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Astronomical Data Simulations Cormac Reynolds DS2-T2 Team 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds Overview • Re-cap of the DS2-T2 goals • Potted highlights from each of the WPs • Simulations Framework and Collaboration 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds Aperture Array and FPA Modelling, Plus a Configuration Study Abstracted model of telescope from Tile and Network Simulations Simulated Skies from a number of science groups (line, continuum, polarization) Produce simulated u,v data/images for scientific analysis Telescope based on aspects of SKA Reference Design – SKADS Benchmark Specification Simulated skies (DS2-T1) 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds AA and FPA Simulations • Need to describe in simulations software • Requires full “measurement equation” for phased arrrays – – – – – – Pointing errors Bandpass shape & stability [f(,)] Sensitivity [f(,)] Beam shape and stability [f(,)] Polarization purity [f(,)] ionosphere 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds AA Beam - Sundaram • EMBRACE beam – HPBW ~ 16 arcmin • depends on elevation • Pointing error – linear rise and fall 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds PPP – Ultimate FoV Limit to Polarization Purity - Carozzi • There is a limit to polarization purity as a function of look-direction elevation angle • This limit is due to aberrations arising from u,v projection of low-elevation sources 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds FPAs & Beam forming Boomsma + = By changing the (complex) weights for each element, one can optimise the beam pattern. For example: reducing sidelobes 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds Configuration Studies -Lal Attempt to maximise the Spatial Dynamic Range Spatial dynamic range (SDR) – the ratio between largest and smallest adequately imaged scales – it measures, effectively, brightness sensitivity of an array on all scales. SDR reflects a number of aspects of array design, including the type of primary receiving element (antenna), signal processing, and distribution of antennas/stations. Array configuration: SDR can be expressed as a function of a „gap“, u/u, between adjacent baselines (u1,u2): u/u = (u2 – u1)/u2 (u2 > u1) Uniform sensitivity is provided by u/u = const 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds Figures of Merit Shortest spacings, a few 10s of metres ~degree Longest spacings (5000m) ~arcseconds 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds Preliminaries An arbitrary choice of source model Observing 1.4 GHz Observing direction, RA 00:00:00 Dec +90:00:00 A RUN of 12 hrs 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds Methodology Generate test array (X,Y) for logarithmic (equiangular) spiral array configuration Project this array on Earth’s surface and determine (Lat, Lon, Z) Choose an appropriate input source model RUN glish scripts in aips++ to obtain visibilities Import these visibilities into AIPS and perform the mapping using IMAGR task. Determine the “figures of merit” 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds Results The behaviour of figures of merit and hence the SDR does not seem to have a simple dependence on u/u. The uv-gap parameter can be used to relate the (u,v)coverage to the characteristics of the map. These empirical solutions can be implemented into any proposed configuration. We plan to use the SDR FoM to quantify imaging performance of: KAT / MEERKAT, ASKAP, SKA – Phase I Limitations of CLEAN deconvolution algorithm Need new algorithms and parallelisation. 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds Ionosphere - van Bemmel • How to design SKA so that ionospheric corruptions are calibratable • Determine the number and sensitivity of stations needed so that the free parameters related to the description of the beams and ionosphere can be determined with sufficient signal to noise that high dynamic range maps can be made 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds Simulated source + calibration distortions using 74 MHz data 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds Solving • Method – Peeling produces phase corrections per array element for several viewing directions – Fit an Ionosphere phase screen model to these phase corrections – The model allows for interpolation of the phase corrections to other viewing directions – We adopted the polyhedron method for imaging, calculating one phase correction per array element per time interval for each facet within the FOV. • First conclusions • Encouraging first results, with some improvement over the existing field-based calibration by Cotton et al. (2004) • Performance of new method is very dependent on the choice of model functions 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds 3 x 2.5 degree VLA-B 74 MHz field with fieldbased calibration applied Same field with new calibration method applied 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds Next • Finalize work on solver – Investigate more base functions – Apply to longer baselines: GMRT (150 MHz) and VLA • Use DS2-T1 model skies 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds DS2-T2 <=> DS2-T1 • Take sky model, corrupt, return to T1 for analysis – Sky simulations: galore! – Turning them into a Global Sky Model (GSM) • Arbitrary parameterizations (e.g. trees) – Making corrupted data-sets – Recovering the sky again (calibration) • Tricky... 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds Various simulation efforts • LOFAR – dipole and station beams (S. Yatawatta) – ionosphere (M. Mevius, J. Anderson) – Local Sky Model (LSM) (everybody...) • WSRT (J. Noordam) • SKADS – – – – model skies (everybody...) ionosphere (I. van Bemmel) AA beams, pointing errors (S. Sundaram) FPA beams (T. Willis, R. Boomsma) • DIGESTIF (R. Boomsma, T. Oosterloo) 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds How to make things just fit together? • TDL is a good basis for exchanging trees • The ME provides a mathematical framework – someone makes a sky model – someone else makes a tree for computing Jones matrices – at least you know how to plug them together (mathematically) • But we still have a software problem – different styles, different conventions 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds Simulations Framework Smirnov Configurable catalogue parser Ideal visibilities Array config and observation setup Note that order of Jones terms is significant... Z-Jones ionosphere Alternate Z-Jones E-Jones Beam Alternate E-Jones G-Jones Gain Alternate G-Jones ... Alternate Jones Differential/Corrupted Vis. (for calibration...) 2nd SKADS Workshop 10-11 October 2007 ... Cormac Reynolds Simulations - Siamese 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds 2nd SKADS Workshop 10-11 October 2007 Cormac Reynolds