- Explore the performance of imaging quality of an ALMA Cycle 0 configuration that can be obtained by combining several short snapshots at different hour angles.
- Run a case where the image is dynamic range limited, and one where it is thermal noise limited.

- Start with Band 7 (345 GHz), Cycle 0 ES-extended configuration, Dec = -35 deg
- Create a field with 3 bright sources (1, 0.5, 0.25 Jy), and five fainter ones: 10, 5, 2.5, 1 mJy, and a second 0.5 mJy adjacent to the brightest one
- Create a second field without the 3 bright sources
- Simulate both with simdata for an 8 hour track, and flag portions of the data corresponding to different numbers of snapshots
- Include atmospheric noise but not phase noise (since with bright sources, self-cal should remove most of the phase noise)
- Clean interactively like an observer would do, with appropriate small boxes
- Compute the dynamic range as the ratio between max peak flux density of brightest source divided by image rms (computed over a source-free region that represents a significant fraction of the area within the half-power beam diameter)

- 480 minutes
- Full 8-hour track (480min) cleaned down to 1mJy
- amp vs. time (ant#0 baselines only), image
- rms of 0.164 mJy/beam: Max = 0.83, dynamic range = 5061, rms is 5 times worse than without the 3 bright sources
- with 10% pwv phase noise: rms = 1.44 mJy/beam, but Max dropped to 0.097
- with 5 um rms phase noise: rms = 0.268 mJy/beam, Max is 0.83Jy

- Full 8-hour track (480min) cleaned down to 1mJy
- 180 minutes (rms would be 0.27 scaling the 8-hour track)
- One x 180 minutes cleaned down to 1.3mJy
- rms of 0.31mJy/beam, Max = 0.823, dynamic range = 2670

- Three x 60 minutes spread over 6.5 hours
- rms of 0.30mJy/beam, Max = 0.830, dynamic range = 2800

- One x 180 minutes cleaned down to 1.3mJy
- 64 minutes (rms would be 0.45mJy scaling the 8-hour track)
- Eight x 8-minute snapshots (64min) spread over 8 hours
- amp vs. time, image
- image rms of 0.41 mJy/beam, Max = 0.83, dynamic range = 2024, rms is 4.4 times worse than without the 3 bright sources
- 5um phase noise gives 0.77 mJy/beam

- Three x 21-minute snapshots spread over 7 hours
- image rms of 0.62 mJy/beam, Max = 0.83, dynamic range = 1351

- One 64min observation at transit
- amp vs. time
- image rms = 1.0mJy/beam, Max = 0.82Jy, dynamic range = 820, rms is 1.39x worse than splitting into 8 chunks

- Eight x 8-minute snapshots (64min) spread over 8 hours
- 32 minutes (rms would be 0.64 scaling the 8-hour track)
- Four x 8-minute snapshots (32min) spread over 6 hours
- amp vs. time
- rms = 0.72 mJy/beam, Max = 0.83 Jy, dynamic range = 1153, rms is 5.5 times worse than without the 3 bright sources
- with 5um rms phase, new rms = 1.18mJy/beam

- Three x 10.67-minute snapshots spread over 4 hours
- amp vs. time
- rms = 0.73 mJy/beam, Max = 0.83 Jy, dynamic range = 1137

- Two x 16-minute snapshots spread over 4 hours (with one at transit)
- amp vs. time
- rms = 0.89mJy/beam, Max = 0.83, dynamic range = 932

- One 32 minute observation near transit
- amp vs. time
- rms = 1.59 mJy/beam, Max = 0.82 Jy, dynamic range = 516
- rms is 2.21x worse than splitting into 4 chunks, 2.18x worse than splitting into 3 chunks, 1.94x worse than splitting into 2 chunks

- Four x 8-minute snapshots (32min) spread over 6 hours
- 15 minutes (rms would be 0.93 scaling the 8-hour track)
- One 15 minute observation near transit
- rms = 2.0 mJy/Beam, Max = 0.82 Jy, dynamic range = 410

- One 15 minute observation near transit
- 1 minute: rms = 4.6 (would be 3.6 scaling the 8-hour track)
- 20 seconds: rms = 6.6 (would be 6.2 scaling the 8-hour track)

Time (hours) | Sensitivity calculator noise (mJy/beam) |
Achieved noise |

8 | 0.038 | 0.032 |

1.067 | 0.104 | 0.094 |

0.533 | 0.147 | 0.141 |

- 480 minutes
- Full 8-hour track cleaned to 0.1mJy (image)
- image rms = 0.032mJy
- Max = 9.3mJy, dynamic range = 291

- Full 8-hour track cleaned to 0.1mJy (image)
- 64 minutes
- Eight x 8-minute snapshots spread over 8 hours
- rms = 0.094 mJy
- Max = 8.98 mJy, dynamic range = 96

- Eight x 8-minute snapshots spread over 8 hours
- 32 minutes
- Four x 8-minute snapshots spread over 8 hours
- rms = 0.127 mJy
- Max = 9.02mJy, dynamic range = 69

- Three 10.67-minute snapshots over 4 hours
- rms = 0.135 mJy
- max = 9.29 mJy, dynamic range = 69

- Two 16-minute snapshots over 4 hours (with one at transit)
- rms = 0.142
- Max = 9.24 mJy, dynamic range = 65

- One 32-minute observation near transit
- rms = 0.141 mJy, which is 1.11x worse than splitting into 4 chunks, 1.044x worse than 3 chunks
- max = 9.23 mJy, dynamic range = 65

- Four x 8-minute snapshots spread over 8 hours

This topic: Main > TWikiUsers > ToddHunter > HunterALMASimdata

Topic revision: 2017-05-04, ToddHunter

Topic revision: 2017-05-04, ToddHunter

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