Statistics
Scientific paper
Aug 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006iauss...6e..22u&link_type=abstract
Astronomical Data Management, 26th meeting of the IAU, Special Session 6, 22 August, 2006 in Prague, Czech Republic, SPS6, #22
Statistics
Scientific paper
In this paper, we present salient features of the hierarchical RFI mitigation system developed and implemented for offline processing of the visibilities recorded at MRT. Its aim is to achieve effective, reliable and non-toxic automatic RFI mitigation with minimal human intervention. RFI poses a serious problem at MRT due to its low frequency of operation, wide primary beam (EWxNS~2°x56°) and large amount of data collected for a low frequency survey. Even though several signal processing methods are used to handle RFI, in practice there is no universal foolproof technique. The developed system uses a conjunction of a variety of techniques involving linear and non-linear methods in the visibility as well as in the image domain. These include Thresholding, Fourier filtering, Hampel filtering, Model fitting, Visual inspection, multi-parameter decision based algorithm which uses cumulative interference statistics, and the fact that the sky signal is correlated in each day's images but interference is most likely not. More than 99.7% of the interference is detected automatically, the remaining is detected by semi-automatic methods. The images obtained after applying the RFI mitigation system are free from any perceivable interference and demonstrate its effectiveness. The principles and techniques used in the RFI mitigation system are of general nature. We believe that such an approach based on a conjunction of techniques exploiting their natural strengths and judiciously applying them at various stages of data processing is an important step in the future direction of research to accomplish the ultimate goal of achieving completely automatic data flagging. Use of an RFI database is valuable to investigate the nature of interference at an observatory site and develop appropriate techniques based on its statistics for its mitigation. The 20,000 hours of astronomical observations for the MRT survey have been used for such an analysis. The interesting aspects of interference statistics are highlighted in the second part of the paper.
Pandey Vishambar N.
Shankar Udaya N.
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