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several times and still achieve successful recovery. 
4. THE GLOBAL LAND INFORMATION SYSTEM 
The Global Land Information System (GLIS) is an online 
data directory, guide, and inventory system developed 
by the USGS to respond to the land data information 
and access needs of the U.S. global change research 
community. GLIS can best be characterized as a 
metadata system containing descriptive information 
about data sets and the associated functions that allow 
scientists to assess the potential utility of data sets, 
determine their availability, and place online requests for 
related data products. 
The data set information in GLIS is maintained in three 
levels of detail -- the directory, guide, and inventory. 
The GLIS directory contains summary descriptions of 
entire data sets. Users can query the directory by using 
any combination of keywords (discipline, location, 
geophysical parameter), acquisition date, data source 
(spacecraft, sensor), geographic coverage, project, and 
investigator. The GLIS guides contain detailed 
descriptions of entire data sets, including such 
information as sensor specifications, extent of coverage, 
processing history, data quality, and product availability. 
The GLIS inventories contain detailed information about 
individual data set entities such as a Landsat scene. 
GLIS contains inventories of U.S. and foreign holdings 
of Landsat MSS and TM data, as well as the Center's 
holdings of National Oceanic and Atmospheric 
Administration (NOAA) Advanced Very High Resolution 
Radiometer (AVHRR) sensor data. GLIS supports 
temporal-, spatial-, and parameter-oriented queries of 
inventories, and the spatial query options include point, 
bounding rectangle, polygon, and geographic name 
searches. 
In addition to providing the text-based directory, guide, 
and inventory query functions, GLIS also offers several 
graphical aids to users. Among these are capabilities 
for map-based geographic query specification and 
coverage plotting, and online digital image browse 
services for selected data sets. The map-based tools 
allow users to specify the area they wish to search by 
interactively "drawing" this rectangular or polygonal area 
on a map, or alternately by requesting to view the 
geographic coverage of their query results. The image 
browse services are primarily intended to allow users to 
visually judge overall image quality, determine the 
extent of cloud cover, and verify geographic coverage. 
GLIS currently contains more than 60,000 AVHRR 
browse images and soon will have the first set of 
Landsat MSS browse images being generated by the 
TMACS systems. These graphical aids are available to 
users through an X-windows-based, 32-bit graphics 
workstation interface called X-GLIS. 
Although GLIS provides information about and access 
to a variety of regional, continental, and global land 
science data sets, these query and selection aids have 
proven particularly useful to those who are interested in 
selecting and ordering data from large satellite data 
inventories. For example, through GLIS a user can 
execute a query of the 600,000-scene Landsat MSS or 
the 60,000-pass AVHRR inventories, see the 
geographic coverage of individual scenes or passes 
plotted on a map, and request to view individual browse 
images for final selection and ordering. 
5. GLIS USER ACCESS AND ASSISTANCE 
Users who want to perform graphic-based queries can 
use an X-terminal or X-terminal emulator package on a 
PC. 
From INTERNET: $TELNET xglis.cr.usgs.gov 
Users who want to perform text-based queries can use 
an alphanumeric terminal or a terminal emulator 
package on a PC. 
From INTERNET: $TELNET glis.cr.usgs.gov 
or STELNET 152.61.192.54 
Direct Dial: Set modem to 8 bits, no parity, 
1 stop bit Dial: (605) 594-6888 
For information concerning system access and how to 
obtain a copy of the graphical interface software, 
contact GLIS User Assistance through one of the 
following: 
Telephone: 1-800-252-GLIS (1-800-252-4547) 
or commercial: (605) 594-6099 
E-mail: GLIS@GLIS.CR.USGS.GOV 
Mail: U.S. Geological Survey 
EROS Data Center 
GLIS User Assistance 
Sioux Falls, SD 57198 USA 
6. SATELLITE DATA DISTRIBUTION 
Despite the dramatic improvements in digital data 
storage and transfer capacities that have been achieved 
over the past 20 years, data volume continues to be 
one of the most challenging aspects of satellite data 
distribution. Many of the same technological advances 
that have enhanced a data provider's ability to deliver 
large digital data products effectively and efficiently 
have also enhanced the producer's ability to generate 
such products. Factors such as greater spatial 
resolution and more spectral channels combined with 
powerful state-of-the-art computer systems and 
expanded communications band-widths, have all 
contributed to the generation of larger and larger 
satellite data sets. 
One example of this challenge now facing the Center 
stems from its participation in NASA's EOS program. In 
preparation for its role as an EOS data archive, 
processing, and distribution facility, the Center is 
participating in early prelaunch activities to enhance the 
availability and utility of existing Earth science data. 
One such activity is the Global Land 1-km AVHRR Data 
Set project. This project is being conducted under the 
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