Calibration Challenges for Future Radio Telescopes

TL;DR

This paper reviews the calibration challenges faced by future large-scale radio telescopes, emphasizing the complexity of estimating numerous direction-dependent parameters for accurate astronomical imaging.

Contribution

It provides a signal processing perspective on the daunting calibration problem posed by next-generation distributed radio sensor arrays.

Findings

Calibration complexity increases with array size and field of view.

Direction-dependent parameters significantly complicate calibration.

Accurate calibration is critical for meaningful imaging in future telescopes.

Abstract

Instruments for radio astronomical observations have come a long way. While the first telescopes were based on very large dishes and 2-antenna interferometers, current instruments consist of dozens of steerable dishes, whereas future instruments will be even larger distributed sensor arrays with a hierarchy of phased array elements. For such arrays to provide meaningful output (images), accurate calibration is of critical importance. Calibration must solve for the unknown antenna gains and phases, as well as the unknown atmospheric and ionospheric disturbances. Future telescopes will have a large number of elements and a large field of view. In this case the parameters are strongly direction dependent, resulting in a large number of unknown parameters even if appropriately constrained physical or phenomenological descriptions are used. This makes calibration a daunting parameter estimation task, that is reviewed from a signal processing perspective in this article.