7. Observing Modes
7.1 ON-OFF Techniques
In order to reduce as much as possible the atmospheric contribution during an observation, it is possible to apply some techniques based on the comparison of at least one pair of exposures, one on-source and one on an adjacent area ("OFF source" reference position), sufficiently free from emission.
At high frequencies short-scale and strong atmospheric fluctuations affect the observation, hence the need for quick antenna shifts between the two positions (which have to be reasonably close to each other).
The Medicina antenna offers the following ON-OFF technique:
The antenna shifts between two different positions.
The time needed to cover a distance of a few beams is nearly 5
seconds at all frequencies.
continuum observations (in modes: ON-OFF, OTF cross-scans,
OTF maps, raster maps) an Exposure
Time Calculator is now available.