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Observations with a single dish telescope may be divided in two
- Pointed observation: The telescope beam is pointed toward a fixed
position of the source during the signal integration. In its simplest
form, the scan is composed of a spectrum whose intensity is accumulated
during the scan duration. Nothing prevents more complex scan definitions,
e.g. a scan composed of several shorter integrations, all at the same
position on the sky.
- On-The-Fly (OTF) observation: The telescope beam continuously drifts
on source during the integration to make a map of the source. The scan is
then composed of set of spectra regularly dumped (typically every 1
second) during a contiguous portion of time (typically 10 minutes). Each
dumped spectra corresponds to a different position on the sky.