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CDDIS Bulletin - October 1990
Volume 6 No. 1
In this issue:
On the cover: Alaska 1990 GPS Campaign -- Revised
The CDDIS has recently begun the archive of Global Positioning
System (GPS) data for the Crustal Dynamics Project. This archive
includes several different categories of GPS experiments: local,
intercomparison surveys between existing SLR and VLBI monuments,
regional surveys, and footprint surveys. Local surveys between SLR
and VLBI monuments can be utilized for intercomparison of the analysis
(e.g., site positions and baselines) derived from space geodetic
techniques. A recent GPS experiment was conducted by personnel from
the Onsala Space Observatory in Sweden to tie connecting the VLBI
antenna at La Silla, Chile (operated by Onsala) and the NASA mobile
SLR site at Cerro Tololo, Chile. Three sites were occupied during
this three-day survey: La Silla, Cerro Tololo, and Condoriaco, Chile.
A recent regional survey of Alaska coordinated by NOAA/NGS for
the Alaska Department of Transportation occupied nearly thirty sites
(see cover) throughout Alaska and Canada, including eight mobile
VLBI sites and the fixed VLBI site at Fairbanks. Eight NASA-owned
receivers (four from GSFC and four from JPL) were loaned to this
experiment. The data from this experiment has been transferred electronically
from the Gilmore Creek Geophysical Observatory near Fairbanks to
the CDDIS using NSI. Table 1 lists the sessions observed in this
Alaska campaign and available in the CDDIS.
Starting this summer, the CDP GSFC receivers have been utilized
to support studies in the geophysical integrity of the Project's
SLR and VLBI sites. Small networks of GPS sites have been selected
in an approximate 10-20 km radius around the main observing monuments
at several of key CDP sites. The measurements taken at these "footprint" sites
will allow analysts to estimate the local tectonic stability of the
area they encompass, assuring the integrity of the Project's space
geodetic measurements taken at these critical sites. In addition
to the surrounding footprint sites, measurements are taken at the
reference monuments placed at a distance of 50 to 100 meters to the
main marker. GPS measurements at the reference monuments will allow
analysts to continue to monitor the physical stability of the main
observing monuments and provide additional data for the estimation
of the regional tectonic stability of the area. A footprint survey
of the Fort Davis VLBI and the McDonald SLR site (see Figure 1) was
completed by Bendix Field Engineering Corporation in June; GORF,
GSFC will be occupied this fall for footprint studies. Future footprint
sites include several key sites in California, Westford, MA, Haleakala
and Kokee Park, HI, and selected VLBI sites in Alaska.
The CDDIS will archive GPS data from all types of the applications
described above. Currently, the CDDIS is archiving data in raw, receiver
format as well as the approved Receiver INdependent EXchange (RINEX)
format. A set of tables in the CDDIS ORACLE data base has been created
to track GPS experiment, session, site, and satellite information.
Software has been developed to summarize RINEX-formatted GPS data
and load the data base. CDP investigators can query these tables
by time and location to determine data availability. The data are
temporarily archived on-line to an erasable optical disk for archive
processing. At that time, users can access this data and perform
remote file copies to their home institutions for further analysis.
As more GPS data arrives at CDDIS, older data are archived off-line
to magnetic tape.
GSFC's VLBI Analysis Group, Code 926.9, has recently submitted
a new VLBI analyzed data package to the CDDIS. These results span
the 1979 through 1989 time period and were processed in solutions
GLB656 through GLB660 with the MARK III analysis system. The following
tables contain the data from this submission:
ANTENNAS_VLBIGSFC Radio telescope information
APLOCATIONS_VLBIGSFC Latitude and longitude values for each mobile
and fixed VLBI site
APSTAR_VLBIGSFC Coordinates for observed radio sources from
solution GLB658
BASELINE_VLBIGSFC Length, transverse, and vertical baseline
evolution from solution GLB660
BASELINEMEAN_VLBIGSFC Mean lengths of computed baselines from
solution GLB660
BASELINESLOPE_VLBIGSFC Rates of change of baseline lengths from
solution GLB660
BASELINETRANSVERSE_VLBIGSFC Transverse statistics of baseline components
from solution GLB660
BASELINEVERTICAL_VLBIGSFC Vertical statistics of baseline components
from solution GLB660
EXPERIMENTS_VLBIGSFC List of VLBI experiments and participating
sites
POSITIONS_VLBIGSFC Geocentric site positions by session from
solution GLB660
POSITIONSYR_VLBIGSFC Site positions by year from solution GLB659
ROTATION_VLBIGSFC Earth rotation and nutation results from
solution GLB658
In addition, the site positions and velocities and covariance matrix
from solution GLB659 are stored off-line. More information on these
solutions and the processing techniques can be obtained from the
CDDIS. The data and text associated with this submission will also
be published in the forthcoming NASA document, TM 100765.
In addition, the annual report for 1989 from the IERS containing
the Earth orientation parameters is also on-line in the CDDIS. The
parameters were derived in four solutions:
EOP(IERS) 90 C 01 Earth orientation parameters at 0.05 year
intervals (normal values)
EOP(IERS) 90 C 02 Earth orientation parameters at 5 day
intervals (normal values)
EOP(IERS) 90 C 03 Earth orientation parameters at 1 day
intervals (normal values)
EOP(IERS) 90 C 04 Earth orientation parameters at 1 day year
intervals (smoothed values)
This data set can be listed by querying the CDDIS data base table
ROTATION89_IERS.
This section is designed to give brief notices of special events
or problems encountered in recent months.
In a recent issue of the DIS Bulletin, it was reported that all
Zimmerwald data since 1984 required correction for a time bias of
100 microseconds. This reported time period was incorrect. All epochs
OF 1984 (not SINCE 1984) require this correction. A precursor pulse
in the Zimmerwald timing system created this problem from the beginning
of their operation with a third generation laser in May 1984. This
corrected data has been delivered to the CDDIS and will be available
upon request to the SLR user community.
The CDDIS is now archiving SLR data from the ETALON-I and ETALON-II
satellites in support of the intensive tracking campaign for IERS.
The data will be made available to the general user community on
the regular monthly release tapes. Alternatively, the entire set
of data from the ETALON satellites (starting in February, 1989) is
available upon request.
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