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CDDIS Bulletin - August 1993
Volume 8 No. 6
In this issue:
About the cover: The map on the cover of this issue of the CDDIS Bulletin shows the current and planned international VLBI network. This network will consist of 54 VLBI stations by 1995. The new stations will be implemented by various global agencies.
A majority of the fax numbers at GSFC will change on October 1, 1993. Below is a list of old and new numbers for many of the Space Geodesy Program contacts at GSFC.
Group/Name Location Old Number New Number
Space Geodesy Program/GSFC (Code 920) Bldg. 28 301-286-4943 301-286-1776
Space Geodesy and Altimetry Project Office (Code 920.1) Bldg. 28 301-286-4943 301-286-1776
Laboratory for Terrestrial Physics (Code 920) Bldg. 22 301-286-9200 301-286-1757
Geodynamics Branch (Code 921) Bldg. 22 301-286-1616 No change
Space Geodesy Branch (Code 926) Bldg. 22 301-286-2562 301-286-1760
Earth Sciences Directorate Office (Code 900) Bldg. 16 301-286-3884 301-286-1738
1992 was a very good year for the SLR user community. Data production increased by nearly 100% due to new satellites (TOPEX/POSEIDON, LAGEOS-II), new sites (Evpatoria, Ukraine; Komsomolosk-na-Amure and Balkhash, Russia; and the second station at Maidanak, Uzbekistan) and the addition of a second shift at many of the NASA SLR sites. Table 1 on the following page details pass and point totals by station for 1992. All but 5% of the total passes and 1% of the total points have been released to the SLR user community (the B version of all months has been released from the CDDIS).
Normal points generated from SLR full-rate data are available from the CDDIS for electronic file transfer. These files are stored by month, version, and satellite and are located in the directory DIS_DATA:[SLRDATA]. Users interested in retrieving these files electronically should contact the CDDIS staff to obtain username and password information. We encourage data users to retrieve these files via electronic means to save money and time in the generation and mailing of data tapes.
One more item of interest, AlliedSignal Technical Services (ATSC) will soon be supplying normal points generated from TOPEX/POSEIDON full-rate data to the CDDIS. These data have been delayed by software enhancements required to generate the normal points. The normal points will be generated with the appropriate center of array correction. However, in order to conform to the MERIT II format, the correction will be removed in the final product.
Dr. Richard Gross has recently submitted his SPACE92 data set. These data are combined Earth orientation data generated from space geodetic observations spanning 1976 through 1992. The techniques used include VLBI, SLR, LLR, and GPS. The data, as well as a textual description of the processing, are available on-line from the CDDIS via ANONYMOUS FTP in the directory ANON_DIR:[JPL]; the name of the file is SPACE92.
Data from three 1992 and 1993 footprint experiments have been delivered to the CDDIS. Users interested in obtaining data from any of these experiments should contact the CDDIS staff.
Mojave. In the June 1992 issue of the CDDIS Bulletin, it was announced that data from the second epoch GPS survey in Mojave, CA was received and archived in the CDDIS. This experiment was part of Meghan Miller's investigation at Central Washington University; the author regrets not crediting the investigator in the initial article.
Ft. Davis/McDonald. The data from the second epoch of the Ft. Davis/McDonald Texas footprint has been made available to the CDDIS by the University of Texas. This GPS experiment was performed May 17 through 21, 1992. The first epoch experiment at Ft. Davis/McDonald was performed in June 1990; five markers were observed during both experiments. The data are currently available in raw Trimble receiver format and consist of 122 files totaling 19.5 Mbytes in size; message, ion, and ephemeris files are also included. Log sheets, in hardcopy format, are also available.
Easter Island. AlliedSignal Technical Services Corporation (ATSC) recently completed a footprint at Easter Island, Chile. This survey also included the monument which will be the location of the permanent GPS tracking site at Easter Island. The data are currently available in both raw Trimble receiver format and RINEX format. The raw data consist of 124 files totaling 16.65 Mbytes in size; data in RINEX format consist of 70 files totaling 12.4 Mbytes in size. Log sheets, in hardcopy format, are also available.
Santiago. A footprint at Santiago, Chile was also conducted by ATSC in May 1993. This survey included the mobile SLR monument. The data are currently available in both raw Trimble receiver format and RINEX format. The raw data consist of 92 files totaling nearly 12 Mbytes in size; data in RINEX format consist of 52 files totaling nearly 9 Mbytes in size. Log sheets, in hardcopy format, are also available.
Footprint Site Start Date End Date No. Sites SLR/VLBI/GPS Markers Occupied
Fort Davis, TX 17-May-92 21-May-92 8 7850 (mobile VLBI and SLR)
Easter Island, Chile 26-Apr-93 01-May-93 4 4008 (future fixed GPS)
Santiago, Chile 09-May-93 14-May-93 4 7400 (mobile SLR)
On July 30, 1993, the AlliedSignal Technical Services Corporation SLR Group will move to a new location down the road from the Aerospace Building. A letter will be sent out shortly by ATSC to inform the community of their new location and new phone numbers.
To date, the CDDIS has archived over eleven Gbytes of global GPS tracking data for the IGS and FLINN. Since the June 1993 issue of the Bulletin, the CDDIS has archived data from the following new GPS tracking sites:
Mon.
Name Site Name Data Source Receiver Start Date End Date
FORT Fortaleza, Brazil CIGNET Rogue SNR-8000 18-Jul-93 -
JOZE Jozefoslaw, Poland Warsaw Trimble 4000 SSE 03-Aug-93 -
KIRU Kiruna, Sweden ESA Rogue SNR-8100 08-Jul-93 -
KOD1 Kodiak, AK NASA/JPL Rogue SNR-8000 09-Jun-93 -
MATH* Lake Mathews, CA SIO Trimble 4000 SST 16-May-93 -
MDO1 McDonald Observatory, TX NASA/JPL Rogue SNR-8000 03-Jun-93 -
PVEP* Palos Verdes, CA SIO Trimble 4000 SST 19-May-93 -
RCM4 Richmond, FL (new location) CIGNET Rogue SNR-8000 16-Jul-93 -
WUHN Wuhan, PeopleUs Republic of China CIGNET MiniMac 2816AT 07-Apr-93 23-Jun-93
The sites denoted by an * are part of the PGGA operated by the Scripps Institution of Oceanography. Additional data from Wuhan may be supplied by CIGNET in the future.
This section is designed to give brief notices of special events, new data sets, or problems encountered in recent months. The CDDIS staff believes the user community should be informed of any data problems in order to ensure that the best results possible are produced from data issued by the archive.
The CDDIS has recently received floppy disks containing SLR full-rate data from the laser station at Wuhan, Peoples Republic of China (monument number 7236). A total of 243 passes from LAGEOS-I and -II, TOPEX/POSEIDON, ERS-1, STARLETTE, and AJISAI for 1992 were received. These data will be released to the user community in the next few months.
AlliedSignal Technical Services Corporation (ATSC) has recently discovered that all previously-released LAGEOS-II normal points generated from full-rate data (October 1992 through February 1993 ) must be recalled and replaced due to an error in their generic normal point software system. The bin size was not explicitly specified for LAGEOS-II in the processing software, so 30 seconds was used as a default. This value led to array boundary problems and thus caused erroneous normal points (i.e., measurements with redundant time tags, negative standard deviations, etc.) to be produced. However, on-site LAGEOS-II normal point data from the NASA network of sites for these months have been computed correctly since they were generated as part of operational data processing; the bin size indicator in the operational data processing software is set correctly to two minutes. ATSC has regenerated the monthly global LAGEOS-II normal point data sets for October 1992 through February 1993 and these data are now available from the CDDIS.
In the last issue of the CDDIS Bulletin, a table was presented listing SLR systems and their wavelengths. Since this publication, additional information, as well as corrections, have been received; the updates are shown in Table 2 below.
Table 2. SLR System Wavelength Values
Sys.
ID System Name Current System Location Wave-Length Comments
20 CUBLAS Santiago de Cuba 6943 Prior to June 1993
20 CUBLAS Santiago de Cuba 5321 New laser installed June 1993
39 GDRLAS Potsdam, Germany 6943 Station 1181
51 MDNLAS Maidanak, Uzbekistan 5321 Station 1863
54 MD2LAS Maidanak, Uzbekistan 5321 Station 1864
59 KOMLAS Komsomolosk-na-Amure, Russia 5321
60 BALLAS Balkhash, Russia 5321
The MOBLAS-2 system was upgraded from a one to a five pulses-per-second system in June 1992. However, there was a hardware wiring problem in the laser fire (transmit delay) electronics, which was identified and corrected on March 11, 1993. The magnitude of this error was approximately 620 microseconds. This time bias problem affected both quick-look and full-rate data. There were also real time problems in recording the raw full-rate data at five pulses per second, which made some of the full-rate data unrecoverable. This real-time recording problem has improved, but it continues to be investigated by station personnel.
On June 30, 1993, the MOBLAS-2 calibration target was re-surveyed. The calibration distance measured was 2149.316 meters. The previous June 1990 surveyed distance was 2149.300 meters (a difference of 16 mm). Based on specialized orbital analysis by Hughes-STX analysts and conversations with the onsite personnel about the historical stability of the target, the June 1993 calibration distance can be backdated to June 1990. To further complicate issues, the onsite calibration range being used for quick-look processing was 2149.228 (a difference of 88 mm and 72 mm) from the 1993 and 1990 surveys, respectively).
In addition, during the June 1992 through June 1993 time period, the cesium station clock was drifting at a very high rate. This drift rate is modeled during full-rate data processing but not during quick-look processing, thus explaining the slight differences between the time bias corrections in Tables 3 and 4. The variance in the station clock offsets noted in Table 3 below were applied to the full-rate data but not to the quick-look data.
Since some of the full-rate data during 1992 and 1993 are unrecoverable and due to significant data processing differences between quick-look and full-rate data processing, the two tables below are being provided to allow analysts to correct both quick-look data and full-rate data. Neither the full-rate or quick-look data will be corrected and resupplied by ATSC Data Services.
Usage Note: To correct for the range bias, the user should add the range bias correction to the one-way range. To correct for the time bias, the user should add the appropriate time bias correction to the time tag.
Table 3. Range and Time Bias Corrections to MOBLAS-2 Full-Rate Data
Time Span Range Bias Time Bias
From To (mm) (ms) Comments
06/01/90 05/31/92 16 0 2149.316 to 2149.300 meters
06/01/92 03/10/93 16 620 time bias correction good to only 20 5s
03/11/93 06/29/93 16 0 transmit delay wiring problem repaired
06/30/93 present 0 0 2149.300 m target range used
Table 4. Range and Time Bias Corrections to MOBLAS-2 Quick-Look Data
Time Span Range Bias Time Bias
From To (mm) (ms) Comments
06/01/90 05/31/92 88 0 2149.316 to 2149.228 meters
06/01/92 11/09/92 88 620 time bias correction good to only 20 ms
11/10/92 11/21/92 88 619 time bias correction good to only 20 ms
11/22/92 11/25/92 88 618 time bias correction good to only 20 ms
11/26/92 11/28/92 88 617 time bias correction good to only 20 ms
11/29/92 11/30/92 88 616 time bias correction good to only 20 ms
12/01/92 12/03/92 88 615 time bias correction good to only 20 ms
12/04/92 12/06/92 88 614 time bias correction good to only 20 ms
12/07/92 12/09/92 88 613 time bias correction good to only 20 ms
12/10/92 12/12/92 88 612 time bias correction good to only 20 ms
12/13/92 12/15/92 88 611 time bias correction good to only 20 ms
12/16/92 12/18/92 88 610 time bias correction good to only 20 ms
12/19/92 12/21/92 88 609 time bias correction good to only 20 ms
12/22/92 12/23/92 88 608 time bias correction good to only 20 ms
12/24/92 12/27/92 88 607 time bias correction good to only 20 ms
12/28/92 12/30/92 88 606 time bias correction good to only 20 ms
12/31/92 01/02/93 88 605 time bias correction good to only 20 ms
01/03/93 01/05/93 88 604 time bias correction good to only 20 ms
01/06/93 01/08/93 88 603 time bias correction good to only 20 ms
01/09/93 01/11/93 88 602 time bias correction good to only 20 ms
01/12/93 01/15/93 88 601 time bias correction good to only 20 ms
01/16/93 01/19/93 88 600 time bias correction good to only 20 ms
01/20/93 01/22/93 88 599 time bias correction good to only 20 ms
01/23/93 01/26/93 88 598 time bias correction good to only 20 ms
01/27/93 01/29/93 88 597 time bias correction good to only 20 ms
01/30/93 02/02/93 88 596 time bias correction good to only 20 ms
02/03/93 02/06/93 88 595 time bias correction good to only 20 ms
02/07/93 02/08/93 88 594 time bias correction good to only 20 ms
02/09/93 02/09/93 88 593 time bias correction good to only 20 ms
02/10/93 02/12/93 88 622 time bias correction good to only 20 ms
02/13/93 02/15/93 88 621 time bias correction good to only 20 ms
02/16/93 02/18/93 88 620 time bias correction good to only 20 ms
02/19/93 02/21/93 88 619 time bias correction good to only 20 ms
02/22/93 02/24/93 88 618 time bias correction good to only 20 ms
02/25/93 02/27/93 88 617 time bias correction good to only 20 ms
02/28/93 03/03/93 88 616 time bias correction good to only 20 ms
03/04/93 03/06/93 88 615 time bias correction good to only 20 ms
03/07/93 03/10/93 88 614 time bias correction good to only 20 ms
03/11/93 03/12/93 88 -7 transmit delay wiring problem repaired
03/13/93 03/14/93 88 -8
03/15/93 03/16/93 88 -9
03/17/93 03/19/93 88 -10
03/20/93 03/28/93 88 -11
03/29/93 04/04/93 88 -12
04/05/93 04/16/93 88 -13
04/17/93 04/28/93 88 -14
04/29/93 hardware problems, biases unrecoverable
04/30/93 05/05/93 88 -14
05/06/93 05/12/93 88 -15
05/13/93 05/24/93 88 -16
05/25/93 05/28/93 88 -17
05/29/93 06/08/93 88 -18
06/09/93 06/14/93 88 0 station clock resynchronized with USNO;
clock drift stabilized
06/15/93 07/28/93 16 0 target range updated (2149.316 to 2149.300 m)
07/29/93 present 0 0 2149.316 m target range used
ATSC Data Services Group reports that from November 01, 1983 to May 26, 1986 data from the SAO-2 system at Arequipa (station number 7907) was biased short by approximately 7 cm +/- 1 cm. This error was due to an outdated calibration range of 4 cm used in data processing as well as a calibration problem (signal strength). Data from May 27, 1986 through June 17, 1988 was also biased short by 3 cm +/- 1 cm due to the calibration problem (signal strength). To correct for the biases, the user should add the appropriate correction to the one-way range.
ATSC also reports that TLRS-2 data from the 1987 occupation of Huahine, French Polynesia (July 14 to October 08) was biased short by 3 cm due to a survey reduction error (a 3 cm cube constant was not added. To correct for this bias, the user should add 3 cm to the one way range.
Concerning the HOLLAS facility in Mt. Haleakala, HI, ATSC warns that on-site normal point data taken from May 14 through June 8, 1993 should not be used by analysts. A drifting cesium clock at the station was erratic up to nine ms per day. All SLR full-rate data for this time period will be withheld from release. The problem with the clock has been corrected by replacement of the cesium on June 9, 1993.
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