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CDDIS Bulletin - February 1991
Volume 6 No. 3
In this issue:
On the cover: Global VLBI Site Locations
The first European Remote Sensing Satellite (ERS-1), scheduled
for launch in April-May 1991, will utilize advanced microwave techniques
to measure various ocean parameters such as sea state, sea surface
winds, ocean circulation, and sea/ice levels as well as all-weather
imaging of the ocean, ice, and land surfaces. The ERS-1 spacecraft
is equipped with laser retro-reflectors and will be tracked by laser
ranging systems. The Crustal Dynamics satellite laser ranging (CDSLR)
stations will be joining the SLR stations located worldwide in support
of the ERS-1 satellite by providing tracking on a daily basis. The
CDDIS has been tasked to support the ERS-1 project by providing a
repository for both quick-look and full-rate SLR data for analysis
by the ERS-1 POD (precision orbit determination) team located at
the German Processing and Analysis Facility (D-PAF) located in Oberpfaffenhofen
in Germany.
Quick-Look Data. Figure 1 illustrates the flow of
ERS-1 quick-look data from the SLR station to D-PAF. All CDSLR stations
will transmit their quick-look data to Bendix CDSLR headquarters
located in Greenbelt, MD; foreign sites, however, will send their
data directly to D-PAF. Bendix will deposit the CDSLR quick-look
data into the CDDIS on a daily basis (Monday thru Friday). D-PAF
can then access CDDIS via electronic networks to retrieve these data
sets and in turn, deposit data from foreign sites. By utilizing this
procedure, D-PAF will typically receive quick-look data from the
global set of stations within a maximum of three days after the observation
day. All ERS-1 quick-look data for a period of several weeks will
be archived on-line on the CDDIS MicroVAX. CDDIS staff will summarize
each data file transferred on a daily basis. These summaries will
be loaded into the CDDIS data base for generation of weekly and monthly
tracking status reports. Full-Rate Data. The CDDIS will
also archive the global ERS-1 full-rate data set. The flow of full-rate
data to the CDDIS is illustrated in Figure 2. Merging of the CDSLR
and foreign data sets will not be performed. These data will be available
to interested parties on a per request basis. The ERS-1 data will
be available in the MERIT II format.
The CDSLR network and the CDDIS will also support the future TOPEX/POSEIDON
mission and its POD analysis in a similar fashion to ERS-1.
The CDDIS GPS data archive now contains the GORF, Greenbelt, MD,
Hat Creek, CA, and Quincy, CA footprint data sets. A local survey
at the Hat Creek site using GPS was also performed. The data are
available in raw, binary (Trimble receiver) and RINEX formats. Details
on the current CDDIS archive of CDP-sponsored footprints are given
in the table below.
Table. Footprint Data in CDDIS
Start End No. of No. of
Footprint Site Date Day Date Day Monuments Sessions
Fort Davis, TX 07-Jun-90 157 20-Jun-90 157 8 56
GORF, Greenbelt, MD 03-Oct-90 276 19-Oct-90 292 5 46
Quincy, CA 03-Nov-90 307 08-Nov-90 312 4 24
Hat Creek, CA 12-Nov-90 316 21-Nov-90 325 8 40
Brian Lev, Jerome Bennett (NASA/GSFC Code 930.4)
Effective December 1, NASA has made major changes in how it manages its computer
networks. The individual entities known as "SPAN" (the Space Physics Analysis
Network) and "NSN" (the NASA Science Network) no longer officially exist; instead,
the two networks have been merged into the common NASA Science Internet (NSI),
which utilizes both the DECnet and TCP/IP protocols. Under the new arrangement,
the Ames Research Center is responsible for NSI management and operations,
and the Goddard Space Flight Center is responsible for NSI user support.
As a result of these changes, Goddard's Advanced Data Flow Technology Office
(ADFTO, Code 930.4) will be providing direct support for all NSI users. Under
the aegis of the ADFTO, NSI users will be offered a full range of support services
that will be expanded over the next several months. Beginning with a help desk
(available via electronic mail and telephone), plans include a toll-free telephone
number, dedicated FAX machine, and a variety of automated servers.
Anyone interested in more information on the changes in NASA networking management
or on the NASA Science Internet should contact the new NSINIC (NSI Network
Information Center) by calling either (301) 286-7251 or (301) 286-9514 (FTS
888-7251 or 888-9514), or by sending electronic mail to DFTNIC::DFTNIC (NSI-DECnet)
or dftnic@dftnic.gsfc.nasa.gov (NSI-TCP/IP).
This section is designed to give brief notices of special events, new data
sets, or problems encountered in recent months.
The CDDIS has recently received the USNO's NAVNET data bases from September
1988 through June 1990. These data sets are in VLBI data base handler (DBH)
format but can be converted to NGS card-image format upon request. Users interested
in receiving copies of any of these data sets should contact the CDDIS staff.
At a recent CSTG SLR meeting held at GSFC on October 23, 1990, the group
recommended that future SLR data releases contain operational and engineering
data in a single merged data set. Prior to this decision, engineering data
was released to the CDDIS on a monthly basis on a separate release tape. In
the merged form, data classified as engineering can be identified by a release
flag set to Z; operational data has a release flag of A, B, C, etc. When/if
engineering data is considered operational, the release flag will be updated
from Z to the current value for the release flag (e.g., B, C, etc.). This policy
will become effective with all CDDIS releases after February 1, 1991.
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