RASTER

 

           RASTER Size_x Res_x [Size_y  Res_y]  [/REFERENCE  Off1  Off2
 [System]] [/ON_OFF N] [/TIME Time_on Time_off]
      Select a raster map observation for line  backends  and  provides
 the  possibility  of  several  ON's per OFF, thus using telescope time
 most efficiently.
                    ----------> CAUTION <----------
 This command is a facility provided only for very short  integrations.
 It  should be used only if the weather is extremely good, and requires
 good stability of the receivers.  Your observing goals may  be  better
 reached  by  using the loop facility of OBS (FOR command from language
 SIC) which allows for flexible procedures.
                    -------------------------------
      The map orientation (BASIS  or  HORIZONTAL)  is  defined  by  the
 default coordinate system (SET OFFSET command)
      The size of the map is Size_x by Size_y, in current  angle  units
 (SET  ANGLE  command).   The resolution is Res_x by Res_y (same units)
 Size_y and Res_y default respectively to Size_x and Res_x.  The map is
 centered on the current offsets (OFFSET command)
      The reference position (off-position) is  offset  by  (Off1,Off2)
 from  the  source position.  Current angle units are used.  The System
 argument can be given to indicate the coordinate system used  for  the
 reference position and can be BASIS or HORIZONTAL; if not present, the
 default coordinate system defined  by  SET  OFFSET  is  used.   (Note:
 switching  in  HORIZONTAL  mode may decrease the intensity of baseline
 ripples.)
      The number N of On points per Off point is defined by the /ON_OFF
 option.   More than 2 or 3 is usually unrealistic.  Note also that the
 raster duration should not be too long for the calibration  to  remain
 valid.
      The subscan length can be specified separately  for  On  and  Off
 subscan  using the /TIME Time_on [time_off] option.  Time_off defaults
 to Time_on*(N)**0.5 (optimal signal to noise), but may be  rounded  to
 give an integer number of dumps (Time_on/2).