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The VLBI2010 Broadband System: First Geodetic Results

The VLBI2010 Broadband System: First Geodetic Results. Reported by Arthur Niell MIT Haystack Observatory. 1. GGAO12M Development Team.

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The VLBI2010 Broadband System: First Geodetic Results

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  1. The VLBI2010 Broadband System:First Geodetic Results Reported by Arthur Niell MIT Haystack Observatory IVTW - Haystack 1

  2. GGAO12M Development Team Chris Beaudoin 1 , Bruce Whittier1, Mike Titus1, Jason SooHoo1, Dan Smythe1, Chet Ruszczyk 1, Alan Rogers1, Mike Poirier1, Arthur Niell1, Russ McWhirter 1, Alan Hinton1, Brian Corey1, Jon Byford, Alan Whitney 1 Chopo Ma 2 Ed Himwich3, Tom Clark3 Jay Redmond4, Skip Gordon4, Mark Evangelista4, Irv Diegel4, Paul Christopolous 3 Wendy Avelar 5, Chuck Kodak5, Roger Allshouse 5, Katie Pazamickas 5, Ricky Figueroa5 1 MIT Haystack Observatory, 2 NASA GSFC, 3 GSFC/NVI ,4 HTSI, 5 ITT IVTW - Haystack

  3. Background IVTW - Haystack • Science driver • Accurate terrestrial and celestial reference frames • 1 mm position and 0.1 mm/yr velocity • Requirement for accurate sea level determination • Achieved by combination of VLBI, SLR, and GNSS • Next generation VLBI development • Fast slewing antennas to rapidly sample the atmosphere • High precision delay observable • Wide spanned bandwidth: 2 – 14 GHz • Four bands and two polarizations • High data rate: 8 Gbps

  4. 12m antenna at Goddard Geophysical and Astronomical Observatory, Greenbelt, Maryland IVTW - Haystack

  5. Observing Frequency Bands Phase ~ 2.2 – 15 GHz Spanned RF Bandwidth OLD 2 Frequency (GHz) 14 IVTW - Haystack 5

  6. Feed and LNAs cooled to ~20K Both senses of linear polarization used RF filter phase/noise cal Antenna Control room Odd channels from each pol’n for one band output to each Mk5C. 2 Gigabits/sec recorded on each Mk5C. Total data rate: 8 Gbps IVTW - Haystack

  7. Caltech supplied QRFH feed 2-12 GHz LNAs IVTW - Haystack

  8. Westford QRFH feed IVTW - Haystack

  9. Broadband 8 Gbps Rack IVTW - Haystack • All backend equipment in one rack • Picture (oops! DBE compatibility test in progress)

  10. GGAO12M SEFD - 2012 May IVTW - Haystack

  11. Signal Chain Frontend IVTW - Haystack • Dewar (~20K) • QRFH feed • Two broadband LNAs • Couplers for phase and noise cal injection • Phase cal • 5 MHz spacing • Use all tones for each channel to obtain delay correction • Noise source for Tsys • 80 Hz switching controlled by RDBE • Not implemented for these observations • RF to control room over optical fiber • Caused implementation delay because manufacturer did not meet advertised specs

  12. Signal Chain Backend IVTW - Haystack • UpDown Converter • Select frequencies and Nyquist zone (NZ2 used) • Band frequencies (lower edge) • 3.2 GHz, 5.3 GHz, 6.3 GHz, 9.3 GHz • Band width 512 MHz • RDBE • Joint NRAO-Haystack development (also in use at VLBA) • PFB: 32 MHz channels (sub-bands) • Record eight horizontal and eight vertical polarization channels • 2 Gbps data rate • Mark5C recorder • 2 Gbps • 1 module

  13. Geodetic Session Components IVTW - Haystack • Schedule using sked(simplified) • Select sources, band frequencies, SNR target per band • Specify scan parameters and antenna characteristics • Push GO to generate 24 hour schedule • Observing • Convert sked output to scripts for controlling RDBEs and Mark5Cs • Make usual checks of frequencies and time (but four sets!) • Antenna is run by Field System • RDBEs and Mark5Cs are run from scripts until Field System ready • Quantization threshold set for each scan by script

  14. Geodetic Session Components IVTW - Haystack • Correlation and observable estimation • DiFX • Difx2mark4 • fourfit • coherent fit to 4 bands*2 polarizations + ionosphere • Geodetic estimation • nuSolve with stochastic processes for atmosphere and clocks

  15. Results IVTW - Haystack • 2012 May six hour session • 30 scans/hour 30 second scans • 50 source s ≥ 0.6 Jy • Median formal delay error ~0.5 psec • Scaled delay error ~3 psec (1 mm) • Position estimation for GGAO12M • Delay residual RMS using νSolve 10 psec • Position uncertainties ~ 2/3/9 mm in E/N/U • Probably atmosphere dominated • Phase cal delay variation in azimuth of 4 psec • Possible 0.5 mm horizontal position error

  16. IVTW - Haystack

  17. IVTW - Haystack

  18. RFI IVTW - Haystack • External sources of RFI • Usual S-band sources • Unknown 4 GHz at GGAO (NSA or CIA?) • Local comm link at 6 GHz at Westford • Intra-technique RFI for geodetic Core Sites • Satellite Laser Ranging aircraft avoidance radar at 9.4 Ghz • Potential to damage LNAs • Must keep pointing direction 90º apart • Coordinated observing appears difficult • Attempting to mitigate by physical blockage near radar • DORIS transmission near 2 GHz

  19. Sky coverage no mask IVTW - Haystack

  20. Sky coverage mask on IVTW - Haystack

  21. Results IVTW - Haystack • 2012 October 4-5 • Two six hour sessions • 34 scans/hour 30 second scans • SLR radar active on Oct 4; mask on • SLR radar off on Oct 5; mask off • Fringes both days • Both days correlated on Mark4; only three phase cal tones/channel • No post-correlation processing will be done till correlated on DiFX • Anxiously awaiting results to look at baseline repeatability

  22. Next steps IVTW - Haystack • 12m antenna • Install motorized positioner for Dewar/feed/LNA package • Implement noise cal for Tsys • Signal chain • Replace 4 RDBEs by 2 quad-RDBEs (4 IFs per ROACH) • Replace 4 Mark5Cs by one Mark 6

  23. Summary IVTW - Haystack • Broadband system • Successful implementation on the 12m antenna • Broadband RF from 2 – 12 GHz achieved with QRFH and two LNAs • Obtained anticipated sensitivity of 2500 Jy for SEFD • Phase calibration allows phase connection over full range of frequency • Obtained anticipated delay precision of less than 4 picoseconds • Operations • UDC/RDBE/Mark5Cs operated remotely • Geodetic sessions run unattended after setup • Correlation/post-processing • DiFX correlation • Coherent fitting of four bands dual polarization with ionosphere estimation • Full end-to-end geodetic observations

  24. Courtesy Wendy Avelar IVTW - Haystack

  25. IVTW - Haystack

  26. IVTW - Haystack

  27. Signal chain development IVTW - Haystack • RDBE-Q • Input four 512 MHz IFs • Output 2 x 2 Gbps (current geodesy mode) or 2 x 4 Gbps • Output in VDIF with complex samples • Tested with test vector generator and test tone inputs • Mark6 • 8 Gbps to one module (now) • Anticipate first observations in December • RDBE-X • Design begun (Haystack and Petrachenko) • ROACH2 based • Four 1 GHz IFs • 16 Gbps

  28. Haystack-NASA VGOS Systems IVTW - Haystack • GGAO12M • Elevation motion – problem has not returned • Phase cal peculiarities – most of system to be replaced • Positioner • Moves under motor control • Dewar holds vacuum • Testing for cooling right now • Install on 12m mid-November • Westford • QRFH feed and new hardware in Dewar performed well • Tsys ~ 30K • Efficiency very low

  29. Other VGOS development IVTW - Haystack • Kokee 20m • Haystack will install signal chain by next summer if observing permits • Kazan • Proposal for 12m with Broadband Signal Chain submitted by HTSI and Haystack • Too expensive, so fall back to Intertronics S/X feed and LNAs • Receiver and formatter/recorder not discussed yet • USNO • Expect RFP within a month for 12m at Kokee • NASA Request for Information (RfI) for Core Sites (up to 10) • Response by HTSI/Haystack for combined VLBI/SLR/GPS/DORIS • Separate response by Haystack to provide VLBI system

  30. Geodetic VLBI Highlights VLBI2010 broadband system at GSFC 12m antenna with all major components First geodetic session scheduled, observed, and correlated DiFX correlator and fourfit Developing new capabilities for broadband operation Coherent fitting across polarizations and bands Correlation of mixed channel widths , e.g. 8 MHz/32MHz Mark6 recorder 16 Gbps will reduce four recorders to one Kazan University VLBI2010 signal chain (proposed) May be second operational system Cooperative development with HTSI (Honeywell) IVTW - Haystack

  31. Program Overview NASA (2010-2014) Engineering Operations Research and development Technique improvement/science USNO correlator (2009-2012 (2013 likely)) Engineering and development Operations backup USNO VLBI2010 implementation (-2012) VLBI2010 signal chain for Kokee 20m antenna Kazan University VLBI2010 signal chain (proposed) Sub-contract to HTSI for 12m antenna IVTW - Haystack

  32. NASA Contract Engineering support Field station diagnostics and repair Analyse station performance from correlator results Respond to problems from stations Maintain spares depot; repair modules; ship replacements Develop replacement equipment Correlator development (Mark4 and DiFX) Operations Mark4 and DiFX correlators R&D and Reference Frame sessions New broadband data Westford antenna GGAO12M Other sites as needed IVTW - Haystack

  33. NASA Contract (cont’d) Research and development Frontends (Cryogenic feeds and amplifiers) Receivers (RF to video) Digital backends Recorders VLBI2010 broadband system 12m antenna at Goddard Space Flight Center Broadband system on Westford Technique improvement and science RFI mitigation Observation planning Atmosphere Radio astronomy ‘effects’ IVTW - Haystack

  34. Other Active Contracts USNO: Washington Correlator engineering support through 2013 probably Maintenance of Mark4 hardware correlator Haystack correlator as backup USNO: VLBI2010 signal chain implementation UpDown converters, RDBEs, and Mark5Cs – 1st contract Dewar/feed/LNAs/calibration box, optical fiber links – current Installation on Kokee 20m antenna IVTW - Haystack

  35. Potential Contracts (cont’d) Kazan University (Russia) VLBI2010 system (proposed) Will be under a contract from HTSI New 12m to be purchased from Intertronics Antennas HTSI (Honeywell) responsible for everything else Haystack to provide the broadband signal chain and checkout of geodetic VLBI functionality, first in US then in Russia Moscow State University (Russia) VLBI2010 systems HTSI: same arrangement Proposal under discussion GSI (Japan) Interest in obtaining front end (Dewar/LNAs/feed) Others interested in VLBI2010 Signal Chain Norway, Sweden, Spain/Azores/Canary Islands IVTW - Haystack

  36. NASA Geodesy and Haystack Motivation for new system development (IVS WG3) Replace aging antennas Improve accuracy to 1 mm Provide for continuous, unattended operation Resulted in VLBI2010 specifications Background for Haystack involvement Provided majority of data acquisition systems for global program Significant contributions to atmosphere and astronomy modeling IVTW - Haystack

  37. ftp://ivscc.gsfc.nasa.gov/pub/misc/V2C/TM-2009-214180.pdf http://ivscc.gsfc.nasa.gov/about/wg/wg3/ IVS_WG3_report_050916.pdf IVTW - Haystack

  38. VLBI2010 development IVTW - Haystack • Limiting error sources • Varying atmosphere delay • Sensitivity • Strategy • Use fast-slewing antennas (5º/sec-12º/sec slew rate) • Obtain delay sensitivity through high data rate and wide spanned bandwidth (Broadband Delay) • Design goals • Antennas of ≥ 12m diameter • Data rates ≥ 8 Gbps using four bands of 0.5 GHz to 1 GHz each • Spanned bandwidth 2.2 GHz to ~14 GHz: delay uncertainty ~4 psec • BUT maintain observing compatibility with current S/X systems

  39. VLBI2010 signal chain Cooled broadband QRFH feed and LNAs Purchased from Caltech Tested and packaged by Haystack Phase and noise calibration Phase cal generator developed by Haystack Packaged by HTSI UpDown Converters (4) (Haystack) In use for 2-12 GHz Possible extension to 2-14 GHz (or higher) IVTW - Haystack

  40. VLBI2010 signal chain RDBE digital back end (4) Developed by NRAO and Haystack Produced by Digicom (California) In use by VLBA and NASA Mark5C recorder (4) (Conduant) In use by VLBA and NASA In use by EVN Mark6 recorder (1) (Conduant) Up to 16 Gbps from four 4 Gbps inputs Will replace 4 Mark5C recorders IVTW - Haystack

  41. VLBI2010 correlation/processing Correlation on DiFX software correlator Four separate correlations (four bands) Working on 8MHz within 32MHz correlation for compatibility with legacy S/X systems Post-correlation processing difx2mark4 – convert native output to Mark4 input fourfit Coherent fit across bands and polarizations while estimating ionosphere IVTW - Haystack

  42. VLBI2010 Status 12m system Operational at Goddard Space Flight Center Using deliverable equipment Some components not tested or not implemented First geodetic observing session just completed Westford Using deliverable equipment Low efficiency (≤ 20%) above 5 GHz not understood Kokee 20m Most of signal chain completed Funding/mechanism for mounting Dewar unclear IVTW - Haystack

  43. NASA Space Geodesy Project (SGP) Project level at NASA Headquarters Viewed within NASA HQ as best way to get support and funding Planning for ten sites Not all in North America Haystack involvement Short term requirements Complete and document 12m broadband system Potential role of Haystack in SGP future Not known at this time Role of Haystack outside of SGP Expected to continue as currently defined IVTW - Haystack

  44. Current Technical Development Mark6 RDBE RDBE-Q (four 512-MHz bands per ROACH) RDBE-V (two 1-GHz bands per ROACH) Future: four 1-GHz bands per ROACH MCI (complete monitor and control) RFI mitigation Vector Tie System High speed networking (real-time and e-xfr) IVTW - Haystack

  45. Technique Improvement Implement end-to-end scheduling/analysis capability Develop improved atmosphere modeling Study effect of radio source structure Analysis, modeling, and delay correction IVTW - Haystack

  46. IVTW - Haystack

  47. Astro/Geo Common Dev’ment Shared goals (simplified) Improve sensitivity Increase data storage capacity Differences Astronomy –higher frequency for better angular resolution Geodesy – wider spanned bandwidth for better delay sensitivity Astronomy – campaign observing few times per year, several antennas Geodesy – sustained observing several times per week, many antennas Astronomy – mobilize personnel & equipment for limited time with close to best possible capability Geodesy – operational reliability through less than best achievable performance IVTW - Haystack

  48. VLBI geodesy IVTW - Haystack • Unique measurements by VLBI • Earth rotation angle (time): UT1-UTC (keep GPS up) • Scale of terrestrial reference frame: sea level change • Nutation: (e.g.) dynamics of the Earth’s core • Mandate to NASA for accuracy improvement • National Research Council decadal survey • 1 mm position and 0.1 mm/year velocities • Implementation proposed through Space Geodesy Project • VLBI, SLR, GPS, and DORIS • Unified station • Vector ties among techniques to 0.1 mm

  49. VLBI2010 IVTW - Haystack • Observations • One or two scans per minute scattered around the sky • Scan lengths only long enough to get necessary SNR • Duty cycle only about 1/3 so can use burst mode to maximize instantaneous data rate.

  50. VLBI2010 System IVTW - Haystack • Antenna and data acquisition • Cooled broadband frontend 2 – 14 GHz • Flexible RF to IF frequency conversion • Digital backends • High data rate recorder(s) • DiFX software correlator • Extract all phase-cal tones • Correlate 8 GHz S/X legacy data and 32 MHz broadband channels • Post-correlation • Coherent fitting of all polarizations • Estimate differential ionosphere

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