CAOBS - Compact Array Observing Program

CAOBS is the main observing program for the Australia Telescope Compact Array. At this stage all the documentation for the use of this program is provided by the AT Users' Guide.

Some additional, auxilliary information is provided here.

DE_BIRDIE An experimental algorithm for the removal of the 128MHz sampler clock harmonics from observing bandpasses.
The command to control the cx and ls noise diode is SET DIODE ON/OFF/SWITCHING
The command to control the paddle for the mm horn is SET PADDLE IN/OUT . Note that the control line for this is shared with the noise control diode, it will always be set to switching by this command.

OTF Mosaicing

A new, experimental, OTF (on the fly) Mosaic mode is now available for caobs. In this mode the antennas will scan across the mosaic points instead of moving to and stopping at each pointing. This means that we do not have to flag data at the start of each cycle (when the antennas are moving in mosaic mode). For large, low frequency mosaics the OTF mode should be more efficient.

During an OTF mosaic, the phase center follows the mosaic points as specified, and the pointing center moves continuously across the pointings. In effect the primary beam of the antennas becomes elongated (to 1.5 beams) in the scanning direction.

To satisfy proper sampling of the sky, the antennas should not move by more than half a beam per integration cycle, so the spacing of pointings in the mosaic file should be the same as before. The way this is implemented in caobs assumes you are scanning in rows or columns, the direction of scanning is inferred from the next point. At the last point of a row or column the previous direction is maintained to complete the scan. One extra point, marked with the name TURN, needs to be specified at the start of the next row/column, to allow for the antennas to change direction and scan at the correct speed again. As an example, here is a 3x3 grid around 1934-638:

  0.0000  0.0      2  $@1934-on C
 -0.1812 -0.16     1  $TURN-10 
 -0.1812 -0.08     1  $1934-11 
 -0.1812  0.00     1  $1934-12 
 -0.1812  0.08     1  $1934-13 
  0.0000  0.16     1  $TURN-24
  0.0000  0.08     1  $1934-23 
  0.0000  0.00     1  $1934-22 
  0.0000 -0.08     1  $1934-21 
  0.1812 -0.16     1  $TURN-30 
  0.1812 -0.08     1  $1934-31 
  0.1812  0.00     1  $1934-32 
  0.1812  0.08     1  $1934-33

Note that you can specify a non-scanning position in an OTFMOS file by starting the field name with a "@", like the 2 cycle calibration on 1934-on above. Also note the fields marked with TURN - these are the extra points required at the start of each row/column to give the antennas time to get to the correct position and scanning speed. They should be discarded when processing the data. To try out the OTF mosaic mode, specify a scantype of OTFMOS in atcasched and put a mosaic file like one the above in /atca/mosaic/ on xbones.

This mode could also be used for mm observations by using bin mode and moving the antennas by e.g., 16 beams in a single integration with 32 time bins. The miriad program atlod will need some work to properly record the phase center and pointing center in this case.