Calibration, sensitivity and RFI mitigation requirements for LOFAR

In radio astronomy, cosmic sources are observed which are many orders of magnitude weaker than the telescope system noise level. The necessary sensitivity is achieved by large telescope collecting areas, long integration times, and large bandwidths. In the coming two decades, telescopes are planned which are even one to two orders of magnitude more sensitive than the current generation. Examples are the Low Frequency Array (LOFAR), currently under construction in the Netherlands, and the Square Kilometer Array, for which the envisaged start of construction is in 2012. For this next generation of telescopes, a dynamic range in the sky maps of over 10⁶ is required. In order to reach these numbers, accurate calibration is needed. As these telescopes will observe with relatively large bandwidths, and because of the changing spectrum environment, interference mitigation techniques become increasingly important. Approaches for calibration and interference mitigation are presented, and results from the LOFAR initial phased array test station (ITS) are given.