File Name Convention
--------------------
This NOAA/NESDIS albedo data set is made up of three sets of data 
files on three common Earth grids with spatial resolutions of 1 degree, 0.5 
degree, and 0.25 degree in both latitude and longitude:
 
1) monthly albedo files (ASCII format map files). 

2) "difference" table files (with an extension of ".dif") that hold all the
   points from each albedo map that did not match the ISLSCP II land/water mask,
   and were either removed or added through interpolation (one for each albedo
   map).

3) a "change map" showing those points that were different from the ISLSCP II
   land/water mask and were thus removed or added (ASCII map file). 

The three sets of files are named using the following naming convention:

1) noaa_albedo_5year_XX_mZZ.asc: 12 Gridded monthly albedo map files, where XX
   can be either "1d", "hd", or "qd" for spatial resolutions of 1 degree, 1/2 
   degree, or 1/4 degree, respectively, in both latitude and longitude. ZZ is the
   month from 01 to 12. Note that this albedo data set represents the monthly
   average using data from a five-year period from April 1985-December 1987 and
   January 1989-March 1991.

2) noaa_albedo_5year_XX_mZZ.dif: 12 ASCII tables of "differences", or points in
   the original file that did not match the ISLSCP II Land/water mask, and were 
   removed from or added to the ASCII map files.

3) noaa_albedo_5year_XX_chngmp.asc: Gridded ASCII map showing the differences 
   between the ISLSCP II land/water mask and the original data set: All points
   with negative values ("-1") are those where the ISLSCP II mask showed water but 
   where the original data set showed land. All points with a value of zero are 
   those points where the two land/water masks agreed and all points with 
   positive values were land points with no data over land in the original data
   set which were filled in from interpolation. There is one file per spatial
   resolution.


ASCII File Format
------------------
All of the files in the ISLSCP Initiative II data collection are in the standard 
ARCGIS ASCII GRID, or text format. The file format consists of numerical fields 
of varying length, which are delimited by a single space and arranged in columns 
and rows. 
The files at different spatial resolutions each contain the following numbers of 
column and rows:
     One degree: 360 columns by 180 rows 
     1/2 degree: 720 columns by 360 rows 
     1/4 degree: 1440 columns by 720 rows 

All values are written as floating point values, expressed as a percent albedo, 
and the 'change maps' are given as integer values ranging from -1 to 5. Missing 
values over water are assigned the value of -99. Missing values over land (such 
as Greenland and Antarctica) are assigned the value of -88.

The ASCII map files (with the extension of ".asc") have all had the ISLSCP II 
land/water mask applied to them. All points removed from the original files 
are stored in "differences" files (with the extension ".dif"). These ASCII 
files contain the Latitude and Longitude location of each removed point (center
of the pixel in decimal degrees), and the data value at that point. At the 
bottom of these files are also a list of all points added to the file through 
interpolation, where the land/water mask indicated land but there was no data in 
the original file. There is also a column called "Interpolation_Level" that 
contains the number of times the interpolation routine was run to get a value 
for that point (see full documentation). The higher the number, the less 
reliable the value is. There is one ".dif" file for each ASCII map file.

The "change map" files show the results of applying the land/water mask, as
a viewable ASCII map: all points added (positive number, containing the 
"Interpolation_Level"), all points unchanged ("0"), and all points removed 
("-1"). There is one file per spatial resolution

The files are gridded to a common equal-angle lat/long grid with a spatial 
resolution of 1 degree lat/long, where the coordinates of the upper left corner 
of the files are located at 180 degrees W, 90 degrees N and the lower right corner
coordinates are located at 180 degrees E, 90 degrees S. Data in the files are
ordered from North to South and from West to East beginning at 180 degrees West
and 90 degrees North.