Calibration and imaging challenges at low radio frequencies: An overview of the state of the art

Many scientific deliverables of the next generation low frequency radio telescopes require high dynamic range imaging. Next generation telescopes under construction indeed promise at least a ten-fold increase in the sensitivity compared with existing telescopes. The projected achievable RMS noise in the images from these telescopes is in the range of 1--10$\mu$Jy/beam corresponding to typical imaging dynamic ranges of $10^{6-7}$. High imaging dynamic range require removal of systematic errors to high accuracy and for long integration intervals. In general, many source of errors are directionally dependent and unless corrected for, will be a limiting factor for the imaging dynamic range of these next generation telescopes. This requires development of new algorithms and software for calibration and imaging which can correct for such direction and time dependent errors. In this paper, I discuss the resulting algorithmic and computing challenges and the recent progress made towards addressing these challenges.