SKA: Configurations and Simulations

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SKA Configurations and Simulations

• Ramesh Bhat
• Colin Lonsdale
• Roger Cappallo
• Shep Doeleman
• Divya Oberoi
• Joanne Attridge

MIT Haystack Observatory
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Simulator Functions

• A general purpose tool for LOFAR/SKA studies
• Create Synthetic Data Sets
• Performance simulations, at high level design
  specs
• Realistic effects Ionosphere, Variable beams,
  Skies
• Configuration Studies
• Explore Design Parameter Space
• Automation to allow efficient searches
• Identify trends in performance
• Testing Calibration and Postprocessing
• Direct access to structures solved for
• Controlled environment for isolation of effects
• Test New Postprocessing Algorithms
• Science Applications (e.g. EOR)

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Simulator Status

• Includes
• FITS Image import
• Variable station beams
• Thermal Noise (Rx)
• Arbitrary array configuration.
• Arbitrary station config.
• Gaussian sources
• Arbitrary time/freq obs.
• True parallelization in time.
• Functional parallelization otherwise
• Exportable to FITS
• Script driven to support automated parameter
  searches

• 4-D Ionosphere with line integration.
• Site mask incorporation
• Sky noise due to Galactic Background.
• Will Include
• Polarization
• Realistic skies
• Source Spectral Index
• Out-of-beam source contributions (CasA in
  sidelobes, etc)
• Extension to 3-D FFTs for wide field imaging.
• RFI (limited)

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Functional Flow Diagram
config generator
LOsim
obs_spec
array
skies
sites
proc_spec
Script driven Simulator Module
Calibration structures for comparison
(u,v) FITS
MIRIAD
PSF Stats Imaging Fidelity
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Image Import and Simulation
After
Before
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Effect of Variable Station Beams
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Simulator Beowulf

• 20 nodes
• 2.4 GHz P4, 900 each
• 1 Gbyte of RAM
• 60 Gbyte of disk
• Gigabit ethernet switch
• 24-port
• 2000
• UPS and misc
• Excellent price/performance
• 50-80 Gflops
• 1.5 Tbytes of disk
• lt25,000

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Configuration Studies - in progress
Proposed USSKA Configuration

• Parameter space is vast
• Configurations (log spirals, random,)
• Number of stations (variable sensitivity )
• No of elements/station, Staion layout
• Bandwidth and integration time
• Sky properties and observing geometry
• Frequency, polarization, spectrum,
• Weighting schemes, tapering
• Ranges of corrupting influences.
• Strategy parameterize configurations and explore
  limited ranges, identify trends
• Input from ALMA, ATA, SMA studies.

Inner 100 km array
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Figures of Merit

• PSF statistics RMS, size, min, max, deviation.
  Computed for declination, integration, bw.
• Cable Length (Prims Algorithm).
• Sensitivity Loss due to weighting, fixed taper.
• PSF statistics for Inner compact array/core.
• Image fidelity for a few benchmark images.
• Robustness impact of random station loss.
• Calibratability requires calibration software.

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Searching in Parameter Space
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Configuration Optimization
Figures of Merit PSF RMS vs Radius PSF Beam
Size Cable Length
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Configuration Optimization
Figures of Merit weighted And Combined into
Optmization function
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Configuration Editor
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Progress so far and Future Work

• Good progress with the simulator package,
• downstream pipeline, automation, FOMs.
• Many configs tested so far, calculation of FOMs.
  
• Continue extensive configuration studies
• Explore N, Nant/station, station layout, etc.
• Range of observing conditions, time/bw effects.
• Configuration evaluation along FOM axes
• Continue Code Development
• New modules based on priority