vlbi inteferometry

8/3/2019 VLBI INTEFEROMETRY

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Internet Interferometry at Onsala:

cm eVLBI and LOFARJohn ConwayVxj, June 17th, 2008

Present work at Onsala Space Observatory, SwedishnaNonal facility for radio astronomy

Long Nme involvement in interferometry, VLBI, ALMAetc.

Involved with interferometry over the internet since2004.


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Interferometry

Radio interferometry, correlate electric fields between twoseparate radio telescopes (baseline). Measures one Fourier

component of 2D brightness distribuNon.

Using large arrays and rotaNon of Earth measure many spaNalfrequencies, Fourier invert and process to make images.

Can synthesize an aperture of diameter D, hence resoluNonlambda/D. In Very Long Baseline Interferometry (VLBI) D can

approach Earth diameter.

Paradox although radio is longest wavelength has highestresoluNon in astronomy!

For observaNons of conNnuum sources sensiNvityproporNonal to 1/sqrt(Bandwidth observed)


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First TransatlanNc Radio

Interferometry, Onsala, January 1968

VLBI- Record data on computer tape, physically ship tapes to

a correlator, results months later First transatlantic fringes

above found to antennas in US, Haystack (MIT) and

Greenbank (NRAO, WV)


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Old style VLBI, circa 2005

Not real time collapse of wavefunction(!) Takes

months, limits science, also observe blind


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First TransatlanNc Real Time Fringes

Demo at iGRID 2005 conference, September 2005

succesful fringes Onsala-Haystack


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Onsala Internet Interferometry

Overview EXPReS EU funded programme3 Projects

ProducNon eVLBI at 1Gbps data rate tocorrelator in etherlands now operaNonal

Test of 4Gbps into correlator in UK LOFAR, new low frequency radio telescope at2.5Gbps to etherlands


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EXPReS

EU FP7 InformaNon Science Technology Infrastructure project March 2006 October 2009.Total budget 12.5MEuro. EU contribuNons

3.9MEuro

Total of 19 partners, radio telescope and academicnetworks (EU but also US,China, Chile, Australia)

Main goals 1Gbps producNon service + 4Gbps demo(OnsalaUK) + distributed soware correlaNon.Onsala money for networking + person. Local PI

myself, also lead Science forum.


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eEVN: European VLBI Network

1-10 Gbps

Data processing

centre:

16 Gbps (2008)1 Tbps(2011?)

China

USA

South

Africa

Russia

asymmetricstar topology


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eVLBI Results

OH masers

Paragi, September

2007. Rapid position

finding of radiosupernova. First

eVLBI astronomy

telegram


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eMERLI

eMERLI, max 250km interferometer OpNcal fibre links 30 Gb/s from each

telescope

2 x 2 GHz using 3 bit samples 2 x 0.5 GHz using 8 bit samples 1.31.7, 48, 2224 GHz ew/modified receivers, lenses, IF, data

links, correlator, s/w

EXPReS deliverable 4Gbps from Onsala into eMERLIN

correlator at Jodrell Bank and do demo correlaton with

eMERLIN stations


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iBOB + ADC

Internet Break out Board Berkeley Wireless group

FPGA chip UDP packetiser written to sample and transmitat up to 16Gbps


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JANET

NetNorthWest

Jodrell Bank

JIVE +

LOFAR.

FUNET

Metshovi

SUNET

OnsalaNORDUnet routed IP

(simplified view)

GANT2

Rest ofSUNET

NORDUnet TSS Opto

TSS L2Cloud

STO CSC

CPH

Rest of

FUNET

SurfNET

SUNET

project router

VLANs

HAM

Network Infrastructure- lots of

cooperation with SUNET,

NORDUNET


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Very Recent Progress

Last week demonstrated 4Gbps from iBoBat Onsala through to Jodrell Bank UK

Also last week demonstrated 8Gbps fromOnsala to Metsahovi in Finland (8 timeshigher data rate than disk recording!)

But hav not done correlation yet of thesehigh bit rates requires eMERLIN correlatorin UK, ready Autumn 2008. Eventually

Onsala to become a a part time eMERLIN

station?


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LOFAR the radio telescope

Radio antennas (staNons) distributed over theetherlands + Europe

Frequencies: 30 240 MHz Pathfinder for the Square Kilometre Array

(SKA) at lowfrequencies

Dutch baselines: up to 100 km European Expansion to 1000 km


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The radio antennas

Low Band Antenna- (10) 30MHz - 80 MHz

- 96 dipoles per station- Within NL only 48 can

be used at a time

High Band Antenna- 120 MHz - 240 MHz

- 1 tile = 4 x 4 antennas- 48 tiles per station

(Within NL)


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A new generaNon Radio telescope

Replace big dishes by many cheap dipoles in staNons o moving parts: electronic beam steering

observe mulNple direcNons at the same Nme

Bandwidth of 32 MHz; channel width ~ 1kHz Supercomputer (IBM BlueGene )correlates the data

& data is being processed on cluster

Current funding allows 36 staNons of dipoles + extrasensors (geo+agro) within the etherlands.

European level 7 staNons fundedAmbiNon to build more staNons


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Key Science Projects

Four key science projects have driven thedevelopment:

Epoch of ReionisaNon (de Bruyn, Groningen) ExtragalacNc Surveys (Rgering, Leiden) Transients and Pulsars (Wijers, Amsterdam) Cosmic ray detecNon (Hrandel/Falcke, ijmegen)

Two key science projects recently added: Solar science and space weather (Mann, Potsdam) Cosmic MagneNsm (Beck, Bonn)


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LOFAR core

Inter tile distance: 0.6m

96 LBAs

24 HBA tiles 24 HBA tiles


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LOFAR L

Inter-tile distance = 0.6m

96 LBA

48 HBA tiles


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ELOFAR

96 HBA tiles 96 LBAs

Inter-tile distance: 0.6m


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1st LOFAR international station

Effelsberg ISDE01


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LOFAR at Onsala

Research council planning grant for 2006/2007 (600kKr =70kEuro). MeeNngs, RFI (radio frequency interference) test of oursite by ASTROposiNve result

ovember 2007 Swedish research council applicaNon for fundinga full LOFAR staNon was successful (6.8Mkr = 600kEuro). ++

Timeline, site preparaNon, Autumn 2008, staNon installledin Spring 2009

Swedish involvement in Key science projects now possible

Swedish astronomers will get back some guranteed observing Nme


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OSO LOFAR Topographic map

2008 06 04

Roadto25mInfiltration

Dirt

road

Stone walls


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OSO LOFAR Site prepara5on

Picture showing area after

site preparation

Rock blasted in

30deg el from

the 70m d limit

340 + 80 m3 filling needed

(reuse stone from the blasting)

About 1 hectare forest

have to be cut down


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OSO LOFAR Final configura5on


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OSO LOFAR Orienta5on

2008 06 04Leif Helldner

Container

Closest distance, Tile - dipole

Roadto25m

Infiltration

Dirt

road

Distance (cc) HBA - LBA

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