Defringing GUI Interface for LIA 8.

User Guide.



 
 
 

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:

0. Introduction.

1. Definitions and requirements.

2. Running the program.

3. Recipe for L01 AOT data.

4. Recipe for L03 AOT data.

5. Recipe for L04 AOT data.

0. Introduction.

 
Sinusoidal fringes are observed in the LWS spectra of extended sources and off-axis point sources.
In both grating and Fabry-Perot observations, they arise due to the interference between two beams propagating in the instrument with a time delay between the beams.
The algorithm.
 
The defringing routine uses an algorithm developed for the detection of periods in spectroscopic binaries by Chris Lloyd at RAL.
The original routine written for ISAP solves for the period, phase and wavenumber dependent amplitude of a sine wave fitted to the data from a single detector of an L01 AOT observation.
More details of the algorithm used follows in later sections.

1. Definitions & Requirements.

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. 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,

3.  L01 AOT Recipe.
 
 

The example below shows fringed L01 data.

 

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 below about 2.5 allow the floating period to vary too much, the fit is less stringent and some very strange results can occur
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.
 
 


 
 

 

Once the GUI interface appears (as above), you will have several options.
 
First, select a detector, and remove any lines or spikes (e.g. as at 122 mm in the figure above) using the right mouse button.
 
From studying the fringed data, you must make an intelligent guess as to the period of the fringing.   Sometimes the period is very evident, sometimes it is more difficult to establish.   Unless you are 100% sure of the period (e.g. from having defringed the same data on a previous occasion), leave the 'Float period' button ON.    The less certain you are of the period, the smaller the value of nsig needs to be, as this value allows the program to search for a period to fit to the data.
 
Small values let the period vary more, giving you more flexibility, but values below 2.0 can sometimes give strange, unreliable results.
 
Values above 6.0 can be too restrictive and are not useful.
 
A suggested sensible range of values would be 2.5 (for a first guess) through to 4.5 (for a final guess).
 
If the program cannot find a good fit to the data using the values that you have selected, then a dialog box will appear asking you to try changing the input values and trying again.
 
Point source or extended source?
Next, select either a point source (default) or an extended source.   An extended source is one which is greater than 20 arcsecs.
Think carefully about your choice of object type!
 
With fully extended line AND continuum emission or an off-axis point source with no significant extended continuum, you should DIVIDE out the fringe.
 
Y_OUT = Y * MODF
 
MODF is the normalized fringe,
 
MODF = (FITTED CONTINUUM)/(FITTED CONTINUUM + FRINGE)
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.
 
 
 
 

4.  L03 AOT Recipe.

 

The example below shows fringed L03 data.

 
 

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)

values below about 2.5 allow the floating period to vary too much, the fit is less stringent and some very strange results can occur
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.
 
 


 
 

Once the GUI interface appears (as above), you will have several options.
 
First, select a mini-scan, and remove any lines or spikes (e.g. as at 57.33 mm in the figure above) using the right mouse button.
 
From studying the fringed data, you must make an intelligent guess as to the period of the fringing.   Sometimes the period is very evident, sometimes it is more difficult to establish.   Unless you are 100% sure of the period (e.g. from having defringed the same data on a previous occasion), leave the 'Float period' button ON.    The less certain you are of the period, the smaller the value of nsig needs to be, as this value allows the program to search for a period to fit to the data.
 
Small values let the period vary more, giving you more flexibility, but values below 2.0 can sometimes give strange, unreliable results.
 
Values above 6.0 can be too restrictive and are not useful.
 
A suggested sensible range of values would be 2.5 (for a first guess) through to 4.5 (for a final guess).
 
If the program cannot find a good fit to the data using the values that you have selected, then a dialog box will appear asking you to try changing the input values and trying again.
 
Point source or extended source?
Next, select either a point source (default) or an extended source.   An extended source is one which is greater than 20 arcsecs.
Think carefully about your choice of object type!
 
With fully extended line AND continuum emission or an off-axis point source with no significant extended continuum, you should DIVIDE out the fringe.
 
Y_OUT = Y * MODF
 
MODF is the normalized fringe,
 
MODF = (FITTED CONTINUUM)/(FITTED CONTINUUM + FRINGE)
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.
 
 

5.  L04 AOT Recipe.

 

The example below shows fringed L04 data.

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)

values below about 2.5 allow the floating period to vary too much, the fit is less stringent and some very strange results can occur
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.

Once the GUI interface appears (as above), you will have several options.
 
First, select a line, and remove any lines or spikes using the right mouse button.
 
From studying the fringed data, you must make an intelligent guess as to the period of the fringing.   Sometimes the period is very evident, sometimes it is more difficult to establish.   Unless you are 100% sure of the period (e.g. from having defringed the same data on a previous occasion), leave the 'Float period' button ON.    The less certain you are of the period, the smaller the value of nsig needs to be, as this value allows the program to search for a period to fit to the data.
 
Small values let the period vary more, giving you more flexibility, but values below 2.0 can sometimes give strange, unreliable results.
 
Values above 6.0 can be too restrictive and are not useful.
 
A suggested sensible range of values would be 2.5 (for a first guess) through to 4.5 (for a final guess).
 
If the program cannot find a good fit to the data using the values that you have selected, then a dialog box will appear asking you to try changing the input values and trying again.
 
Point source or extended source?
 
Next, select either a point source (default) or an extended source.   An extended source is one which is greater than 20 arcsecs.
Think carefully about your choice of object type!
 
With fully extended line AND continuum emission or an off-axis point source with no significant extended continuum, you should DIVIDE out the fringe.
 
Y_OUT = Y * MODF
 
MODF is the normalized fringe,
 
MODF = (FITTED CONTINUUM)/(FITTED CONTINUUM + FRINGE)
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.