Courtesy: JPMacquart

Connecting early VLBI to SKA capabilitiesArnold van Ardenne

Astron SKA Program Officeardenne@astron.nl

SKA Paradigm shifts:• Sensitivity• Ultra Deep polarimetric imaging• Connectivity, flexibility • Field of view, time variable observing• Multi- vs. Single sky pixel processing Courtesy: JPMacquart

Richards contributions to key areasto imaging in Radio Astronomy

NGC 4438: Image GMRT HI (150 Million Solar masses) on optical map (southern hemisphere)

Hydrogen 21 cm

Messier 81 in the Big Dipper

Improved Sensitivity ~105x in 50 years

Angular resolution (θ = λ/ D) • Dwingeloo 25m @ 21cm 0.5deg• Effelsberg/GBT 100m @ 21 cm 8’• Westerbork-SRT 2500m @ 21 cm 15”• Very Large Array 30km @ 2cm 0.15”• SKA/VLBI 1000km @ 3cm 4milli”• Space VLBI 400.000km @ 6cm 20μ” • mm VLBI 10.000km @ 350GHz 15μ”

Improvement AngRes

•Improved calibration and processing e.g. M.E.

•Now: High resolution high Dynamic range (“clean”) images

~107x in 50 years; in 70 years?

Cygnus A with the VLA

Optical

~ELT/VLTI-IR

NGC 6946: deepest WSRT HI map ever (16x12h)

With SKA:~107x in 70 years

VLBI and more…Areas of known and expected progress

Early VLBI high resolution• Limited # baselines• Limited Bandwidth ~1MHz• 1- bit Taperecorders• Post-observing processing• Time sync. through Long wave

receivers (LORAN, DCF77), TV• Single telescope station

– Herogeneous telecopes

• Limited polarimetry, limited DR

Toward SKA• Many baselines; excellent uv-cov. • High bandwidth ~>GHz• Real-time through fiber networks• Real-time processing & observing• Time diss. through GNSS, other? • High stability phase coherency?• Complex observing

– Homogeneous within SKA, possible heterogeneous for highest resolution?

• Highest DR polarimetric imaging

Now: Look into some specific areas of less obvious change made possible through Richard

Time dissemination through Televison synchronisation

First VLBI Observation Dwingeloo telescope 1976

Phase coherency through Rubidium clock (on loan from Nat. Bureau of Stds/VSL

Data collection throughMark II taperecording(on loan from NRAO)

Signal conditioning and Data formatting through IF & formatter(on loan from NRAO)

1610MHz, 3 Baselines, OSO, Dwingeloo, Effelsberg, 3C236, A&A 1979

Important equation for VLBI:

Fotos RTS from Huib Jan

Correlated flux:

NRAO 2 station correlator 1977

Fudge factor to make it all fit

Aperture Synthesis = imaging in high resolution mode

D=3km

Westerbork Array (Neth.) East – West configuration of 14 antennas; Full synthesis in 12 hours

and (many) more!

Tied arraying: Emulating a single large telescope

D

Equivalent Diameter max 93 mi.e. 25x√14

In-phase addition of all the signals from all telescopes

Adding a pulsar observing capability in passing

Recv.Recv.

Equal.Equal.

IVCIVC

ADCADC

Recv.Recv.

Equal.Equal.

IVCIVC

ADCADC

Receivers in 14 telescopeswest east

Cables to central building

Central building

TADU

TADU

LOLO LOLOVLBIVLBI

CorrelatorCorrelator

Ref. Ref.

Imaging Mode (normal)

Phased Array Mode(Etot=ΣEn)

Synchronous Aperture synthesis observations of pulsarsR.G. Strom and H. W. van Someren Greve, Astroph& Space Sc., vol 171, 351-355, 1990PuMaPuMa

For the WSRT (status 1987)

Outside the cabin: MKII/MKIIIBefore (end 70-ties): MKII only

Inside the cabin: Digital Adding box

Tied (phased)arraying: What happened to simplicity?

Correlated flux:

b=b(std)

b=b(std).Dd(n, ρ, TAn , Q,..)

Dde=(excess)Digital degradation factor

Tied arraying: lessons from adding signals toward the SKA

Westerbork Array (Neth.) East – West configuration of 14 antennas as tied array:

Equiv. Diameter max 93 mi.e. 25x√14

• Concept of Effective Area ÷ Effective signal temperature

• Maximum for equal antennas/receivers AND analog addition (analog BF!)

• Example: 10% loss with 14 telescopes, 4 bit A/D

Need: More bits, more receivers

B. J. Kokkeler, P. Fridman, A. van Ardenne, “ Degradation due to quantization noise in radio astronomy phased arrays”, Journal for Experimental Astronomy , Vol 11, 33 – 56, Feb. 2001

Systems toward SKA

•Number of elements “large” i.e. tens or hundreds?

•So far: Quantization 8-12 bit

•For SKA-AA’s:– ~> 8 bit?

•Relevant to SKA-Dish? –Dish tied arrays?

Flexibility, beams and computations

Courtesy: Jan David Mol, Jason Hessels, John Romein

Connecting Clockstability with VLBI

AvA NFRA-Note 463, 1984

Increasing the resolution further

1.Ames, H.; Bolton, S.; Burke, B. F.; Burks, S.; Christensen, C.; Dhawan, V.; Freland, B.; Grippi, D.; Hamilton, C.; Hansen, D.; and 40 coauthors, “Quasat: technical aspects of the proposed mission”, ESA Spec. Publ., ESA SP-213, p. 27 – 99, 1984

And many more e.g. P.J. Diamond, J. M. Moran, K. I. Kellerman, D. J. Launcey etc.

~35000km

Phase/time transfer through satellite

A. van Ardenne, J. D. O’Sullivan, A. de Dianous, “A High-Precision Phase-Comparison Experiment Using a Geostationary Satellite”, IEEE Trans. Instrum. and Meaurement, Vol IM-32, Nr.2, pp 370-376, 1983

S.T. Ables; Phase stability with the Aussat satellite, ATNF, 1989

J. Bardin, S. Weinreb, and D. BagriLocal Oscillator Distribution using a Geostationary Satellite, J. Exp. Astronomy, 2004(?)

Doing phase transfer with OTS2 at ESTEC site, 1981

Two way-single station, 11.5 /14.2GHz

Quasat did not work out but…

Lessons learned:

•Applied to new system in Westerbork Array ic. MultiFreq. Frontends (MFFE); turret concepts for SKA?

•Full understanding on how to design coherent phased arrays

Last but not least; Organizing the organizations

• For VLBI– EVN– JIVE

• Toward Europe and elsewhere

• For SKA– Toward SKA Org.

• Striking right balances

Shaping up through numerous SKA-ISSC’s, SSEC’s WS’s etc.,

Thanks and good luck!