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1. Mapping (https://science.nrao.edu/facilities/vla/docs/manuals/obsguide/modes/mosaicking#section-2)
   1. Angular spacing along rows of a discrete mosaic – what scalar for what mapping?
      1. 1.2 (Nyquist)
      2. sqrt(2)
      3. sqrt(3)
   2. If less the integration time is less than 15 seconds, we use OTF?
   3. the phasecenter cannot change faster than 0.6, 0.5 seconds?
   4. the scan rate cannot be greater than 3 ? 10 arcminutes/s? (https://science.nrao.edu/facilities/vla/docs/manuals/opt-manual/observation-preparation-tool/scan-modes-obs-modes/on-the-fly-mosaicking)
   5. How large of an extent in RA can be tolerated for OTF mapping?
   6. Should the highest part of the band be used to determine mapping parameters or should the center frequency? (depends on science)
2. Calibrator and Wrap
   1. Another inconvenient wrapping situation appears when observations near zenith (elevations larger than about 80°) switch between sources on different azimuth wraps. This happens when a target and calibrator are close to, but on opposite sides of 34.1° (34°04′42.497′′) declination (latitude of the VLA). The OPT will show slew times much longer than expected for the angular source separation, and indicate an azimuth wrap (CW or CCW) on only one of the sources in the reports of the scan list. So even if a calibrator may be a bit further away or less strong, it may be the better option when it is on the same side of zenith. Experiment with different LST start times to investigate the effect for a particular SB if no suitable calibrator can be found on the same side of zenith. (https://science.nrao.edu/facilities/vla/docs/manuals/obsguide/dynsched/antenna-wraps )

VLBA

1. Reliable calibrations can be obtained for sources observed with an elevation above 20 degrees for most VLBA antennas. JIVE (https://planobs.jive.eu/) uses 10 degs as a hard cut-off for elevation for any given station. It is possible to observe less than that cut-off however. Generally, at lower frequencies, there is "spill-over", which is emission from the ground. At high frequencies, there is more atmosphere along the line of sight, which increases the difficulty in calibrating. The RFI is also more severe at lower elevations.

Reflections

1. For GBT observing, there are less predicable "stressors" on the time estimate. For example, AutoOOF solutions during the daytime are good for 30 minutes to 4 hours, depending on the sun, cloud cover, etc. Would it be useful to give a range, Delta(total time requested), or a best case /worst case time ranges for Overhead?

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