SKA: Configurations and Simulations

Ramesh BhatColin LonsdaleRoger CappalloShep DoelemanDivya Oberoi

Joanne Attridge

MIT Haystack Observatory

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)

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)

Functional Flow Diagram

array skies obs_spec sitesproc_spec

configgenerator LOsim

Script driven Simulator Module

(u,v) FITS

MIRIADPSF StatsImagingFidelity

Calibrationstructures forcomparison

Image Import and SimulationBefore After

Effect of Variable Station Beams

• 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

– <$25,000

Simulator Beowulf

Configuration Studies - in progress

• 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.

Proposed USSKA Configuration

Inner ~100 km array

Figures of Merit:

• PSF statistics: RMS, size, min, max, deviation. Computed for declination, integration, bw.

• Cable Length (Prim’s 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.

Searching in Parameter Space

Configuration Optimization

Figures of Merit:PSF RMS vs RadiusPSF Beam SizeCable Length

Configuration Optimization

Figures of Merit weighted And Combined into Optmization function

Configuration Editor

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