Using baseline-dependent window functions for data compression and field-of-interest shaping in radio interferometry

TL;DR

This paper proposes baseline-dependent window functions for radio interferometry data compression, reducing smearing effects and improving field-of-interest imaging at the cost of some sensitivity, demonstrated on simulated VLA and EVN data.

Contribution

It introduces a novel approach using baseline-dependent window functions for low-loss data compression in radio interferometry, enhancing image quality and field-of-interest shaping.

Findings

Improved amplitude response within the field of interest.

Better attenuation of off-field sources.

Trade-off between sensitivity and smearing can be optimized.

Abstract

In radio interferometry, observed visibilities are intrinsically sampled at some interval in time and frequency. Modern interferometers are capable of producing data at very high time and frequency resolution; practical limits on storage and computation costs require that some form of data compression be imposed. The traditional form of compression is a simple averaging of the visibilities over coarser time and frequency bins. This has an undesired side effect: the resulting averaged visibilities "decorrelate", and do so differently depending on the baseline length and averaging interval. This translates into a non-trivial signature in the image domain known as "smearing", which manifests itself as an attenuation in amplitude towards off-centre sources. With the increasing fields of view and/or longer baselines employed in modern and future instruments, the trade-off between data rate and smearing becomes increasingly unfavourable. In this work we investigate alternative approaches to low-loss data compression. We show that averaging of the visibility data can be treated as a form of convolution by a boxcar-like window function, and that by employing alternative baseline-dependent window functions a more optimal interferometer smearing response may be induced. In particular, we show improved amplitude response over a chosen field of interest, and better attenuation of sources outside the field of interest. The main cost of this technique is a reduction in nominal sensitivity; we investigate the smearing vs. sensitivity trade-off, and show that in certain regimes a favourable compromise can be achieved. We show the application of this technique to simulated data from the Karl G. Jansky Very Large Array (VLA) and the European Very-long-baseline interferometry Network (EVN).