Statistical Calibration of the New Generation Radio Telescopes
01 / 2010 - onbekend
Radio-astronomy is undergoing a major revolution in at least three areas: (i) large increase in sensitivity due to a 100-fold increase in collecting area (SKA), (ii) the wish/ability to observe down to very low frequencies (10-300 MHz; LOFAR,LWA,MWA) where all-sky imaging and ionospheric phase-corruptions become a major challenge and (iii) the construction of wide field focal-plane-arrays (ASKAP,WSRT) allowing panoramic imaging capabilities. Several of these facilities will come on-line in the next few years. What these telescopes have in common is an enormous increase in sensitivity that require a much higher dynamic-range ($>10^6:1$). They also deliver extremely large volumes of data. In order for these telescopes to realize their full potential it is essential to 'calibrate' them extremely well. The current calibration algorithms are deterministic and 'perturbative' in nature, where they solve a set of 'measurement-equations' for the desired parameters in a stepwise fashion. The increased field-of-view offered by these arrays leads to a large increase in both the number of free-parameters and of bright sources that need to be separately calibrated, makes such an approach almost impossible. Here we propose to develop a new generation of calibration algorithms that adopt a novel approach whereby all instrumental, ionospheric and sky-signal parameters are random variables that vary with time. We will utilize statistical inversion techniques to solve the ``measurement-equations'' for the telescope's entire field-of-view simultaneously. Such algorithms are essential in order to allow full exploitation of these new arrays. As an application, the method is discussed in the context of the LOFAR Epoch-of-Reionization project.