Position Switching

Single dish observations are explicitly differential: the signal from the On position (target+sky) is compared with the signal from the Off position (sky only). In position switching, the telescope points back and forth between the target and a nearby blank sky position.

UIP commands

  1. Position switching with reference positions 300 arcsec (5 arcmin) away in azimuth.
    uip> oo_scan N /step 300 /altaz
    • The telescope will move symmetrically
      +OFF ON ON -OFF
    • N is the number of repetitions of this pattern.
    • Because the sky brightness does not change, moving in azimuth results in better subtraction.
  2. Position switching with reference position chosen to avoid emission regions, etc.
    uip> oo_scan N /designated_off
    • The telescope will move asymmetrically
      OFF ON
    • N is the number of repetitions of this pattern.
    • The reference position must be specified in the source catalog as target:off_position.

There are other possibilities. For details, consult the online help,
uip> help oo_scan


  • If the Secondary mirror is wobbling, it will be stopped before an oo scan, then restarted.
cso/instruments/heterodyne/onoff.txt · Last modified: 2014-04-09 21:33 by sradford
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