is required for compatibility 
with the naming of the CELL files, which is a compromise allowing operation 
of this CD-ROM in both GRASS and IDRISI.  As the Mercator projection is not
supported in GRASS, there are no optimized GRASS4 CELLHD files for the
biweekly data (unlike the monthly data).

=============================

To use these data in GRASS, you have the minimal CELL and CELLHD directories.
Remember that the naming convention for GRASS is FILENAME.IMG.  You will
probably want to copy data that you want to use often to your hard disk,
and to run the GRASS support program (support in GRASS3.X, r.support in
GRASS 4.X) to add appropriate color tables, build histograms and legends, 
and add documentation to the file(s).

You may want to link the CELL and CELLHD subdirectories in this CD-ROM to
those in a global data base on your hard disk.  The files created by
support (or r.support) would then be written to appropriate subdirectories
on your hard disk.

==============================

To use these data in IDRISI, use the DOS APPEND command as follows:

APPEND /E
APPEND DRIVE:\2BIWEEK\CELL; DRIVE:\2BIWEEK\ADOC       or

APPEND /E
APPEND DRIVE:\2BIWEEK\CELL; DRIVE:\2BIWEEK\BDOC

If you want to use standardized colors when autoscaling (COLOR A), use the
second line.  If you want to do computations using the actual value ranges
of each GVI file, use the top line.  Notice that the only difference between
these two commands is in the last "word" which is ADOC or BDOC, depending
on which .doc files you want to use with the .img files in the CELL 
subdirectory.

===============================

Both of these procedures may appear slightly different from the way you
may use GRASS or IDRISI.  But they allow the same CD-ROM to be used as
a (albeit slow) form of mass storage for both of these widely available 
analysis systems, both designed for global environmental analysis.

=================================