S2 Systems in Geodesy

1. S2 Systems in Geodesy Space Geodynamics Laboratory, CRESTech Geodetic Survey Division, NRCan Dominion Radio Astrophysical Observatory,NRC Canadian Space Agency Presented by: Georg Feil

2. Summary • Space Geodynamics Lab • CGLBI overview & operation • S2 Recording System • S2 Data Acquisition System • S2 experiment setup demo • S3 System Development

3. SGL - Space Geodynamics Laboratory • A division of CRESTech • Centre for Research in Earth and Space Technology • Multidisciplinary research institute located in Toronto, Canada on the campus of York University • Developers of the S2 Recording System and S2 Data Acquisition System • Major collaborators within Canada: • Dominion Radio Astrophysical Observatory, Penticton(S2 Correlator) • Geological Survey Div. of NRCan, Ottawa (CGLBI)

4. CGLBI: Geodetic VLBI for Canada • Environment: • Unique Canadian Geology and size of landmass allow construction of a system with baselines on exposed craton for maximum stability. • Geographic location facilitates links between Europe and East Asia, spanning the Atlantic and Pacific oceans. • Role within the CACS: • CACS = Canadian Active Control System • VLBI provides fiducial sites. • VLBI provides long-term stability.

5. The CGLBI Program International / National Contributions International collaboration through IVS/NEOS/CORE/etc. leading to the IERS and a wider community. (Geophysics/Crustal Dynamics/Earth Orientation) • Determining Earth Orientation Parameters (Algonquin Radio Observatory). • Maintenance of the ITRC and ICRF (ARO and Yellowknife). National / International Contributions National projects providing data for Canada and the international community. (Canadian Active Control System) • ARO and Yellowknife are global fiducial stations as a result of their inclusion in international VLBI experiments. • Other CACS fiducial station positions will be determined using interferometry between the ARO and the CGLBI transportable antenna.

6. S2 CGLBI Validation • The S2 CGLBI network is still considered to be in a validation phase • First CGLBI S2 schedule was run successfully during an experiment in August 1998. • Validation experiments so far have used up to 3 stations • Algonquin • Yellowknife • Transportable antenna (CTVA) now at DRAO

7. CGLBI Validation Network YELL ALGO DRAO

8. Algonquin Radio Observatory • The Algonquin Radio Observatory (ARO) located in Algonquin Provincial Park, Ontario is currently used ~once a week as part of the CORE and NEOS programs using Mark III equipment on long term loan from NASA. • NEOS = National Earth Orientation Service • CORE = Continuous Observations of the Rotation of the Earth. • The GSD operates a permanent ACP at the same site. • The largest and most sensitive regularly participating antenna in the CORE and NEOS programs.

9. Yellowknife Observatory • The 9m diameter antenna located at the Yellowknife Geophysical Observatory (GSC, Pacific Division) on the Canadian Shield takes part in the NAPS VLBI network. • NAPS = North American Plate Stability • The GSD operates a permanent ACP at the same site.

10. Canadian Transportable VLBI Antenna (CTVA) • Transportable 3.6m diameter VLBI antenna • Will be co-located with CACS (GPS) Active Control Points. • Currently located at DRAO in Penticton, B.C.

11. S2 System Validation “Network” Validation Network Considerations: • At the 128 Mbits/sec, ALGO-CTVA is approximately as sensitive as two 16m antennas at 56 Mbits/sec. • YELO-CTVA Scans difficult to obtain. • More stations required to determine Earth Orientation Parameters (and improve Nutation). Other: • Cable-cal not yet available for CTVA. • Meteorological Data at CTVADRAO integrated with PCFS as of December 1999. Available at all Canadian Active Control System (CACS) GPS stations.

12. CGLBI Network Expansion Plans GSD has purchased two new S2 Data Acquisition Systems (expected in April, 2001). These two will be tested within Canada before being sent out on loan to partner antennas (Kokee Park / Fairbanks(?)). CSA has agreed to loan S2-RT to Fairbanks, Kokee has Aus. RT on site. The DASes may then be sent on loan elsewhere in order to broaden the number of global VLBI stations. Simulation results and antenna availability will determine which stations we use. BKG (Germany) has purchased one S2 DAS & RT for use with TIGO which will be located in Chile. The GSD will support TIGO through designing/operating and correlating experiments which utilize this station. The CTVA will remain at DRAO until mid-2001, before being moved to Shirley’s Bay (near Ottawa) on its way to St. John’s, Newfoundland. The next site will likely be near Victoria, British Columbia. We plan to continue to run CGLBI and other S2 sessions through the year utilizing the stations available.

13. The Canadian S2 System:Data Acquisition and Recording • S2 System Concepts: • Modular • Cost-effective • Recording Terminal: • Utilizes commercial video recording (SVHS) technology. • 6 to 8.5 hours continuous recording at 128 Mbits/sec. • Data Acquisition System: • 900 MHz IF bandwidth • Up to 256 MHz baseband BW • Uses a unique Bandwidth Synthesis technique to allow high resolution correlation peak (delay) determination

14. S2 Frequency Switching • The S2 system uses frequency switching to do bandwidth synthesis • LO frequencies switch coherently at rates up to 50 Hz • Maximum settling time 1 ms, maximum phase noise 2 deg rms • Minimizes hardware cost: Only need 2 BBCs • Performance is equivalent to normal “simultaneous-acquisition” systems of comparable BW (e.g. MkIII) • Proper design of switching sequence minimizes error sources • Considerations: • Faster switching reduces bias due to changes in the Ionosphere during switching. • Slower switching reduces data losses due to switching(~2 ms blanking period, or ~20 ms without delay tracking) • Delay tracking reduces data loss caused by geometric delay (~20ms difference in wavefront arrival time) • High switching rates require delay tracking. Require integral # of cycles/day, cycles/scan, seconds/scan

15. S2 Frequency Switching Current frequency switching usage: • Instantaneous bandwidth = 32 MHz, 16MHz in each of two BBCs, 2 bits/sample. • Receivers determine band limits (spanned bandwidth) • A 12-step sequence for each BBC (24 frequency states) 1 8212.99 8932.99 5 8217.99 8927.99 9 2247.99 2332.99 2 2227.99 2352.99 6 8422.99 8722.99 10 8307.99 8837.99 3 8502.99 8642.99 7 2232.99 2347.99 11 2237.99 2342.99 4 2272.99 2307.99 8 8237.99 8907.99 12 8277.99 8867.99 • At 1 Hz switching rate period of entire sequence is 12 sec. Scan durations are set to an integral multiple of this period. • Correlator data blanking between switches is currently set to 30ms (no delay tracking yet), a 3% loss of data or a 1.5% SNR reduction. This blanking time will be significantly reduced (an order of magnitude) when delay tracking is implemented.

16. S2 Validation: Operations S2 Recording Terminal (RT) Usage • Fully supported by the PCFS. • Power On Self Test • Status Monitoring and Control Via Console (or ethernet). • A proven system with an extensive track record. S2 Cassette Tapes and Cassette Changes • High quality reusable SVHS cassette tapes, used in sets of 8. • Cassette changes at stations are given 4 minutes in the schedule. Very simple. • Cassettes cost approx. C$12.50 (US$8.50) each. 32-48 used per station per 24 hr experiment (4-6 sets of 8 cassettes) depending on speed/mode. • Typical tape cost per 24 hours = $272 [1.4 Terabytes]

17. S2 Validation: Operations S2 Data Acquisition System (DAS) Usage • Not yet supported by the PCFS. Mode setup and loading of frequency sequence from PCFS partially implemented by GSD. • Status Monitoring and Control via console (or ethernet). • Power On Self Test • AGC sets gains and sampler thresholds precisely • Phase cal extraction/monitoring (tone detect).

18. S2 Validation: Scheduling Notes • Cassette handling is significantly different from Mk-III tapes (no rewinding). Tapes only go forward so easy to recover from failures • SKED doesn’t support S2 • SCHED (Astronomical Scheduling s/w) officially supports S2 recorder. • DRUDG officially supports S2 recorder • In 1999 used a locally modified version of SKED (tape handling changes) to export a list of scans (sources, times) into SCHED. No S2 DAS commands in schedules (none required after mode is set and sequence started, with delay tracking will require source change commands)

19. The Canadian S2 Correlator • Developed at DRAO with funding from the Canadian Space Agency to supportSpace VLBI (astronomy). • In operation for more than three years. • 6 station configuration (expandable to 10+) • Has 6 S2 playback terminals • Designed to handle S2 frequency-switched bandwidth synthesis data. • Extensive Data Quality Analysis

20. Analysis of CGLBIExperiments • Correlator output is in UVFITS format. • The UVFITS file is processed to create an output file in the CGLBI format (simple text not unlike the NGS format). • A program called “CGLBIDB” is used to convert the CGLBI file into a CALC/SOLVE database. • Capability to analyze VLBI data was re-established at GSD in 1998. Software modifications for frequency-switched CGLBI data were completed in 1999. • Work to track recent CALC/SOLVE updates continues (Calvin Klatt)

21. Past Validation Experiments • 10 Experiments conducted in 1998-1999 • five 24-hour geodetic databases produced. • 18 Experiments conducted in 2000 • eight 24-hour geodetic databases produced • Experiments continue (one is scheduled for next week)

22. Experiment Results • Analysis parameterization: • Apriori EOPs via flyby files (last.erp from GSFC). • Relatively few parameters used (no improvements seen from shorter clocks or tropo gradients). • Analysis: • Baseline length repeatability better than error bars suggest. • Scatter in XYZ/UEN position a bit larger than expected… EOPs? • Small difference from ITRF97: Reasonable?

23. Validation Operations Experiments

24. Validation Operations Experiments

25. Validation Operations Experiments

26. Validation Operations Experiments

27. S2 DAS/RT Operation

28. S2 DAS/RT Operation Demo of • Experiment setup & operation at an observatory • Typical pre-experiment checks

29. Demo test setup 5 MHz Signal Gen.505 MHz IF1 C1 Cable

30. S2 DAS/RTExperiment Setup Start of experiment • Configure DAS • Set mode (32x4-2-U) • Set IF atten and ensure AGC is on • Start frequency switching • For delay tracking: set time, set source coords on each change • Configure S2-RT • Set mode (32x4-2) • Set tape ID & user info fields • Done automatically via schedule/PCFS

31. Example S2 DAS console display

32. Example S2-RT console display

33. S2 DAS/RTPre-experiment Checkout • DAS and RT Console displays • Pre-experiment checks • Power-on self test • “Post-ship” test • Signal path checks (analog & digital) • TPI, tone detect

34. S2 DAS tone detect screen

35. S3 System Development

36. S3 System Development • S3 Recorder builds on the Transport Array concept established by the S2 • Uses D9 (formerly Digital-S) digital video transports by JVC • Also D9-HD = Double-rate JVC D9 transport • Modular architecture • Achieves compatibility with future video or data drives through replacement of Storage Module Interface (SMI) PCI cards • Extensive use of off-the-shelf components

37. S3 System Development • Specification Summary • Total data rate 1 Gbit/s or 2 Gbit/s (S3-E) with eight transports • 30 hours unattended recording time at 2 Gbit/s with COTS robotic tape changer • Low tape cost $140 US/hour at 1 Gbit/s • Tape “burn rate”: 76 tapes/24 hrs (1 Gbit/s) • 9 or 10 sets of eight tapes • Data capacity • 140 GBytes per DS124 tape • 215 TBytes in Tape Changer rack (192 tapes) • VSI (VLBI Standard Interface) compatible

38. S3 Development Status • Prototype FDRD (signal channel card) being debugged • Transport modifications and TCP software under development

39. More Information? • CRESTech/SGL Web Site: www.sgl.crestech.ca • These slides available at ftp://ftp.sgl.crestech.ca/pub/s2/doc/appnotes/tow5.ppt • CGLBI Web Site http://www.sgl.crestech.ca/cglbi • Information on Algonquin, Yellowknife and the transportable (CTVA) observatories. • Analysis of VLBI data • Scheduling of VLBI experiments • GSD Web Site http://www.geod.nrcan.gc.ca/index.html • Canadian Spatial Reference System (CSRS) • Canadian Active Control System (CACS) • International VLBI Service for Astrometry and Geodesy Web Site http://ivscc.gsfc.nasa.gov/ivs.html • Thanks to Calvin Klatt at GSD for many of these slides