4 research outputs found
A morphological algorithm for improving radio-frequency interference detection
A technique is described that is used to improve the detection of
radio-frequency interference in astronomical radio observatories. It is applied
on a two-dimensional interference mask after regular detection in the
time-frequency domain with existing techniques. The scale-invariant rank (SIR)
operator is defined, which is a one-dimensional mathematical morphology
technique that can be used to find adjacent intervals in the time or frequency
domain that are likely to be affected by RFI. The technique might also be
applicable in other areas in which morphological scale-invariant behaviour is
desired, such as source detection. A new algorithm is described, that is shown
to perform quite well, has linear time complexity and is fast enough to be
applied in modern high resolution observatories. It is used in the default
pipeline of the LOFAR observatory.Comment: Accepted for publication in A&
A BSP/CGM Algorithm for Finding All Maximal Contiguous Subsequences of a Sequence of Numbers ⋆
Abstract. Given a sequence A of real numbers, we wish to find a list of all non-overlapping contiguous subsequences of A that are maximal. A maximal subsequence M of A has the property that no proper subsequence of M has a greater sum of values. Furthermore, M may not be contained properly within any subsequence of A with this property. This problem can be solved sequentially in linear time. We present a BSP/CGM algorithm that uses p processors and takes O(|A|/p) time and O(|A|/p) space per processor. The algorithm uses a constant number of communication rounds of size at most O(|A|/p). Thus the algorithm achieves linear speed-up and is highly scalable.