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S.P.A.M.

S.P.A.M. Source Peeling & Atmospheric Modeling (Intema et al. in preparation). SPAM package overview. Ionospheric phases are obtained from peeling sources in primary beam Phases are mapped on thin layer ionosphere at fixed height (200-400 km)

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S.P.A.M.

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  1. S.P.A.M. Source Peeling & Atmospheric Modeling (Intema et al. in preparation)

  2. SPAM package overview • Ionospheric phases are obtained from peeling sources in primary beam • Phases are mapped on thin layer ionosphere at fixed height (200-400 km) • 2D model is fitted using dominant terms in Karhunen-Loève basis, assuming Kolmogorov turbulence • Primary beam is imaged while applying model corrections to small patches of sky

  3. Example: SPAM ionospheric model fit

  4. Succesful application to VLSS data • VLSS: VLA@74 MHz, 1.5 MHz BW, 80’’ res.,12 deg. FOV • B-configuration (up to 10 km baselines),but low decl. field have AnB configuration(up to 22 km baselines) • Uses field-based calibration (Cotton et al. 2004) • Average noise level is ~100 mJy/beam

  5. VLSS 1300-208 field • AnB configuration • Number of bright (> 10 Jy) sources • Noise level ~120 mJy / beam • Evidence of excessive smearing due to ionosphere

  6. VLSS 1300-208 image

  7. SPAM 1300-208 image

  8. 1300-208: 7 sigma source detections VLSS image SPAM image

  9. 1300-208: SPAM versus VLSS • 70 versus 120 mJy/beam • 300 versus 150 source detections (7 sigma) • Less smearingof sources (higher peak fluxes)

  10. General: SPAM versus VLSS • Does not / does assume compact array configuration • Ionospheric model fit domain is attached to Earth / sky • Uses adaptive KL basis / non-adaptive Zernike basis • Nice / horrible extrapolation properties • Possible / impossible to extend to 3D

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