# Investigations on MultiView VLBI for SKA

## TL;DR

This paper evaluates the potential of MultiView VLBI with SKA to significantly improve astrometric accuracy by reducing systematic errors, leveraging increased sensitivity and multiple simultaneous observations.

## Contribution

It provides a quantitative assessment of MultiView VLBI's applicability and accuracy improvements for SKA, suggesting increased VLBI beams for optimal performance.

## Key findings

- Systematic errors of ~10 μas with current VLBI for distant calibrators.
- Error reduction to a few μas for in-beam calibrators.
- Recommendation to increase VLBI beams from four to ten for SKA.

## Abstract

The SKA will deliver orders of magnitude increases in sensitivity, but most astrometric VLBI observations are limited by systematic errors. In these cases improved sensitivity offers no benefit. The best current solution for improving the accuracy of the VLBI calibration is \MV\ VLBI, where multiple simultaneous observations around the target are used to deduce the corrections required for the line of sight to the target. We have estimated and quantified the applicability of \MV\ from real-world ionospheric studies, making projections into achievable astrometric accuracies. These predict systematic measurement errors, with calibrators separated by several degrees, of $\sim$10\uas\ with current VLBI facilities. For closer calibrators, that are in-beam for single dish VLBI facilities, we predict systematic measurement errors of a few \uas. This is the ideal combination, where the sensitivity of the SKA will provide the precision and \MV\ will provide the accuracy. Based on these results we suggest that the SKA design should increase the number of VLBI beams it can form from four to as many as ten.