First results of the FAST-S/X-sessions with new VGOS antennasAlexander Neidhardt1, Pablo de Vicente2, Alessandra Bertarini3, Thomas Artz3, Dmitry Ivanov6, Alexey Melnikov6, Johannes Böhm4, Andreas Hellerschmied4,

David Mayer4, Christian Plötz5, Gerhard Kronschnabl5, Axel Nothnagel2, Sergei Kurdubov6 , Andrey Mikhailov6, Dmitry Marshalov6, Ilia Bezrukov6, Yu. Bondarenko6

(1FESG Wettzell, 2Observatorio de Yebes-IGN, 3IGG Bonn, 4Technische Universität Wien, 5BKG Wettzell, 6Institute of Applied Astronomy RAS)

Abstract:The performance of first international observations with new VGOS antennas using the fast slewing mode was decided during the VTC meeting at Ponta Delgada, Portugal. The goal is to observe S/X-schedulesregularly using the fast slewing capabilities of the antennas as long as they are equipped with classic or compatible S/X-capabilities. Two sessions, FAST02 and FAST03, were scheduled with VieVS by staff of theVienna University of Technology. The sessions were performed with the antenna network of Yebes in Spain, Wettzell in Germany, Zelenchukskaya and Badary in Russia. FAST02 was a 24h-session using the S/X-DDC-mode. FAST03 was a 6h-session to test the PFB sampling. The correlation was done in Bonn, where also the geodetic analysis was made, besides some individual checks in Russia. The poster discusses andshows first results of these observations.

SchedulingScheduling

Observation modesSlightly modified GEO-SX setups were used with 16 channels and increased data rates:• FAST02 (DDC): 1GBit/s (16MHz BW, 2 bit)• FAST03 (PFB): 2GBit/s (32MHz BW, 2 bit)

The FAST sessions were scheduled with VIE_SCHED (J. SUN, 2015), the scheduling module of the ViennaVLBI Software (VieVS, Böhm et al., 2012). VIE_SCHED automatically generates geodetic VLBI scheduleswith an optimized sky-coverage at each station. On-source times are determined to meet the defined targetSNR, considering source fluxes, antenna sensitivities andthe recorded data rates. Slew times are calculatedaccording to the antenna specifications.

Scheduling parameterization• Target SNR of 15dB (S) and 20dB (X)• Minimum on-source times set to 20 sec• Bv and Zv only observed every 4th scan• Sub-netting was allowed to get a reasonable sky

coverage at all sites

FAST02 FAST03

Session start 2015-12-16 13:00 UT 2015-12-21 9:00 UT

Duration [h] 24 6

Site statistics Wn Yj Bv Zv Wn Yj Bv Zv

Obs. time [%] 42 43 12 11 42 42 11 10

Cal. time [%] 31 31 8 8 32 32 8 8

Slew time [%] 19 25 13 14 19 26 13 14

Idle time [%] 8 1 67 67 7 0 67 67

Scans num. 1658 1658 413 415 510 510 126 128

Scans / hour 70 70 18 18 73 73 19 19

Avg. scan [sec] 22 23 25 24 21 21 21 21

Table 1: Schedulesummary for FAST02 andFAST03:With the fast VGOSantennas, a remarkable largenumber of observations wasreached with an average of70 and 73 scans/hour at Wnand Yj respectively (Russianantennas only participated inevery 4th scan).

References

X-band Fourfit plot for the baseline Wn-Yj (no zoom band). The MBD is as for standard geodetic sessions.

Observation NetworkObservation Network

Correlation at BonnCorrelation at Bonn Analysis at BonnAnalysis at Bonn

ZelenchukskayaBadary

Yebes

Wettzell

Twin Telescope Wettzell (Wn), Germany- 13.2 m antenna, ring-focus design- S/X/Ka-corrugated feedhorn- 8-band up-down-converter- DBBC 2 (DDC, PFB)- Mark5B+

RAEGYEB Telescope (Yj), Spain- 13.2 m antenna, ring-focus design- S/X/Ka-corrugated horn- 6 IFs (2 pol) with down conversion- DBBC 2 (DDC, PFB)- Mark5B+

Initial Solution- Ambiguity resolution (linear clocks, Wettzell fixed)Intermediary Solution- linear splines (60min for clocks, 60min for zenith wet delays and 1d for gradients)

Final Solution- Intermediary solution with additionally estimating

baseline clock offsets for• - Yebes-Badary• - Yebes-Zelenchukskaya

Intermediary SolutionResidual plot

Zoom Band mode required:Wn & Yj -> 16 x 16 MHz channels Bv & Zv -> 3 x 512 MHz channels

MBD function degradation

LO offset required:Wn & Yj LO sum xxxx.99 MHzBv & Zv LO sum xxxx.00 MHz(avoidable if all station use the same)

ReferencesBöhm J, Böhm S, Nilsson T, Pany A, Plank L, Spicakova H, Teke K, Schuh H (2012). The New Vienna VLBI Software VieVS. In: Kenyon S, Pacino MC, Marti U (eds) Geodesy for Planet Earth, Springer Berlin Heidelberg, International Association of Geodesy Symposia, vol 136, 1007–1011Sun J, Böhm J, Nilsson T, Krásná H, Böhm S, Schuh H (2014). New VLBI2010 scheduling strategies and implications on the terrestrial reference frames. J Geod 88(5):449–461

Badary RT-13 (Bv), Russia- 13.2 m antenna, ring-focus design- Triband S/X/Ka feed- 8-band up-down-converter- BRoadband Acquisition System (BRAS) (DSC)

- Data Recording System (DRS) (VDIF)

Zelenchukskaya RT-13 (Zv), Russia- 13.2 m antenna, ring-focus design- Triband S/X/Ka feed- 8-band up-down-converter- BRoadband Acquisition System (BRAS) (DSC)

- Data Recording System (DRS) (VDIF)

&&

The activities for the construction of the 13.2 m RAEGYEB radio telescope is being cofinancied by ERDF/FEDER 2007-2013 under the project: "VGOSYEBES: Radiotelescopio de VLBI Geodesico y Astrometrico para su integracion en la red VGOS"

• - Yebes-Zelenchukskaya- outlier handling

Signifigant offsets for baselines between Qvasar stations and Wettzell/Yebes

WRMS of post-fit residuals

Results- Unexplained triangle closures between Qvasar stations and Wettzell/Yebes of about 17ns- Saw like structure in baselines with Yebes, could be explained by AC behavior (not shown here) but not eliminated

- Much more observations, e.g., Wettzell-Yebes: about 1600 obs/day w.r.t. 400 obs/day in CONT14- WRMS of post-fit residuals on the level of legacy VLBI observations- estimating, e.g., zenith wet delays with higher temporal resolutions (i.e., VGOS-like parametrization) has no physical meaning as spurious signal at Yebes dominates the residuals

Final SolutionResidual plot

Baseline WRMS [ps]

All 57

Badary-Yebes 67

Badary-Wettzell 51

Badary-Zelenchukskaya 40

Yebes-Zelenchukskaya 58

Wettzell-Yebes 60

Wettzell-Zelenchukskaya 35

(avoidable if all station use the same)

Wn & Yj data format Mark5BBv & Zv data format VDIF but 3 files: one per IF output (non-standard)

Only 5 channels at the time in X-band

X-band Fourfit plot for the baseline Bv-Wn (zoom band). In this case only 5 channels are seen because of the splitting of Bv data in 3 VDIF files, where only one was used for the test correlation.

- Correlation: ran smoothly in 32 hours- 99.9 % detection rate (high SNRs)- <1 % scan late on source- Analysis: legacy mode (S/X) comaparble to legacy VLBI- Higher temporal resolution- Still pending: 17 ns triangle closures most probably due to different station set-up

ConclusionConclusion OutlookOutlook

- Further sessions are advisable- Inclusion of other antennas would be valuable- Common station set-up needed- AC effects at Yebes need to be eliminated- Shorter scan lengths are possible (10 s)

Correlation and analysis by the IAA, RussiaCorrelation and analysis by the IAA, RussiaCorrelation was also performed with DiFX 2.4.0 on the new blade-server hybrid cluster in the IAA RAS. Because of the mixed bandwidth setup (Wn and Yj with16 MHz single channel bandwidth; Bv and Zv with 512 MHz), and also shifted sky frequencies by 10 kHz at Wn and Yj, it was necessary to use the zoom band mode of DiFX. It allows to extract exact frequency ranges from spectra for the correlation. One method is to set 10.24 MHz bandwidths of every zoom band channel to get power of 2 spectral points in correlated data used with HOPS (see Chinese RU0197). Another method is to shift the LO by 10 kHz and putting proper values in the vex file for Bv and Zv antennas (see W. Brisken). Post-processing was performed with PIMA software without Pcal adaption. The analysis was made with the “Quasar“ software suite.

Intermediary solution, residual plot (baselines by color: WnBv, YjBv, BvZv, YjWn, YjZv, WnZv)

Results from IAA, Russia