Array Configuration
description
Transcript of Array Configuration
![Page 1: Array Configuration](https://reader036.fdocuments.us/reader036/viewer/2022062315/56816504550346895dd772ba/html5/thumbnails/1.jpg)
Array Configuration
Divya OberoiMIT Haystack Observatory
![Page 2: Array Configuration](https://reader036.fdocuments.us/reader036/viewer/2022062315/56816504550346895dd772ba/html5/thumbnails/2.jpg)
In the 512T world…
• Capture order 5% of total visibilities with native correlator resolution
• Assume/imagine complete flexibility about which visibilities can be captured
• Question - How to choose which visibilities to capture?– 128T 1/16th of the visibilities– Get a sense for what sort of uv coverage can an
optimally chosen set of 128 tiles provide
![Page 3: Array Configuration](https://reader036.fdocuments.us/reader036/viewer/2022062315/56816504550346895dd772ba/html5/thumbnails/3.jpg)
Characteristics of the Radio Sun
The “quiet” Sun is more dynamic than previously thought. Oberoi et al., 2011, ApJ, 728, L27
![Page 4: Array Configuration](https://reader036.fdocuments.us/reader036/viewer/2022062315/56816504550346895dd772ba/html5/thumbnails/4.jpg)
8 minutes
200
1000
Freq
uenc
y (M
Hz)
GSRBS + RSTN (San Vito)White et al., unpublished
The “active” Sun, we know, can be fantastically dynamic.
![Page 5: Array Configuration](https://reader036.fdocuments.us/reader036/viewer/2022062315/56816504550346895dd772ba/html5/thumbnails/5.jpg)
Smerd, 1970
Complex morphology and emission at a range of angular scales
Mercier et al, 2006, A&A, 447, 1189
![Page 6: Array Configuration](https://reader036.fdocuments.us/reader036/viewer/2022062315/56816504550346895dd772ba/html5/thumbnails/6.jpg)
The Solar Radio Imaging Problem
The Sun is a challenging source to image• Time variations – sub millisec to solar cycles• Spectral variations – variety of spectral scales
down to few 10s of kHz• Complicated and dynamic morphology• Emission at variety of spatial scales – from
~10” to order a degree.
![Page 7: Array Configuration](https://reader036.fdocuments.us/reader036/viewer/2022062315/56816504550346895dd772ba/html5/thumbnails/7.jpg)
Optimization Criterion
• Optimize for – High fidelity, monochromatic, snapshot imaging– FoV size ~1°
– Emphasis on maximizing the uv plane sampling
![Page 8: Array Configuration](https://reader036.fdocuments.us/reader036/viewer/2022062315/56816504550346895dd772ba/html5/thumbnails/8.jpg)
Implementation
• Compute zenith uv coverage (300 MHz)• Divide uv plane in uv cells corresponding to 1° FoV• Compute occupancy of each uv cell• Compute a weight for each tile defined as
– WTile (# of visibilities in a uv cell) Sum over all uv cells to which a tile contributes – a measure of how many uv cells does a tile contribute to,
weighted by how many tiles (not baselines) contribute to that uv cell
• Remove the tile with the smallest weight and iterate
1
![Page 9: Array Configuration](https://reader036.fdocuments.us/reader036/viewer/2022062315/56816504550346895dd772ba/html5/thumbnails/9.jpg)
Results 1. - Configuration
![Page 10: Array Configuration](https://reader036.fdocuments.us/reader036/viewer/2022062315/56816504550346895dd772ba/html5/thumbnails/10.jpg)
Results 2. – uv coverage
![Page 11: Array Configuration](https://reader036.fdocuments.us/reader036/viewer/2022062315/56816504550346895dd772ba/html5/thumbnails/11.jpg)
160 MHz
Nyquist grid sampling
![Page 12: Array Configuration](https://reader036.fdocuments.us/reader036/viewer/2022062315/56816504550346895dd772ba/html5/thumbnails/12.jpg)
Nyquist grid sampling128 T
512 T
![Page 13: Array Configuration](https://reader036.fdocuments.us/reader036/viewer/2022062315/56816504550346895dd772ba/html5/thumbnails/13.jpg)
The Message• The optimization criterion for EoR and Solar imaging have a
natural tension simply due to the characteristics of the emission they are after
• 512T regime– Very large N + small foot print significant scope for simultaneous
optimization for both EoR and (Solar) imaging science• 128T regime– With only 6.25% of the baselines, not enough room to
simultaneously accommodate disparate needs– A ‘compromise’ configuration will not serve any of the science
objectives well
![Page 14: Array Configuration](https://reader036.fdocuments.us/reader036/viewer/2022062315/56816504550346895dd772ba/html5/thumbnails/14.jpg)
The VLA approach
• 27 antennas• 4 configurations, switch configuration every ~4 months• Remarkably successful strategy - broad science appeal
and a very capable instrument• 78.6 MUSD in 1972
Leverage the investment in the most expensive parts of the instrument (dishes + backend + infrastructure) by investing in the flexibility to move the dishes to broaden the scientific capability and returns very significantly.
![Page 15: Array Configuration](https://reader036.fdocuments.us/reader036/viewer/2022062315/56816504550346895dd772ba/html5/thumbnails/15.jpg)
A VLA like strategy for MWA• Expensive parts – Infrastructure, Receivers
perhaps Correlator• Install more than 128 tiles (+ BFs), 128 of which
can be connected up at any given time• Relieve some of the tension in array configuration
optimization by providing more flexibility• Change array configuration say twice a year - EoR
observing season, when the EoR fields are up at night, change to a “imaging” optimized config during the rest of the year
![Page 16: Array Configuration](https://reader036.fdocuments.us/reader036/viewer/2022062315/56816504550346895dd772ba/html5/thumbnails/16.jpg)
A VLA like strategy for MWA…
• Use the Rx node locations based on the present 512T config, but the tile locations need not be limited to the current choices
• The Rxs themselves will need to be moved to derive the most benefit from this approach
• An interesting option for the MWA to examine in detail
![Page 17: Array Configuration](https://reader036.fdocuments.us/reader036/viewer/2022062315/56816504550346895dd772ba/html5/thumbnails/17.jpg)
Conclusion• Solar imaging performance is crucially tied to the choice of
array configuration • Preserving high fidelity monochromatic, snapshot imaging
capability is the single most important requirement for solar imaging science
• Need the long baselines (2.5 km baseline ~3’ @ 150 MHz)
• An ability to connect up different array configurations can significantly broaden the science returns from the MWA, an interesting option worth exploring in some detail