Mosaic polarisation calibration in large interferometric datasets

In this project Johannes will develop techniques to extract polarisation (and other) calibration information from large interferometric databases from observations using mosaic strategies. Such mapping produces overlapping fields, so that individual sources are seen at multiple off-axis angles. By using the multiplicity of such sources it is possible to assess the accuracy of any polarisation and polar diagram calibrations that have been applied to the data and to calculate corrections to those calibrations or to derive new calibration tables ab initio. A training dataset from the ATCA is available for initial assessment and code development, and the method will then be applied to LOFAR (and possibly other) datasets. The aim is to develop a tool suitable for the data volumes that will come from the SKA, and to allow on-the-fly calibration and data quality assessment. Complications arise from the frequency-dependence of the calibrations and the varying geometry of the fields relative to the antennas being used to make the measurements, as well as the RFI environment. New science can be extracted from the existing dataset, to resolve issues with the polarised source count raised by inconsistent recent survey results, and to study the history of magnetic field growth in the intergalactic medium.