Optimising SKA1-Mid scale-dependent sensitivity

In this report we study the scale dependent sensitivity of the SKA1-Mid baseline design. We also propose changes to the baseline design that enhance the sensitivity at smaller angular scales (e.g. 0.4-1 arcsec at 650MHz) without compromising the performance at larger scales. The changes we propose are guided by the SKA1-Mid level-zero science requirements [2], which suggest that very long baselines (> 150km) are not necessary to achieve the SKA1-Mid science objectives. The layouts we propose could be transformational for other potential science cases which are possible with such an instrument, such as cosmology with weak lensing, at no significant cost to any of the key science cases. In particular, a layout which has a maximum baseline of 120km (SKA1X9-12A72B120) has more than twice the survey speed of the “second generation” baseline layout at angular resolutions of around 0.4-1 arcsec (over 650-1100MHz). Furthermore, such a layout spans significantly less space which could potentially reduce trenching and data transport costs.