Sets the observing mode to be used. The observing modes describe different ways in which the data-taking occurs, and may be specified as a number in the range 1-2, or by name. The observing mode names are:
Direct_Imaging, Nod
In Direct_Imaging mode, single exposures are obtained for each run.
In Nod mode, successive exposures are obtained in an ABBA pattern at
two positions on the sky defined by telescope focal plane
apertures named N1 and N2. This is designed for use with the
grisms. The number of AB pairs obtained is set by the REPEATS
parameter which can be changed during data acquisition. If the SHOW
parameter has been set to CURRENT with a CASPIR/SHOW=CURRENT command,
the current A-B difference is displayed in the Run Display. If the
SHOW parameter has been set to MEAN with a CASPIR/SHOW=MEAN
command, the average of the accummulated difference images is
displayed in the Run Display.