Huib Jan van Langevelde Joint Institute for VLBI in Europe, Dwingeloo NL radio-astronomy a telescope...

Huib Jan van LangeveldeHuib Jan van LangeveldeJoint Institute for VLBI in Europe, Dwingeloo NLJoint Institute for VLBI in Europe, Dwingeloo NL

radio-astronomyradio-astronomya telescope larger than Europea telescope larger than Europe

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2/19Geant, Bled, Slovenia, March 4 2008

Outline

• Radio-astronomy• About resolution and sensitivity• Introducing Very Long Baseline Interferometry

• e-VLBI, how the Network becomes the telescope• Hardware, infrastructure, protocols• An operational e-VLBI network• Science objectives

• Special requirements• Guaranteed bandwidth, dedicated light-paths• Intercontinental VLBI

• Beyond operational network• Current R&D programme• Directions in radio-astronomy• Ambitions for future e-VLBI programmes

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Radio-astronomy

• Radio waves with λ of 0.7mm to 90cm

• Compared to optical light 400 – 700 nm

• Can be detected and amplified with antenna

• radio emission from hot gas between the stars

• Super bright emission from vicinity of black holes

•Active Galaxy at 1cm radio emission

•Connected Radio-Interferometry like Westerbork with long baselines can observe interesting detail in radio sources

•Need even longer baseline to see astronomy in motion!

•Radio emission from astrophysical plasmas can be detected against sky noise with telescopes larger than few meters

•To reach interesting resolution need kilometer baselines

•Interferometer measures Fourier components of the sky brightness

Dλθ ≈

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VLBI digital processing

•To reach the faint end of the universe…

• Need many big telescopes• And as much frequency

space as you can get• i.e. bandwidth!bandwidth!

radio sources in the Hubble deep field require several days of integration (Garrett et al., 2000)

•Current standard is 1Gb/s • Recording 256 MHz in 2 pols• bits are not sacred, losses

tolerable• Recording on parallel hard

disks

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Now turn to e-VLBI!

• Upgrade EVN to e-EVN• Funding through EXPReS

project in 2006• Retrofit correlator to work real-

time• Help solve last mile problem at

telescopes• Work closely with NRENs on

robust connectivity

• And become operational at a competitive sensitivity

• Push to 1024 Mb/s limit• Bring in the big telescopes• And start the revolution in

radio-astronomy culture

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Remarkable progress

•6 telescopes regularly on line, interesting for science•Correlator operations optimal for direct results and feedback

•Connectivity reached impressive reliability•Started with TCP, but obviously not the optimal protocol for e-VLBI•Now dedicated light-pathslight-paths to most telescopes•UDP protocols implemented for optimal streaming

Size of balloon set by number of telescopes participating, height by station sustained bit-rate

Number of telescopes @ data rate

61 2

4

35

-128

0

128

256

384

512

640

768

896

1024

1152

1280

Aug/03 Mar/04 Oct/04 Apr/05 Nov/05 May/06 Dec/06 Jun/07 Jan/08 Aug/08 Feb/09

Data rate (Mbps)

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Recent progress

•Managed to get almost full sensitivity at 1024 Mbps

• Selectively dropping data

•Got connectivity to big 100m telescope at Effelsberg (D)

• In collaboration with LOFAR

•Major issue for astronomical competitiveness

•First science runs in April

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Made lots of progress

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Why e-VLBI is exciting for science?

• Rapid response for rapid variability• Fast response to requests• Immediate analysis of data, adapt observing parameters• Coordination with current and future observatories

• Immediate feedback• More robust data

• Fewer consumables, logistics• Constantly available VLBI network

• Monitoring: for example astrometry• Spacecraft tracking

• Growth path for more bandwidth • More sensitive astronomy

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Link to China

MiyunUrumqi

Seshan

Kunmin

TEIN2

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Long-haul connectivity

• Important milestone: can be done!

• Across cultures and firewalls...

•Long round trip time was a real challenge

• Cannot be done with TCP/IP• UDP over light-paths

•Done a few more tests• Arecibo on Puerto Rico• Done correlation of Australian

antennas•Yielding unique astronomy results

• And China of course• Small test to Chile

•Must do more• To South-America• To South Africa• Most US antennas are not connected!

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Doing R&D for future e-VLBI

•10 Gbps connectivity coming up

•Development of data acquisition system required

•Interface to UK eMERLIN system•Connectivity to Onsala (SE) telescope

•And Metsahovi (FI)

•Working on distributed software correlator

•Prototype operational for quality control

•Grid enabled•Looking for P-ops regime•Not sure this is cost effective

• Power and cooling bill

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Roadmap of future telescopes

LOFARLOFARSKA and SKA pathfindersSKA and SKA pathfinders

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What we achieved & learned

• e-VLBI is an operational, robust facility in Europe

• Enabling unique science from the start• Reaching competitive level with all telescopes and 1 Gb/s

for any science application

• Requires light-paths for optimal performance• Had to overcome some network quirks for special

applications• But when it runs it really flies on Geant!

• Can do even intercontinental VLBI• Were able to overcome problems with delays

• e-VLBI is the grow path for more sensitivity• And global VLBI!

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Wish list...

• Light paths, probably dynamically allocated• To accommodate distributed correlation

• And around the globe in some uniform manner • Must continue close collaboration with

NRENs/GEANT• Will use 10Gb/s to make fellow astronomers

forget conventional VLBI...• but not quite ready for that

• Considering some improvements in VLBI architecture:

• Buffering data at telescopes and correlator for robustness• Maybe involve more supercomputing/GRID in the future?• Must address a number of things at astronomy side

• Decide on correlator architecture for next generation• Keep a focus on Global e-VLBI, incl NRAO antennas in the US• Develop common ground with E-LOFAR• Continue to explore technological synergy with SKA

on behalf of EXPReS partners:

and: all our friends at NREN’s

Huib Jan van Langevelde Joint Institute for VLBI in Europe, Dwingeloo NL radio-astronomy a telescope...

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