Processing P40 data with PIA - staring or chopping mode

(PIA 7.3.2, March 1999)

This is a step-by-step guide illustrating how to reduce a P40 data (staring or chopping mode) from ERD to AAP (equivalent to the AAR, Auto Analysis Result, from the pipeline) with the PIA. The default PIA parameter setting and default flux calibration table are used. If you need more details, please refer to the PIA manual and the IDUM, ISOPHOT Data Users Manual, or contact ISO helpdesk at IPAC.

Select and read Data

Make sure the PIA paths are set up correctly.
[ ] (Top Window) Customize -> PIA paths

Select the P40 ERD file and read it into the PIA buffer. The P40 ERD files have PSER prefix (both PHT-SS and SL measurements are together in one file).
    [ ] (Top Window) Files -> Files Manager
    [ ] Select File Type: ERD and Detectors: SS/SL using the two filter windows.
    [ ] The P40 ERD file name(s) should appear in the "Files" subwindow. If not,
         you can click on one of the subdirectory names shown in the
         "Subdirectories" subwindow to see if you can navigate to the desired file.
         Once you have located the correct file in the "Files" subwindow, click on
         the file name.
    [ ] Click on "Read File" button to read the selected file into the PIA buffer.
    [ ] Option: Click on "Show Header" button to view or to print the ERD FITS
         header.

Select an ERD measurement for processing.
    [ ] (Top Window) Buffers -> Buffers Manager
    [ ] Select Data Type: ERD and Detectors: SL/SS. All the measurements in the
         selected category should show up in the "measurement" window. Usually,
         there are 2 measurements: the first one is a "pseudo" dark measurement
         and the 2nd one is the real observation. Hence, click on the 2nd
         measurement.
    [ ] Click on the "Plot & Reduce Data" button to bring up the PIA ERD window.
    [ ] Option: Click on the "Show..." button in the Buffers Manager window to
         view FITS header, Compact Status or even the data values themselves.

Reduction of the ERD (to SRD)

The PIA ERD window shows the read-out ramps as a function of time for 4 out of the 128 detector pixels. Some readouts are masked out (shown as red x's) by default.
    [ ] Option: Use the "Zoom & Print" button to blow up the displayed pixel in
         order to see individual ramps more clearly or to print the display on the
         laser printer. This option is available on all reduction levels.
    [ ] Option: Use the "Selection" button to change the read-out discarding
         scheme from the default.
    [ ] (ERD Window) Correction -> Read-out simple deglitching
         (Non-linearity correction is not available for PHT-S at this time, but it
         is small.)
    [ ] (ERD Window) Correction -> 2 Threshold deglitching
    [ ] (ERD Window) Process Meas. -> Fit Ramps (1st order polynomial)
         This fits a slope to each integration ramp and brings up the SRD window.
         You also have the option of dividing the ramp into a desired number of
         subdivided ramps using the fourth choice of the Process Meas.

Reduction of the SRD (to SCP)

The PIA SRD window displays the time series of the ramp slopes for 4 out of the 128 detector pixels. Again, the masked out slopes by default are shown in red color.
    [ ] (SRD Window) Correction -> Reset interval correction
    [ ] (SRD Window) Correction -> Deglitching
         This is to filter out badly deviated slopes.
    [ ] (SRD Window) Correction -> Dark Current Subtraction
         This is to subtract out the default orbital position dependent dark
         current.
    [ ] Option: (SRD Window) Selection -> Discard Signals
         Use this to change the discarding scheme from the default. If changes
         are made, do apply the deglitching correction again.
    [ ] Option: (SRD Window) Data -> Save (to PIA internal file)
         This is to save the SRD result into a disk file.
    [ ] (SRD Window) Process -> no drift handling (Option: with drift handling)
         This will bring up the SCP window.

Reduction of the SCP (to AAP)

The PIA SCP window shows the average slopes per chopper plateau as a function of time. This data reduction step depends on whether your observation is chopped or staring.

In the case of a chopped observation:

    [ ] (SCP Window) Process -> Background Subtraction (within measurement)
         This brings up two windows: PIA Background Subtraction Menu and a graphic
         window displaying the "grand average signal" per chopper step.
    [ ] Usually, one needs only to click on the "OK" button in the Menu window.
    [ ] Click on the "Subtracted meas -> buffer" button to write the
         sky-subtracted spectrum to the SCP buffer.
    [ ] Now let's display the sky-subtracted spectrum. Exit out of all the Data
         Display windows, then go to the Buffer Control Panel and select SCP and
         SL/SS for the Data Type and Detectors respectively. Select the
         background subtracted data and click on the "Plot & Reduce Data" button
         to bring up the PIA SCP window.
         Caution: avoid using the Load button to display the subtracted data
         because this makes the appropriate Process option (Chopped SPRF)
         unavailable.
    [ ] (SCP Window) Process -> Power Calibration --> Chopped SPRF (only for SL)
         This will bring up the AAP window.
    [ ] Option: you can save the SCP result of sky-subtracted spectrum by clicking
         in the SCP window "Data --> Save --> To a PIA Internal File."

In the case of a staring observation:

    [ ] (SCP Window) Process -> Power Calibration --> Default Responses (orbital
         dep.) --> Perform it. This will bring up the AAP window.
    [ ] Option: you can save the SCP result of sky-subtracted spectrum by clicking
         in the SCP window "Data --> Save --> To a PIA Internal File."

    Hint: if you have a sky measurement from another observation, you can do a
    sky subtraction from the spectrum of the current staring observation at
    the AAP level by click there "Process --> Background Subtraction --> another
    measurement." Make sure that you loaded the AAP result of the sky measurement.

Note: This data reduction of SCP to AAP actually produces the intermediate SPD result which is not displayed automatically. You can however display the SPD result using the buffer manager in the conventional way.

Examine the AAP result with Astrophysical Applications

The AAP (Astrophysical Applications product) result is comparable to the pipeline AAR (Automatic Analysis Result data). The AAP result is displayed in two windows, one for the SS part (2.5 to 5 microns) and one for the SL part (6 to 11.6microns) of the spectrum. These spectra can be best examined using "Astrophysical Work" available in the PIA top window.

    [ ] Option: If you have not save the SPD result, you may want to save the
         AAP result now. To do so, click "Data --> Save --> PIA Internal File"
         in each of the AAP windows displayed.
    [ ] (Top Window) Buffers -> Astrophysical Work
         An Astrophysical Applications Menu window appears on your screen.
    [ ] Select the "Spectro-Photometry" function.
         This brings up a window called PIA Spectro-photometry.
    [ ] (Spectro-photometry window) Click on the "File" button and then
         "Select measurement." Choose the measurement to be loaded.
    [ ] (Spectro-photometry window) Click on the "Plot" button to plot the
         spectrum in a number of different ways. Use the "new" option for
         the spectrum plot.

    Hint: To display the SS and SL parts of the spectrum together, first plot
    one as described above and leave the plot on. Then read the other part into
    Astrophysical Work, but choose "Overplot --> Synchronized" (instead of "New")
    to display the two parts together.

Last update: July 1999