LOFARLOFARStatus as of June 2003Status as of June 2003

Colin Lonsdale

What is LOFAR?What is LOFAR?

• Major new array for 10-240 MHz range

• 400 km across, fixed dipole receptors

• Fully digital, all-sky coverage, extreme agility

• Planned initial operation in 2006

• Three-way collaboration

– ASTRON, in Dwingeloo, Netherlands

– Naval Research Lab (Remote Sensing Div.), Washington

DC

– MIT/Haystack

LOFAR:

Overall layout 400 km diameterRemote operations centers

One LOFAR station, ~150 meters

Array layout

~130 antennas generate 250 Gbit/sec

Filtering and beamforming reduces this to ~2 Gbit/sec

Outer 3/4 of stations create ~150 Gbits/sec aggregate

Central core, 2km, ~3300 antennasAggregate data rate ~ 6 Tbit/sec

When and Where?When and Where?

• What is the timeline?– Target for initial operations – 2006– Target for full operation – 2008– Instrument lifetime – decades, with upgrades/refinements

• Site selection– Three candidate sites

• Netherlands• Southwest USA• Western Australia

– Completion of technical evaluation in July– Announcement of preferred site expected by September– Decision needed to permit focused design

Current StatusCurrent Status

• Preliminary Design Review, June 3-5– All systems except antennas and receiver– Delta-PDR scheduled for early September

• Subsystem Critical Design Reviews– Second half of 2004– System-level CDR in late 2004

Redshifted HI from the Epoch of Reionization

High-z starbursts

Galaxy clusters and the IGM

Cosmic ray distribution, and airshower radio bursts

Steep spectrum and fossil radio galaxies

Supernova remnants and ISM energy budget

Interstellar recombination lines

Nearby pulsars, ghost nebulae

Extrasolar gas giant planetary radio emission

Stellar flares

Interstellar medium propagation effects

Transients, GRB and LIGO event counterparts, buffering

Solar radio studies

CME detection, mapping by IPS, scattering

Extremely high resolution ionospheric tomography

Magnetospheric radar

Tozzi et al. (2000)

Courtesy: B. Gaensler

Courtesy: B. Jackson

Lane et al. (2001)

Scientific VersatilityScientific Versatility

Low frequency antennaLow frequency antenna

• Inverted-V shaped dipole– Electrically short design

• Possible because sky noise dominates

• Broadband

– Simple, cheap, robust– Comes in 2 sizes, LBL and LBH

PrototypingPrototyping

• THETA (10 single polarized LBH elements)– Sky noise dominated in 40-

80 MHz band

HF Antenna arrayHF Antenna array

• Nominal 4x4 crossed dipole array• Electronic analog beamforming/steering

– PC board switched delay lines (used before at 74 MHz)

• Low cost is main challenge

Single 4x4 unit

Multiple units may be butted together for economy and performance

HF Antenna PrototypingHF Antenna Prototyping

LNA

~4 meters

Possible station configurationPossible station configuration

LF antenna layout

HF antenna layout

Trunk fiber

RFI-shieldedstation electronics hut

Coaxial cables

~150 m

~50 m

Station beamformer architectureStation beamformer architecture

9 beams108 antennas12 outer boards3 inner boards1 center board

F1

B2

B1

B3

F2

WAN I/F

Physical beamformer layoutPhysical beamformer layout

A

B

C

A

C

A

B

C

B

C

B

A

AAAABBBBCCCC

AAAABBBBCCCC

AAAABBBBCCCC

1 2 3 4 6 7 8 9 11 125 10 13 14 15 16

1 2 3 4 6 7 8 9 11 125 10 13 14 15 16

Outer RingBoards

Inner RingBoards

WAN I/FBoard

To

AD

C u

nits

Station Digital Processing - statusStation Digital Processing - status

Transient bufferingTransient buffering

• Large cyclical RAM buffer per antenna– Buffer contains full FOV information

– Upon trigger, can point LOFAR post-facto

– Tradeoff between duration, sensitivity

• Implement subsystem, add more RAM later– 100 secs at 4 MHz = $600k in RAM chips, 2005 prices

All Sky MonitorAll Sky Monitor

• Run 100% of time in the background• Make ~1000x1000 pixel map of sky every 0.5 sec

– Full cross-correlation of 3200 antennas– 5.4 million baselines– Full field of view

• Integrate on wide variety of timescales• Search for transient events, generate triggers

• React to triggers– Re-point one or more LOFAR beams– Freeze and download the data buffer

Huge discovery potential

WAN ImplementationWAN Implementation

• Viable and affordable technologies identified• Requirement vary across array

– Implementation matched to specific needs– Inexpensive, very high bandwidth for short-haul

• Strong emphasis on mass-market components

C en t ral P ro ces s in g P lat fo rm

R o u t er C lu s t er

4 0 k m SM F

6 s egm en t s w it h 4 0 k m d is t an ce p er s egm en t

3 0 0 k m

1 0 G B A SE-ER1 0 G B A SE-EWSp ec 1 5 5 0 n m

R em o t e St at io n

1 6 SM F fib ersD C F

Eth

erne

tPADPAD PAD

SO A s

Central ProcessorCentral Processor• ~1000 nodes in a 3D switching fabric• Bandwidth 2 Gbit/sec point-to-point

Know your EnemyKnow your Enemy

• Virgo A• VLA 74 MHz

Effect of Variable Station BeamsEffect of Variable Station Beams

LOFAR CalibrationLOFAR Calibration

• Maximize ratio of knowns/unknowns

– Make lots of independent measurements

– Know as much as possible about sky a priori

– Know the instrument (e.g. response to environment)

– Solve for smooth functions wherever possible

– Gather a priori knowledge of ionosphere (e.g. GPS)

• Bootstrapping approach to selfcal

– Develop solutions for strong sources & subtract

– Interpolate and improve coherence for weaker sources

– Develop solutions for weaker sources & subtract

“Peeling” – prototyping in progress

Redshifted HI from the Epoch of Reionization

High-z starbursts

Galaxy clusters and the IGM

Cosmic ray distribution, and airshower radio bursts

Steep spectrum and fossil radio galaxies

Supernova remnants and ISM energy budget

Interstellar recombination lines

Nearby pulsars, ghost nebulae

Extrasolar gas giant planetary radio emission

Stellar flares

Interstellar medium propagation effects

Transients, GRB and LIGO event counterparts, buffering

Solar radio studies

CME detection, mapping by IPS, scattering

Extremely high resolution ionospheric tomography

Magnetospheric radar

Tozzi et al. (2000)

Courtesy: B. Gaensler

Courtesy: B. Jackson

Lane et al. (2001)

Scientific VersatilityScientific Versatility

Sensitivity

Resolution

Field of View

Agility

Many detectable phenomena

Broad scientific appeal

SummarySummary

LOFAR is:

• Technologically challenging (= exciting …)

• Scientifically spectacular

• Making swift technical progress

• Gathering momentum