Jan-Willem W. Steeb, David B. Davidson and Stefan J. Wijnholds,
"Spatial filtering of near-field radio frequency interference at a
LOFAR LBA station," RFI worshop 2016, Socorro, New Mexico (USA),
17-20 October 2016.
abstract:
In preparation for the SKA, many new RFI (radio frequency
interference) mitigation algorithms have been developed. However,
these algorithms usually assume that the RFI source is in the
far-field and that the array is calibrated. In this paper, the
recovery of astronomical signals from uncalibrated RFI-corrupted LOFAR
visibility data using spatial filtering methods are presented. For
this demonstration, a near-field continuous-wave RFI source was
generated by a hexacopter that was flown around one of the LOFAR LBA
(low-band antenna) arrays. Four spatial filtering methods were applied
to the RFI contaminated data: orthogonal projection, orthogonal
projection with subspace bias correction, oblique projection and
subspace subtraction. Overall, orthogonal projection with subspace
bias correction performed the best, however it requires that the RFI
source moves relative to the array and it is computationally
expensive. Oblique projection performs similar to orthogonal
projection with subspace bias correction when point sources are to be
recovered and is furthermore considerably less computationally
expensive. Subspace subtraction is a suitable alternative if a large
field of view is to be recovered at a relatively low computational
cost.
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