Daily Image
01-02-2007LOFAR Interference Detection Study
| Submitter: | Mona Moren, Albert-Jan Boonstra |
| Description: | This all-sky movie gives an example of an active interferer (RFI) monitoring system capable of detecting interfering sources. Each Image was obtained from LOFAR ITS test station visibility data, using an MVDR beam former. Here the main focus is on a 9.7 kHz frequency bin centered at 15.004 MHz observing frequency. The all-sky two-dimensional grid used has a resolution of two degrees on both x-axis and y-axis; the time difference between successive images is approximately eight minutes. A variant of the Clean algorithm was used to determine the positions and strengths of the interfering sources. As the purpose of this algorithm is to give a rapid first estimation, the loop gain used is one. The cleaning threshold was set at seven dB above the median power level in the image, assuming sources above this threshold are mainly (though not always) due to RFI. The detected interferers have been added to an inventory. On the actual images, only the first two strongest sources detected are marked with an ‘X’. The image has been scaled according to the median power level, which makes it easier to visualize the variation of the strength of an interfering source over time. These algorithms can potentially be incorporated in calibration techniques of LOFAR, for instance by tracking an RFI source, and applying a null in the interferer direction. |
| Copyright: | ASTRON 2007 |
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