What this User Guide is:
What this User Guide is not:
The recipes are worked examples of real data reduction of fringed LWS data, for each AOT for which defringing is available; it covers some simple aspects of reducing the data. Where you require further information which is not covered here, we encourage you to check the LWS and LIA FAQs; should your question remain unanswered, please contact us at isouk@rl.ac.uk.
Contents:
1. Definitions and requirements.
More details of the algorithm used follows in later sections.
The routine which is used in ISAP for L01 data has been adapted and extended to run as a stand-alone GUI interfaced post-processing routine for THREE different AOTs (L01, L03 and L04), and is run from a single line command from the ‘isap com’ IDL environment.
isap com - command which runs IDL linking in ISAP and LIA procedures
L01 AOT - Grating (i.e. low resolution) observation covering the whole LWS wavelength range across different detectors
L03 AOT - Fabry-Perot (i.e. high resolution) set of mini-scan observations covering a certain wavelength range
L04 AOT - Fabry-Perot (i.e. high resolution) scan across a line over a very limited wavelength range (grating is fixed)
With this GUI routine, the facility now exists to defringe L01 grating AOT data AND now also Fabry-Perot L03 and L04 AOT data.
ALL you require is a FITS file which needs to contain the averaged data for any AOT (except L02) which requires defringing.
Note that the program defringes by detector (for L01 AOT) or by mini-scan (for L03 AOT), or by line (for L04 AOT), so that your averaged data should NOT have been averaged across detectors (for L01 AOT), or across mini-scans (for L03 AOT), or lines (for L04 AOT). This is because the algorithm is applied to each individual detector/mini-scan/line in turn.
2. Running the program.
The defringe program is very easy to run.
Enter the ‘isap com’ environment, thus:
$ isap com
ISAP> defringe,[nsig=],[period=],[floatp=],infile=,[outfile=]
where,
nsig = no. of sigma for rejection of fitted points [optional]
period = period of fringe (cm^-1) [optional]
floatp = boolean for floating value of the period 0: Off (default) 1: On [optional]
infile = FITS file to read from (including full path, in single quotes) [mandatory]
outfile = FITS file to write to (including full path, in single quotes) [optional]
First you need to decide what parameters you will first try when you run the progam.
The period of the fringing in L01 data tends to be around 3 cm^-1.
The default values (i.e. if no values are specified on the command line) are:
nsigma = no. of signal rejection (e.g. 3.0)
values above about 6.0 restrict the floating period too much and has much the same result as setting floatp to 0
period = period used (e.g. 3.0 cm^-1)
i.e. the periodicity of the fringe.
The only real way to guess this is by carefully studying the data by eye.
floatp = float period OFF (0: default) or ON (1)
Use your best guess with FLOATP=1 and nsig=3 or slightly less, and, if you're having a really good day then you will get a good fit straight away!
Interfacing with the GUI.
If, on the other hand, you have a point source emitting the lines embedded in an extended (fringed) continuum region then you should SUBTRACT the fringe.
Y_OUT = Y - FRINGE
As yet, nothing has been developed for a source in between these states!
Undoing the defringing.
If you are not happy with the outcome, you can press the 'Undo Defringe' button, which restores the original dataset for that detector, and you can start again, if necessary.
Once you press 'Exit', any data that has been defringed will be written into the outfile FITS file, thereby overwriting the original data.
Any un-defringed data will be written back unchanged.
Producing hard copy.
At any stage, you can choose to produce a hard copy of the on-screen plot.
Simply click on the 'Hard Copy' button and a dialog box will appear with a default title and postscript file (hardcopy.ps) to write the plot to, which can be easily renamed. If you want a hard copy of the overplotted fringed and defringed data, then it would be a good idea to click the radio button to select a colour plot, as a B&W (default) plot may look confusing.
Saving the results.
After defringing, when pressing the 'Exit' button, the routine writes out any data that has been defringed plus the remaining, untouched data, into a user-nominated FITS file. The FITS file has comments added to the effect that a sub-set of the data has been processed by a defringing algorithm, and as such should be treated with caution.
Note, however, that pressing 'Exit' when no outfile was specified has the same result as pressing 'Quit', both of which result in no outfile being created.
First you need to decide what parameters you will first try when you run the progam.
The period of the fringing in L03 data tends to be around 0.1 cm^-1.
nsigma = no. of signal rejection (e.g. 3.0)
period = period used (e.g. 0.1 cm^-1)
i.e. the periodicity of the fringe.
The only real way to guess this is by carefully studying the data by eye.
floatp = float period OFF (0: default) or ON (1)
Use your best guess with FLOATP=1 and nsig=3 or slightly less, and, if you're having a really good day then you will get a good fit straight away!
Interfacing with the GUI.
If, on the other hand, you have a point source emitting the lines embedded in an extended (fringed) continuum region then you should SUBTRACT the fringe.
Y_OUT = Y - FRINGE
As yet, nothing has been developed for a source in between these states!
Undoing the defringing.
If you are not happy with the outcome, you can press the 'Undo Defringe' button, which restores the original dataset for that mini-scan, and you can start again, if necessary.
Once you press 'Exit', any data that has been defringed will be written back into the outfile FITS file, thereby overwriting the original data.
Any un-defringed data will be written back unchanged.
Producing hard copy.
At any stage, you can choose to produce a hard copy of the on-screen plot.
Simply click on the 'Hard Copy' button and a dialog box will appear with a default title and postscript file (hardcopy.ps) to write the plot to, which can be easily renamed. If you want a hard copy of the overplotted fringed and defringed data, then it would be a good idea to click the radio button to select a colour plot, as a B&W (default) plot may look confusing.
Saving the results.
After defringing, when pressing the 'Exit' button, the routine writes out any data that has been defringed plus the remaining, untouched data, into a user-nominated FITS file. The FITS file has comments added to the effect that a sub-set of the data has been processed by a defringing algorithm, and as such should be treated with caution.
Note, however, that pressing 'Exit' when no outfile was specified has the same result as pressing 'Quit', both of which result in no outfile being created.
First you need to decide what parameters you will first try when you run the progam.
The period of the fringing in L01 data tends to be around 3 cm^-1.
nsigma = no. of signal rejection (e.g. 4.0)
period = period used (e.g. 0.1 cm^-1)
i.e. the periodicity of the fringe.
The only real way to guess this is by carefully studying the data by eye.
floatp = float period OFF (0: default) or ON (1)
Use your best guess with FLOATP=1 and nsig=3 or slightly less, and, if you're having a really good day then you will get a good fit straight away!
Interfacing with the GUI.
If, on the other hand, you have a point source emitting the lines embedded in an extended (fringed) continuum region then you should SUBTRACT the fringe.
Y_OUT = Y - FRINGE
As yet, nothing has been developed for a source in between these states!
Undoing the defringing.
If you are not happy with the outcome, you can press the 'Undo Defringe' button, which restores the original dataset for that line, and you can start again, if necessary.
Once you press EXIT, any data that has been defringed will be written back into the outfile FITS file, thereby overwriting the original data.
Any un-defringed data will be written back unchanged.
Producing hard copy.
At any stage, you can choose to produce a hard copy of the on-screen plot.
Simply click on the 'Hard Copy' button and a dialog box will appear with a default title and postscript file (hardcopy.ps) to write the plot to, which can be easily renamed. If you want a hard copy of the overplotted fringed and defringed data, then it would be a good idea to click the radio button to select a colour plot, as a B&W (default) plot may look confusing.
Saving the results.
After defringing, when pressing the 'Exit' button, the routine writes out any data that has been defringed plus the remaining, untouched data, into a user-nominated FITS file. The FITS file has comments added to the effect that a sub-set of the data has been processed by a defringing algorithm, and as such should be treated with caution.
Note, however, that pressing 'Exit' when no outfile was specified has the same result as pressing 'Quit', both of which result in no outfile being created.
Document created and maintained by: Gerard Hutchinson. ISO Data Centre. Rutherford Appleton Laboratory.