LOFAR calibration Ger de Bruyn & Ronald Nijboer (Calibration Project Scientist & Program Manager) Outline: 1. Calibration framework 2. LOFAR configuration overview and rescope effect 3. FOV, # sources and sensitivities 4. Review of main calibration issues 5. CS-1 and WSRT-LFFE: lessons learned 6. Calibration proces in action 7. Issues/questions for Survey KSP 8. Calibration planning priorities for 2008 Leiden, 11-Dec-2007
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LOFAR calibration Ger de Bruyn & Ronald Nijboer ( Calibration Project Scientist & Program Manager) Outline: 1.Calibration framework 2.LOFAR configuration.
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LOFAR calibration
Ger de Bruyn & Ronald Nijboer(Calibration Project Scientist & Program Manager)
Outline:
1. Calibration framework
2. LOFAR configuration overview and rescope effect
3. FOV, # sources and sensitivities
4. Review of main calibration issues
5. CS-1 and WSRT-LFFE: lessons learned
6. Calibration proces in action
7. Issues/questions for Survey KSP
8. Calibration planning priorities for 2008
Leiden, 11-Dec-2007
Basic LOFAR calibration framework (see e.g. Noordam, 2006, LOFAR-ASTRON-ADD No.15)
‘Novel’ ingredients (compared to standard selfcal)
- Direction/position dependent corrections
- Phase (ionosphere) => ‘non-isoplanaticity’
- Gain (beam) => elevation/azimuth dependent sensitivity
=> image-plane vs uv-plane correction solving/treatment
- All sky calibration, wideband synthesis and imaging
- Global Sky Model needed (spectral index, structural parameters, polarization)
- w-term always very important (w-projection, speed issue)
- Full polarization Measurement Equation (Hamaker etal)
(Jones matrix description: B, G, E, I, .. : 2x2 matrices , complex and scalar)
Measurement Equation (incomplete) (taken from Sarod Yatawatta,’s Droopy Dipole Memo)
Configuration overview and effect of rescope
1) Core-NL balance:
range of stations: from 18+18 to 24+24
2) Station configurations (xx gives # dipoles or tiles)
Core: LBA48 and HBA24+HBA24
NL: LBA48 and HBA48
Europe : LBA96 and HBA96
3) UV-coverages: superstation, core, NL-LOFAR
4) Rescope effect: sensitivity ~ 3x less
survey speed ~ 3x less
(NB: SurveySpeedFOM = Aeff2 X FOV )
LOFAR core 24LBA and 2x24HBA
HBA 25x2 stations 4h +45o
LOFAR sensitivity table (Dec07)
N=40
N=60
N=20
N=40
LOFAR beam/FOV table
Review of calibration problems/challenges and ‘solutions’
Question: How to get to the thermal noise?
What are relevant ‘noise’ contributions? Thermal (see Table)
Sidelobe noise from large # sources: ~ 2 x Sminx psf x N
Classic Confusion noise (~ 0.2 mJy at 30 MHz, L ~ 75 km)