It is assumed that the source is centred at the reference point of the supplied observations.
An IP model gives the normalised Q and U values (Qn and Un) with respect to focal plane Y axis, at any point on the sky, as functions of elevation. The correction is applied as follows:
Q_corrected = Q_original - IQn U_corrected = U_original - IUn
" is the total intensity at the same point on the sky as Q_original and U_original. All (Q,U)
values use the focal plane Y axis as the reference direction.
" IP model is as follows (
" = elevation in radians):
p1 = A Bel Celel Qn = Ip1cos(-2(el-D)) Un = Ip1sin(-2(el-D))
It is parameterised by four constants A, B, C and D, which are calculated by this script. It represents an instrumental polarisation that varies in size with elevation but is always at a fixed angle (D radians) from the elevation axis.
The PL2 model replaces the earlier PL1 model. The difference is that the D constant was fixed at zero in the PL1 model.
"is created in the current directory. This is a table containg columns of the geometric properties of the polarised intensity beam in each observation. The header for this file contains the parameters of quadratic fits to these properties, which are used within pol2scan. 
" : No screen output is created
" : Only critical messages are displayed such as warnings.
" : Extra messages indicating script progress are also displayed.
" : Extra messages are also displayed describing each atask invocation. Lines starting with
indicate the command name and parameter values, and subsequent lines hold the screen output
generated by the command.
" : Extra messages are also displayed containing unspecified debugging information. In
addition scatter plots showing how each Q and U image compares to the mean Q and U image are
displayed at this ILEVEL.
In adition, the glevel value can be changed by assigning a new integer value (one of starutil.NONE,
starutil.CRITICAL, starutil.PROGRESS, starutil.ATASK or starutil.DEBUG) to the module variable
", where command is the name of the executing script (minus any trailing
"suffix), and will be created in the current directory. Any file with the same name is over-written. The script can change the logfile if necessary by assign the new log file path to the module variable
". Any old log file will be closed befopre the new one is opened. 
", and each observation should have a separate subdirectory within its UT date subdirectory. Any new Q/U/I maps created by this script are placed in this directory. If null (!) is supplied, the root directory containing the Q/U maps is placed within the temporary directory used to store all other intermediate files. [!]
"function. The accepted values are the list defined in SUN/104 (
", etc). [
", where ut is the 8 digit UT date (e.g.
") and obs is the 5 digit observation number (e.g.
"). Blank lines and lines starting with
"are ignored. The raw data for all observations is expected to reside in a directory given by environment variable
", within subdirectories with paths of the form: $SC2/[s4as8a]/20150918/00056/ etc. The choice of
"is made on the basis of parameter WAVEBAND.
", and each observation should have a separate subdirectory within its UT date subdirectory. Any new Q/U/I time streams created by this script are placed in this directory. If null (!) is supplied, the root directory containing the Q/U time streams is placed within the temporary directory used to store all other intermediate files. [!]