Hi Josh,
The earth-rotation-synthesis version of the synthesized beam for
configuration (c) [Figure 5c, right panel] seems to have a grating
pattern in the sidelobes that's not present for configurations (a) and
(b). I don't feel like I have a great sense for what the practical
effect of that might be, but it seems potentially worrisome for
imaging. Do you have a sense of where that comes from?
Peter
On Sat, 2016-01-16 at 13:23 -0800, Josh Dillon wrote:
> Dear HERAtics,
> Aaron and I have been working on investigating how to arrange the
> “inriggers" and outriggers for HERA. In particular, we’ve been
> interested in two questions: 1) how do modifications to the
> configuration affect imaging? and 2) how do they affect the ability
> to redundantly calibrate the array (including outriggers) using
> Omnical? That work will become a paper relatively soon (hopefully,
> before the proposal goes in).
> The key result is an idea for an array that includes a change to the
> array core. Basically, I want to split it up into three segments,
> each relatively displaced by less than the minimum baseline length.
> This is something we should talk about as a collaboration, so I’d
> like to give everyone something to think about before the next
> telecon.
> I’ve attached the current draft of that paper (which is just an
> abstract, outline, figures, and captions right now) that helps lay
> out the argument. Basically, the proposed configuration (which is
> configuration (c) in the paper) is more robustly calibratable with
> Omnical, produces lower calibration errors, and modestly suppresses
> sidelobes.
> The key figures to look at are 1, 2, 3, 4, 10, and 11. The first four
> show the proposed configurations and the instantaneous baseline
> redundancy patters they produce. Both configurations (b) and (c) are
> designed to tile the uv plane nicely, putting new baselines where
> information is sparsest. Figures 10 and 11 show the expected gain
> errors on the antennas after logcal, both with and without the
> outriggers. The other figures have to do with imaging, where the
> effect is more subtle, and are harder to understand without the
> supporting text that I still need to write.
> Perhaps the most surprising result is that my original attempt to
> produce perfectly tiled sub-grid baselines (see Figure 2b) actually
> leads to larger calibration errors throughout the entire core by
> approximately 10%. That’s because Omnical is trying to solve for a
> lot more visibilities with very little information about them. That’s
> the main reason I think the split-core is preferable to the kind of
> “inriggers" proposed in configurations (a) and (b). The split core
> also allows for complete simultaneous uv-coverage at triple density
> out to ~400 meters.
> In case anyone is curious or wants to try doing a calculation with
> them, I’ve attached text files with positions of the split-core +
> outriggers (HERA-361). I’ve also attached a slightly more symmetric
> version with 11 core antennas removed (HERA-350), that currently
> Dave, Aaron, and I favor.
> Of course, I welcome any feedback. Enjoy your long weekend (of
> proposal writing)!
> -Josh
