auspices of the NASA EOS Program in cooperation 
with the USGS, NOAA, the European Space Agency, 
and a worldwide network of AVHRR ground reception 
and data processing facilities. The primary objective 
of the project is to obtain complete 1-year coverage 
of all the land surfaces of the globe with 1-km 
AVHRR sensor data serving as a precursor data set 
for EOS investigators involved in the development of 
scientific algorithms and models. 
One of the products being derived from the Global 
Land 1-km AVHRR Data Set is a 10-day global 
vegetation index composite that will allow scientists to 
experiment with vegetation index information on a 
global scale at the 1-km resolution. At full resolution, 
a single 10-day composite product represents 10 GB 
of data. The media being used to distribute these 
composites are 8-mm high-density cassette tapes. This 
medium was chosen because it required the fewest 
tapes and the least amount of operator involvement 
(see table 1). The time estimates provided in table 1 
include computer write time only and do not include 
time for operator tasks such as tape mounting and 
dismounting and tape labeling. Therefore, even though 
the wall-clock time required to write a 10-GB composite 
to 8-mm high-density cassettes was 3 hours more than 
the time required to write the same composite to write- 
once compact disk (CD), it would be significantly more 
expensive operationally to handle and disseminate the 
15 CD's. Also, it was felt that the users would prefer 
having a significantly smaller number of media. 
Network delivery of a complete 10-GB composite is not 
a practical alternative. For example, assuming that a 
remote user has a moderately robust connection to the 
Internet (25-50 kilobytes per second), it is estimated 
that it could take from 2.3 to 4.6 days to transfer a full 
10-GB composite. This scenario further assumes that 
the computer systems and network connections at both 
ends remain up throughout the period and that sufficient 
disk storage capacity is available to hold the data 
without operator intervention. 
Assuming that most users would seldom require 
complete 10-day composites but would be interested in 
smaller geographic regions from one or more 10-day 
composites, the Center is exploring the use of data 
subsetting and compression techniques to provide a 
more effective network data delivery alternative. The 
Center is developing a capability for users to select, for 
network transfer, a geographic subset of a 10-day 
composite at a resolution of from 1-16 km. The 
selection would be done through a graphical user 
interface accessed by means of the EOS Data and 
Information System's interactive data query and order 
system, the Information Management System. A 
prototype of this capability should be available for 
demonstration and science-user feedback in July 1994, 
with a fully operational capability planned for October 
1994. 
7. SUMMARY 
The EROS Data Center holds the world's largest 
collection of satellite- and aircraft-acquired images of 
the Earth's land surface, including more than 3 million 
Table 1: Media options for 10-GB composite product. 
  
  
Media Type Capacity | Number . Write - 
Time 
6250 bpi 9-track .16 GB 63 16 hrs. 
3480 cassette .30 GB 34 9 hrs. 
CD Write Once (6x) .68 GB 15 3 hrs. 
4mm cassette 2.0 GB 5 15 hrs. 
8mm cassette (low) 2.3 GB 5 15 hrs. 
8mm cassette (high) 5.0 GB 2 6 hrs. 
  
satellite images and more than 7 million aerial 
photographs. In its role as the National Satellite Land 
Remote Sensing Data Archive, the Center is exploiting 
new technologies to ensure the long-term availability of 
these data. The Center is converting its Landsat MSS 
and TM satellite data from high-density instrumentation 
tapes to DCRSI cassette tapes. In conjunction with the 
media conversion effort, the Center has successfully 
recovered more than 15,000 Landsat scenes from 
nearly 700 archive tapes affected by hydrolysis. This 
recovery was accomplished by applying low levels of 
heat to the tapes to effect a temporary reversal of the 
hydrolysis. 
The Center is also investigating and implementing new 
techniques to improve the quality and accessibility of 
products and services. For example, the Landsat 
media conversion effort is providing the opportunity to 
assess the overall quality of the Landsat archive data 
and metadata and to collect digital browse images for 
user viewing through state-of-the-art information 
systems, such as GLIS. 
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. As 
part of these activities, the Center is exploring the use 
of data subsetting and compression techniques to 
provide an effective network data delivery capability for 
the 10-day global vegetation index composite products. 
SELECTED REFERENCES 
Cuddihy, E.F., 1980. The Aging of Magnetic 
Recording Tape. IEEE Transactions on Magnetics. 
Volume 16, Number 4, July 1980, p. 558. 
Cuddihy, E.F., 1976. Hygroscopic Properties of 
Magnetic Recording Tape. IEEE Transactions on 
Magnetics. Volume 12, Number 2, March 1976, p. 
126-135. 
DeLancie, P., 1990. Sticky Shed Syndrome: Tips On 
Saving Your Damaged Master Tapes. In: Mix 
Magazine, May 1990, p. 148-152. 
Holm, T.M., W.C. Draeger, R.R. Risty, 1993. 
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