Speaker
Description
Typical radio-interferometer observations are performed assuming the source of radiation to be in the far-field of the instrument, resulting in a Fourier relationship between the observed visibilities in the aperture plane and the sky brightness distribution. When such observations are performed of events in the near-field, radiation with curved wavefronts are correlated with far-field delays resulting in loss of signal coherence in the reconstructed images of the event. In this talk, I will briefly discuss the near-field aperture synthesis techniques developed using the Murchison Widefield Array, using a single Phase 3 observation of the ISS (as it appears as a bright near-field event). Much like how the phase center of an observation can be changed post-observation, we can perform visibility phase corrections to bring the observed near-field event into the ‘focus’ of the array. Using animations of the MWA ISS observation, I show how the visibility sampling in the aperture plane (UVW grid) curves to match the curvature of the near-field wavefront, enabling coherent image reconstruction of the near-field signal. Finally, I conclude my talk by demonstrating how the distance to the near-field events can be inferred from the phases of the visibilities, i.e, inverting the curvature of the radiation to obtain a range measurement.
| Presentation length | short |
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