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.
Availability of Earth Observations Data From The
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