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over an area of interest.  EDC has substantial holdings of Landsat data 
from much of the world. As more stations come into operation, however, 
many of the newer images are available only from the local ground 
station operator. With the cooperation of the international ground 
station operators, EDC is compiling a computerized data base of all 
Landsat acquisitions. Descriptors in the data base identify scene 
center point location, cloud cover and quality codes, a scene identi- 
fication number, and the source from which reproductions can be 
acquired. The data base will be supplied to all participating ground 
stations in machine-readable form for their potential use in servicing 
inquiries. 
At EDC we will use this data base to create a series of catalog listings 
for world-wide acquisitions. Called a microCATALOG, the listings are 
available on microfiche in a format that is easily organized into a 
quick reference system. 
All Landsat acquisitions are referenced to a network of "nominal scene" 
centers around which the image center points are clustered. Each 
nominal scene center is assigned to a path, denoting the 251 repetitive 
ground tracks traversed by the satellite. Within the path, the 
sequential scenes are assigned a row number. Thus path 211, row 26 
denotes a nominal scene center nearest Freiburg with geographic 
coordinates of 48°41'N and 7°18'E. By reference to available maps of 
scene centers, a user can easily identify his area of interest in terms 
of path and row intersections. 
The individual microCATALOG fiche are dedicated to a single path, with 
the path number shown in eye-readable header. Within the fiche, sixty 
lists are arranged sequentially by row number. Within each path-row 
intersection listing, the image acquisitions are shown sequentially by 
date. Because of the limit of sixty listings per fiche, it has been 
necessary to arbitrarily divide the paths into three zones - north, 
south, and polar. The north and south zones overlap, so that all 
countries are wholly included within the north or the south zone fiche. 
Our current plans are to update the fiche four times per year for the 
international listings, and monthly for those of North America. They 
are available for purchase at nominal cost, on a one-time order or 
subscription basis. A one-time listing for Western Europe is $12 and 
$35 for the quarterly update subscription. Each updated issue wholly 
replaces the previous issue of microCATALOGS until the limit of listing 
space has been reached.  MicroCATALOG listings of worldwide acquisitions 
held at EDC are currently available. As the international ground stations 
contribute their listings they will be included in future issues of the 
microCATALOG. 
In the immediate future we will be issuing microIMAGE fiche in the same 
format for all images acquired by the U.S. The microimages, of band 5 
data, will enable users to verify cloud location prior to purchase of 
other Data Center products.