Surveys KSP Project Description
Developing, commissioning and carrying out the large-sky LOFAR surveys require several preparatory tasks to be carried out in close collaboration with the LOFAR Project. The LOFAR Project will deliver all the necessary hard- and software needed to observe with the telescope and to create well-calibrated maps on the basis of 5 hours of data. The DCLA project is charged with developing the needed tools for (i) scheduling of the surveys, (ii) controlling the data quality and determining acceptable observing conditions, (iii) administering the data, (iii) combining images, (iv) source finding and characterization and (vi) producing final maps and publishable source catalogues. In addition they are deeply involved in the development of methods to calibrate ionspheric disturbances due to the impact of the ionosphere on the radio emission.
In doing this, the DCLA will make use of the Astro-Wise (AWE) information system that is capable of handling large streams of imaging data. AWE couples pipelines, archives and processors in a single working environment. To be able to use the pipeline, a set of routines need to be written that allows the AWE system to read in the maps and its associated meta-data. Using these tools, an administration system needs to be built that is capable of (i) performing basic quality checks on the incoming images, (ii) maintaining a data base of the images and associated meta-data, (iii) combining incoming images into large mosaics, (iv) carrying out source detection and measurement, (v) carrying out thorough quality checks to ensure that the astrometric and photometric fidelity of the images and source lists are within specifications, (vi) determining spectral indices of sources in the catalogue and (vii) making the images and source lists available on a www-server. An important task is to write the software needed to carry out the source detection and measurements. A major challenge is to take into account the varying PSF over the image due to the expected imperfection of the ionospheric calibration.
A second important task for the survey KSP is the testing, commissioning and optimisation of the imaging and calibration techniques prior to carrying out the planned large surveys. There are a number of critical parameters that must be determined from astronomical commissioning activities as input to these software tools and in determining acceptable ionospheric and RFI conditions for reaching the goals. These include (i) interference excision, (ii) the complexity of ionospheric model needed for calibration, (iii) the stability and number of degrees of freedom of the beamshapes, and (iv) the number of calibration and deconvolution computational cycles required. This requires the following activities for the complete range of LOFAR observing frequencies: (i) obtaining observations during a variety of ionospheric and RFI conditions, (ii) processing the obtained data through the reduction pipeline, (iii) performing extensive quality checks, and (iv) optimising the critical input parameters of the reduction pipeline.