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