Processing Data from a Staring Observation with C200 in P22, P37/38/39

(PIA 7.3.2, March 1999)

This is a step-by-step example illustrating the basic data reduction with PIA from ERD to AAP (equivalent to the AAR, Auto Analysis Result, from the pipeline) of a staring observation with the 4x4 C200 array detector in one of the following AOTs: P22, P37, P38, and P39.  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 P22/P37/P38/P39 ERD files and read them into the PIA buffer.  The C200 data files have P2ER prefix.  In the case of sparse map data chain of P37/P38/P39, the FCS measurements are contained in P37 and P39 only, and one should consider reading all of them into the PIA buffer.
    [ ]  (Top Window) Files  ->  Files Manager
    [ ]  Select File Type: ERD and Detectors: C200.
    [ ]  The 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

Normally, one reduces the FCS measurement(s) first then the astronomical data.  In the case of P37/38/39, this means that one processes both of the two FCS measurements first.  Note that the steps from ERD to SCP are the same regardless of whether the measurement being processed is FCS or astronomical.

Select an ERD measurement for processing.
    [ ]  (Top Window) Buffers  ->  Buffers Manager
    [ ]  Select Data Type: ERD and Detectors: C200.  All the measurements in the
         selected category should show up in the "measurement" window.  For P22,
         there is only one FCS measurement.  There should be two FCS measurements
         (one from P37 and the other from P39).  Usually, 2 or more positions are
         observed using one or more filters.  Select the measurement by clicking
         on it.
    [ ]  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 all 4 pixels of C200 detector.  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  ->  Non-linearity
    [ ]  (ERD Window) Correction  ->  Read-out simple deglitching
    [ ]  (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.

Reduction of the SRD (to SCP)

The PIA SRD window displays the time series of the ramp slopes for all 4 pixels of C200 detector.  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
    [ ]  (SRD Window) Process  ->  no drift handling (Option: with drift handling)
         This will bring up the SCP window.
    [ ]  Option: (SRD Window) Data  ->  Save (to PIA internal file)
         This is to save the SRD result.

Hint: it may be a good idea to process all the measurements in the same AOT to the SCP level before proceeding to the SPD level.

Reduction of the SCP (to SPD)

The PIA SCP window shows the average slopes per chopper plateau as a function of time.  This step is slightly different for a FCS measurement than for an astronomical measurement:

If this is a FCS measurement:
    [ ]  (SCP Window) Correction  ->  Straylight subtraction (This correction
         is still uncertain, at a level of up to a few percent for C200)
    [ ]  (SCP Window) Process  ->  Responsivity Calculation
         Click on the "ACCEPT" button for the average responsivity value from FCS1.

If this is an astronomical measurement:
    [ ]  (SCP Window) Process  ->  Power Calibration
         If this is a P22 measurement, select either default responsivity or
         the actual FCS for power calibration; if this is a P37 or P38 or P39,
         one can select to use the last Responsivity calculated from a FCS
         measurement (Actual Responses), or to use the average (Average Responses)
         or a linear interpolation in time between the two FCS measurements
         (Interpolate Responses).  In the last two cases, do the following steps:

         Select the FCS measurements on the pop up window and then click the "Ok"
         button.  When the PIA Response Menu window appears for each FCS
         measurements, then click on the "ACCEPT" button to choose the average
         responsivity value from FCS1.  This converts V/s to watts and pops up
         an AAP window.

Hint: in the case of P37/38/39, by concatenating the SRD or SCP results of all the measurements (including the 2 FCS measurements) in the same AOT, one may better judge which of the following is a better way to do flux calibration: interpolation, averaging or simply using only one of the FCS measurements.

Examine the AAP results

This step applies only to an astronomical measurement.  One might want to reduce all measurements (e.g., both on-source  and off-source data) to the AAP level before doing this step.
    [ ]  Go back to the Buffer Control Panel and, click on one of the AAP entries.
    [ ]  Plot this data by clicking on the "Plot & Reduce Data" button on the
         Buffer Control Panel.  The AAP window should appear.
    [ ]  (AAP Window) Array  ->  Images
         This displays the mean fluxes at all 4 pixels.  Make sure to click on
         the "Skirt" button at the bottom left on the pop-up display to see the
         flux scales.  Ideally, the fluxes at all 4 pixels should be at roughly
         the equal level.

Hint: If this displayed measurement is the on-source measurement, then do a background subtraction as follows:  [before doing so, you may also want to examine the 4 pixel levels of the off-source measurement as outlined above]

    [ ]  (AAP Window) Process  ->  Background Subtraction (another measurement)
    [ ]  Select the off-source measurement from the pop-up window.
         The subtracted AAP result is stored in the PIA butter.
    [ ]  Option: Save the sky-subtracted result into a disk file of PIA internal
         format by using the "Save... (Internal Save File)" button on the Buffer
         Control Panel.

Deriving the Total Flux Density or Average Surface Brightness

    [ ]  (Top Window) Buffers  ->  Astrophysical Work
    [ ]  Select "Multi-Filter Photometry for Point Sources" or "Multi-Filter
         Photometry for Extended Sources."
    [ ]  Select by clicking all the sky-subtracted measurements that you want to
         display together.
    [ ]  Click on "Select all" button to use all 4 pixels, then press the "Ok"
         button.  This brings up the colour correction window.
    [ ]  Click the "No Colour Corr" next to the "Ok" button.

Last update: 5 March 1999