a.r. offringa - lofar - university of british...
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LOFAR
André Offringa – June 15, 2011
The LOFAR-EoR project
and the LOFAR collaboration
(many slides from Ger de Bruyn and Michiel Brentjes)
LOFAR(and a little bit of RFI)André Offringa – June 15, 2011
The LOFAR-EoR project
and the LOFAR collaboration
(many slides from Ger de Bruyn and Michiel Brentjes)
The LOFAR telescope
LOFAR's key properties:● 10-90 and 110-300 MHz● Beamformed stations from dipoles, tiles● Wide field of view● Very flexible observing modes● Large collecting area● Core in the Netherlands● International baselines up to 1000 km.
18 core stations(all split-stations with 2x24 tiles)
+ 4 more stations in core(CS011,013,028,031)
1 km
LOFAR's correlator
● Software correlator (Blue Gene, Groningen)● Very flexible● Superb frequency resolution: 0.76 kHz● Default integration time: 1 sec● Currently 48 MHz bandwidth, upgrade to 96
(192?) MHz.● Bandwidth and beams interchangeable, e.g.
24 x 2 MHz beams.
LOFAR key science projects
● Epoch of Reionization!● Pulsars & transients● Survey● Magnetism● Solar (system)● Ultra high energy physics / CR
The LOFAR – EoR project
● Exposure/field: 100 x 6h● 112-190 MHz● Raw resolution: 1s / 0.76 Khz● After RFI detection, average time and freq
5-10 times.● Raw data rate: 30 TB/h● Averaged data rate: 0.2 – 0.4 TB/h
LOFAR offline processing
● Standard pipeline:– Flags (AOFlagger),
– Averages (NDPPP),
– Subtracts bright sources (demixing),
– Calibrates (BBS),
– Images
LOFAR offline processing
● Offline processing on cluster of ~100 nodes
● Sub-bands are concurrently processed.● Averaging + flagging takes 25%-50% of
observation time.
AOFlagger
● Very fast & accurate
● Rough estimate of astronomical data
● SumThreshold● Iterative (2.5x)● Density dilation
LOFAR and RFI
● RFI environment behaves well● Few percentage of data requires flagging● High frequency resolution!● Antennas on the ground