Manuals : ISOPHOT Interactive Analysis (PIA) : PHT Interactive Analysis User Manual - (V9.0)

PHT Interactive Analysis User Manual - (V9.0)

2.2) Processing Data with PIA - A Guided Tour

This chapter serves as an aid to guide you through a PIA sample session step by step. The emphasis is on the overall sequence of the steps and their connection, therefore details of the processing and interface at each step are described only as far as necessary. For a detailed description of the interface and possible actions at each of the steps, please refer to the material on the windows (chapter 3) or processing (chapter 5) in this manual. Note that the PIA graphical user interface generally offers several options for which data reduction steps can be performed at any given time. It is also possible to display intermediate results of the current reduction at any time, or to reduce several observations simultaneously. However, a straightforward reduction of an ISOPHOT observation can, in general, be performed as a standardised sequence of steps.

The reduction of ISOPHOT data with PIA consists of the following overall parts:

  1. Start PIA.
  2. Select data, i.e files (OLP files in FITS format, internal PIA produced files in IDL/XDR format), or already read data residing on internal memory.
  3. Analyse and process the data. There are two kinds of data:
    4. Note: PHT-S does not provide an FCS measurement.

Some Preliminary Notes

Installation and Set-up: We assume that PIA is already installed properly on your account. If this is not the case please refer to Appendix D - Installing the PIA Software.

Note that the filenames on the CDs are not according to the conventions for the pipeline and PIA. They are split into a directory part named after the TDT+OSN number and a file name part, this is because of the restriction of the ISO standard under which the CDs are written. You will need to ensure that your data have been renamed according to the standard file naming conventions (consult the PIA Homepage: http://general-tools.cosmos.esa.int/iso/manuals/PHT/pia/pia.php for filenames converters). You will probably find it more convenient if the raw data files corresponding to one proposal are all stored in the same location on disk.

Hints:

The UNIX window from which you launch PIA serves as a message output console for PIA. This console will be running an IDL session. Its last line should be visible all the time (and not be hidden by other windows). Particularly at the beginning you may need to watch it in order to see whether PIA performs actions and which problems arise. From PIA V7.0 on a new IDL feature is used, which makes it possible to use this window as a command window. Because of this you don't need to leave PIA for executing IDL commands, or even PIA commands, which can be sent from the command window (details on accessing PIA buffers are given in 'Advanced PIA use - ...')

In the case of a crash you may refer to the apppendix F on trouble shooting in this manual for more detailed information. In many cases, however, it is easy to continue the session without loss of data.

Conventions:

In this guided tour, clickable buttons on the interface and items to be selected from menus and their submenus will be shown in bold, fixed typeface. A submenu often appears when a main menu button is pushed (clicked on with the mouse).

Starting PIA

Now let us start PIA: Once you have started PIA the first you will see is a message window: Welcome to the PHT-Interactive Analysis.

Then you will see a window entitled: Welcome to PIA, with information about the development of PIA. Click:

Acknowledged
in this window and the PIA Top Window (section 3.1) shown in Figure 1 will be displayed.

FIGURE 1: The PIA Top Window

Select Data

One basic feature of PIA is that the programme works with "the buffer"; temporary internal storage in IDL. For PIA this buffer is actually splitted into several buffers, one for each reduction level (e.g., the ERD buffer, the SRD buffer, etc.). The data are stored in the appropriate buffer at each level of data reduction and remain in memory until PIA is exited or the buffers are explicitly deleted. Each buffer can contain a number of observations from different input data files, so it is possible to process several files and measurements simultaneously or combine the results of different observations. The contents of a buffer can be written out to a data file per measurement if you want to retain them after the PIA session ends.

If you have more than one observation, you will need to know the TDT (Target Dedicated Time) and OSN (Observation Sequence Number) of the observation you want to load into PIA; the rest of the filename can be reconstructed by PIA based on the level of data and detector. For example, PIA will find the file PPER01301401.FITS if you tell it you want to work on ERD for a PHT-P detector. The TDT+OSN number, here= 01301401 uniquely identifies the observation. The first 3 digits are the Revolution number, the next 3 digits a sequence number and the last two the OSN. the rest will be found by PIA. File name conventions are discussed in the Appendix E.

The data selection consists of the following steps:

  1. Set filetype and detector
  2. Select a file
  3. View the file header (optional)
  4. Read the file into the buffer
  5. Select a measurement within the file
  6. View the compact status for the selected measurement (optional)
The file header is the main FITS header and contains, e.g. the Proposal ID, pointing information, and information about the performed processing steps by PIA (the lines beginning with PR...) The compact status contains the measurement configuration, i.e. information about the time, chopping parameters, filters, apertures etc.). More details about the contents of the pipeline files can be found in the IDPD or the IDUM, which were distributed on the CDROM along with the data.

All these steps can be performed interactively by using the Files Manager and the Buffers Manager:

1. Using the Files Manager and the Buffers Manager

From version 4.7 on PIA offers a compact way to access files and internal buffers:

1. The Files Manager

Select the following menu and submenu from the PIA Top Window: A new window appears as shown in Figure 2.

FIGURE 2: The PIA Files Manager window

Basically the window is divided into three rows:

  1. The control row: it contains lists for choosing detector and level, file types and corresponding paths to be used.
  2. The files management area: it contains a number of selectable lists and buttons for identifying and reading a file or several files.
  3. The message box.
In this window you perform the following steps:

Control row:

  1. Select a File-Type and Detector (e.g. ERD and P1,P2,P3 as preselected):

    2. Click explicitly with the left mouse button onto the selected items.
     
  2. At the options "Select Files from":

    3. Choose option: Pipeline FITS

    Then in the files management area the corresponding list of available files is displayed.

    Note: The two alternative options "PIA FITS" and "Internal Save File" are for the reloading of your individually-stored intermediate results.

Files management area:
  1. Select a File (e.g. PPER01301402.FITS):

    2. Click explicitly with the left mouse button onto the selected file.
     
  2. Press the action button: "Read File"

    3. The selected file is then read into the buffer. (Note: it will be read each time the button is pressed, occupying new space in the buffer.)

    Note: There is also the option to read multiple files, which works as follows:
    Select a file and then press the action button "Add file" (which appears by the multiple files option). The name of the chosen file appears in the list "Selected Files for Reading". After several selections press the action button "Read All" and all the selected files are read into the buffer. The possibility of adding all files of the chosen type at once int the selected files for reading is also given.

Message box:

With every file that is read into the buffers a message will appear confirming this action.

2. The Buffers Manager:

FIGURE 3: The PIA Buffers Manager window

Reduction of the ERD (to SRD)

The Edited Raw Data (ERD, the detector read-out values in V), are examined, corrected for artifacts and processed into the Signal per Ramp Data (SRD,the slope of each ramp in V/s).

Both FCS measurements and astronomical data require the same procedure at this stage of data reduction.

When you have selected a measurement and chosen "Plot and Reduce Data", you will see the "PIA ERD Window" as shown in Figure 4:

FIGURE 4: The ERD Window for a P3 measurement

This Window is divided into three rows.

  1. The upper row contains some general control buttons and information.
  2. The middle row shows four plots with associated buttons above and below the plot which affect that plot.
  3. The lower row contains the menu buttons which perform the actual processing on the whole measurement.
(Note: you may see only 3 plots. If this occurs and the second but last button on the bottom row reads "4 Plots", then your display doesn't have enough pixels to accomodate the full PIA display. This should not prevent you from working, but may be annoying.)

Note: There is a slight difference in the way PIA displays information (when opening the main windows) for single pixel detectors (P1, P2, P3) and for array detectors (C100, C200, PHT-S):

For the single detectors the plots show four different types of information for the single pixel, while for the array detectors all plots show read-out values against time for different pixels. It is easy to modify the content of the plots, both the pixels displayed and the quantity plotted. For detailed information about these features please refer to the chapter ERD Window in the reference part of the PIA User Manual.

Let us have a closer look at the middle row of Figure 6 going from right to left: (Note that in this illustration the symbols are quite large, so neighbouring points tend to blend together; this will improve in the zoomed plots later.)

There are two basic features of the middle row which you will use frequently:
  1. Changing the contents of the Plots: The menu bar just above each plot allows you to change the content of the plot, e.g. read-out values/time or chopper position/time and so on. The descriptions indicate the content of the actual plot.

    2.  
  2. Zooming in: The menu button "Zoom & Print" just below each plot allows you to inspect the plot in detail via the PIA Xplot Window (section 3.4.1). You can use the PIA_Xplot Window to zoom in on your data (choose "New") or to plot one type of information on top of another (Submenu "Overplot"). For example, to plot the chopper plateaux on top of the read-out values, choose PIA_Xplot with the "New" Option. Then display the chopper plateux and choose PIA_Xplot with the "Overplot, new y-axis" option ("Overplot, same y-axis" would re-scale the data to the chopper-plateau y-axis).
Now let's process the ERD. Although there are many possible sequences of actions, we will concentrate on the most necessary ones in an appropriate order:
  1. Discard Read-Out Values:

    2. Press the menu button "Selection" (submenu "Discard Read-Outs"). This brings up the Read-Out Selection Window which is used to flag selected read-outs to exclude them from further processing. If you like, you can modify the parameters to see the effects.
     
  2. Correction for Saturation (Set allowed dynamic range):

    3. The correction for saturated read-outs (i.e., discarding them from further processing) is always active and performed automatically. The data which will be discarded are marked with red crosses in the plots. If you like, you can modify the parameters to see the effect:

    Press the menu button in the lower row labeled "Correction" and choose "Change Saturation Parameters" from the submenu. This brings up the simple menu to set the voltage range which will be retained in further processing.

    Note that the voltage range used should also be noted, i.e. whether the read-out values make poor or good use of the available dynamic range. Poor use of the dynamic range in the data may account for a high noise.
     

  3. Correction -> Non-Linearity:

    4. Press the menu button "Correction" (submenu "Non-Linearity"). The raw data in the ERD file which is displayed will be corrected for the non-linearity of the detector response using special calibration files. The plots are updated to show the corrected data. The correction is applied only the first time this correction is selected for a given set of data. The algorithm that is applied is identical to the PHT pipeline non-linearity algorithm and uses the same CAL-G files.
     
  4. Correction -> Read-Out Deglitching:

    5. First let's try to deglitch by using the standard parameters: Now let's try to modify the deglitching parameters to optimize the deglitching.

FIGURE 5: Ramp Deglitching Example: The original read-outs are marked with diamonds and connected with a dotted line, the deglitched read-outs are marked with squares. There are two glitches, one at time 45.7 and one at 46.2 [sec]. The first and last read-outs are marked with crosses and discarded.

  1. Correction -> Two-threshold deglitching:

    2. Using a different algorithm for deglitching but using the same philosophy for testing parameters, storing and displaying statistics, etc. The algorithm is described in chapter 5.1, section "Two threshold glitch recognition".
     
  2. View the Performed Operations:

    3. You may wish to take a look at what operations have been performed on a given measurement; these are written into the header. To view the header press the "View" button at the bottom of the window and choose "Header". In the middle of the header you will find rows beginning with "pr", which contain the information about deglitching etc. You can view the header for any level of reduction of the data; the relevant header lines concerning processing by PIA begin with "pr_" for ERD level, "prs" for SRD level and "prc" for SCP level.

  3. Save and Reload Intermediate Results:

    4. If you want to save your de-glitched and linearised ERD, press the menu button "Data" (choosing "Save"). "Data" is the button on the very left in the lower row. You can choose to save the data as a PIA Internal file or as a PIA FITS file. (Note that PIA FITS files are not exactly like the corresponding pipeline FITS files). Assuming you choose to store it as a PIA internal ERD file, you will create (by default) a file "P10401301401.IERD" in the directory PIA_SAVEDIR which was set up in the envi/logdef file. (The name corresponds to P1mm01301401.IERD with mm = measurement - 1, so this file corresponds to measurement 5). You can choose alternatively a different filename.
    While working on a reduction level dedicated window (in this case the ERD level) the data are corrected for the different effects on a temporary data structure, which can be used for further reduction, as explained below. The data in the internal buffer, however, remain unchanged. If you want to keep in the buffer corrected data on a certain level you should choose the option Save -> to ERD (SRD, SCP, ...) buffer, overwriting the uncorrected measurement or creating a new position in the internal buffer.

    (To reload the internal saved results follow the same procedures you used to read in the pipeline fits file you started with, except that you should select files from the category "Internal Save File". You should eventually arrive in the ERD window as before, but with deglitching already performed.)

    Finally:

  4. Process the data to Determine the Signal per Ramp:

    5. Press the menu button "Process Meas." choosing (for staring, P32 and any PHT-S measurements) "Fit Ramps, 1st order Pol." A new window will appear, the "PIA SRD Window", which has a design similar to the ERD-window. Two of the further options are fitting a 2nd or a 3rd order polynomial, both not recommended and only for test purposes. Another option for staring measurements is to use subdivided ramps. In this case the linear fits are performed to parts of the ramps, increasing the time resolution. This is of advantage for measurements with very long (and normally in this case, few) ramps.

    From PIA V8.0 on, the default for chopped measurements (except for P32, which is a special case, and PHT-S observations), is to use the so-called "Ramps Pattern" procedure, as explained in the former section, under Description of the data reduction steps. However, chopped measurements can be reduced using the same procedure as staring measurements.

Reduction of the SRD (to SCP)

The Signal per Ramp Data (SRD, in V/s) are examined, corrected for artifacts and averaged to become Signal per Chopper Plateau (SCP, also in V/s) data.

The SRD Window as shown in Figure 6 has a structure very similar to the ERD Window described in the previous chapter. Note that Figure 6 is for a C200 measurement and is therefore not exactly similar to the SRD Window which would follow from the processing of the P3 data shown in ERD Window in Figure 4.

Again there are 4 graphical windows, now containing the calculated signals in [V/s] with derived error bars. All general display features are as described in the previous chapter. Only the steps under the menus Selection, Correction, View and Processing are different, as they now refer to proceses performed on the SRD data type.

FCS measurements and astronomical data measurements are processed the same way at this level. 

FIGURE 6: The SRD Data Display for a C200 measurement. Note the array pixel indicators in the upper right corner. You may also notice that there are some glitches present which were not removed by deglitching on the read-out level. They are marked with crosses because they have subsequently been de-glitched at the signal level as described below. You can also see the effect of detector drift.

Now let's reduce the SRD, concentrating, as before, only on the most important steps:

Reduction of SCP Data (to SPD)

The average Signal per Chopper Plateau (SCP) data are further processed, e.g. by subtracting background and performing the power calibration to go from [V/s] to [W]. The resulting level is the so-called Standard Processed Data (SPD) level, which is the intermediate level of reduced data produced by the pipeline software.

The SCP Window, shown in Figure 8, has the same general structure as the other data reduction windows and offers the same display facilities. This example is again taken from a single-detector, chopped (P3) measurement, processed with the non-default modus (alternative to the default "Pattern procedure").

For the first time at the SCP level, we now have to distinguish between two cases for which different reduction steps are required:

In addition, there is a new feature:


FIGURE 8: The PIA SCP Data Display 


Let us consider Figure 8 in more detail:
  1. The first plot (on the very left) shows the average signal per chopper plateau. Note that the two signal levels corresponding to the source and the background are clearly distinguishable.
  2. The second plot shows medians and quartiles (in a PIA session using color, this plot appears clearer.)
  3. The third plot shows the chopper positions: The first and the third chopper positions are -60 and +60 degree off the center, while the second and the fourth chopper positions are on the center. Each chopper position appears four times.
  4. The plot on the very right shows the average detector temperature per chopper plateau; it is quite constant.
Now let's look at the "Array" display options, then let's reduce FCS data and, finally, reduce astronomical data.

1. Array Detector Data

Note that the array facilities are helpful for FCS measurements as well as for astronomical data made with an array.

C100 and C200 Data:

    In the case of the PHT-C array detectors a "lego" plot of the array [V/s] versus pixel will be shown. This can be helpful, e.g. to get an impression of the flatfield of the current measurements. Note that the variation in responsivity of the pixels often dominates this image. An example is shown in Figure 9. Note that for a raster map the lego plot is only given for one raster point; to obtain a map you have to apply the mapping tool which will be explained later.

    The lego plot can be modified (rotated or tilted) via the push-buttons. For a detailed description please refer to the section 3.4.3. on the PIA_XSurface Window.

FIGURE 9: Array Plot of C100 (showing flatfield properties) 

PHT-S Data:
      For PHT-S data a spectrum can be displayed as shown in Fig. 12 in a (2-dimensional) PIA_Xplot window for the first time. This can be done for each chopper plateau.
       

FIGURE 10: A PHT-S Spectrum on the SCP level

2. Processing Fine Calibration Source Data (FCS)

The detector responsivity varies by up to a factor of 2 or 3 on a time scale of hours to minutes. The actual responsivity at the time of the observation can be determined by an FCS measurement. The FCS has a known temperature and optical power output for a given heating power applied to it.

This processing step calculates the responsivity of the detector pixels at the time the measurement was taken and displays it.

Note: FCS measurements are neither possible at the moment nor planned for the PHT-S data!

Now let's reduce the FCS measurement:

  1. Straylight Subtraction:

    2. This is an optional correction. The FCS measurement may be contaminated by straylight from a bright source. Its contribution to the FCS flux is roughly estimated to be about 4%. However, this is a very crude estimation and should only be used in order to see how much influence straylight can have on the responsivity calculation.

    If you want to correct for this straylight contribution, press the menu button "Correction", submenu "Straylight correction". Select an on-source measurement (already reduced up to the SCP level) from which the straylight can be estimated and perform the correction.
     

  2. Calculate the Responsivity (actual):

    3. Press the menu button "Process" and choose "Responsivity Calculation". The default and the computed actual responsivities will be displayed in a new window as shown in Figure 11.

    Notice how large the differences between the actual and default responsivities can be! Click on "Accept as actual responses" to choose one of the options (average or median for FCS1 or FCS2 in the example) as the actual responsivity. Note that you will still be able to use the default values later in the calibration if you choose. Since the final flux is directly proportional to the responsivity, it is useful to print the responsivities and to mark the one used. With this step the reduction of FCS calibration measurements is finished.

    Basically, we have now "loaded" the actual responsivity into the PIA programme.
    Note: To continue the reduction after a new start of PIA, you have to reload a saved SCP file for the FCS measurement and calculate the actual responsivity again in order to load it into PIA.
     

  3. Save and Reload Intermediate Results:

    4. These options are discussed in the section on reducing ERD. Note that saving and reloading the SCP for the FCS measurement and then recalculating the responsivities is the only way to restore the responsivities for later use.

3. Processing Astronomical Data

We will reduce the Astronomical SCP data to subtract background and calibrate the signals (V/s) to in-band powers (W). Among the many possible actions we concentrate only on the most important ones:
  1. Vignetting:

    2. Press the menu button "Correction", submenu "Vignetting". This performs a correction for telescope vignetting according to data stored in a calibration file. This correction is optional -- it is important for measurements with large chopper throws, eg. P32 observations. Chopped measurements processed in the "pattern mode" do contain already the correction within their calibration, thus it should not be performed.
  1. Background Subtraction:

    2. This step is optional and can only be used if either an internal (i.e. chopped) or a separate external background measurement (also reduced to the SCP level) is available.

    To subtract a background press the menu button "Process" and choose "Background Subtraction". PIA provides two alternatives:
     

FIGURE 12: PIA Background Subtraction Window 

FIGURE 13: The SPD Window (corresponding to a P3 measurement)

Reduction of the SPD (to AAP)

The SPD level is further processed to the AAP level (Astrophysical Application, a level which is closely related to the pipeline product called Auto Analysis Results). The required operations are AOT-dependant. Generally, the flux calibration is performed. If there is a separate background measurement this can be subtracted from the source measurement.

The AAP Window is shown in Figure 14. It offers the same principal display options as the other windows described in the previous sections.

FIGURE 14: The AAP Window (corresponding to a C100 measurement)

    Differences between the Pipeline and PIA Files

    The file names and contents for PIA SPD files is different from that for Pipeline SPD files and the same applies to the AAP.

    Note for PHT-S

    Due to the structure of the pipeline files for PHT-S, the data and the reduction must be split into short (SS) and long (SL) wavelength parts, each part of the data having 64 pixels. It is not possible to treat both parts together, except for plotting them together by using "overplot/synchronised".

    In order to work on PHT-S data one has to load the desired part (SS or SL) explicitly via the menu "Data" (Submenu "Load")!

    Correction / Processing Steps

    Since the SPD level is not used anymore by normal PIA processing, and most of the correction and processing steps are common to the SPD and AAP GUI we describe them in one shot.
    The following steps have to / can be performed:
     
    1. Background Subtraction (SPD or AAP) [under Process button]:

      2. For data reduced in PIA from the ERD stage, internal background subtraction can be performed at the SCP, SPD  or AAP levels, while the external background subtraction should be better performed on one of the two last ones (because of possible different responsivities involved). For un-subtracted pipeline SPD files, background subtraction (either internal or external) must be performed here or at the AAP level.
      To enter subtraction of background, press the menu button "Process" (submenu "Background Subtraction"). For details see the discussion under SCP reduction. Note that for chopped measurements, where the responsivity is the same for source and background, it is better to subtract the background at the SCP level.
    2. Flux Calibration (only SPD level)[under Process button]:

      3. The in-band power is now converted into astronomically meaningful units of Jy or MJy/sr using special calibration files. Press the menu button "Process" (submenu "Extract Flux Density").
    3. Assign Astronomical Coordinates (SPD or AAP)[under Correction button]:

      4. This step, necessary for maps, can be performed individually to produce a tentative plot of the coordinates in the data display of the SPD or AAP window. It is also automatically included by the Flux Calibration step. (It reads the Coordinates from the IRPH files. The pointing files are discussed in the ISO IDUM).
      Note that for PIA to find the astronomical coordinates, the actual FITS directory at the time of assigning the coordinates must contain the proper IRPH files.
    4. Flat Fielding (AAP - C100/C200 detector data)[under Correction button]:

      5. Two methods are offered here for flat-fielding the array data:
      • Median filtering + background Flat Fielding, as described extensively in section 3.6.2.
      • Normalizing with 1st Quartile: a very simple flat-fielding method, based on a computation of the 1st Quartiles of  all the individual detector pixels (as representative for their background measurement) and a corresponding normalization. Specially suited for mini-maps, since the other, more sophisticated flat-fielding methods, cannot be applied in this case.


      NOTE: after applying a flat fielding correction the data MUST be saved into the internal buffer (or into a file which should be read in later) in order that the correction is contained in the buffer measurement when reading it for map obtention.
      Please note that both flat fielding methods described here can be applied also at the time of producing the map. In this case it is only affecting the map and not the data structure like in the AAP case.

    Basically,the data are now reduced and can be saved as files (Menu button "Data", submenu "Save"). For presentation (and further analysis) PIA provides some more features, mentioned in the following chapter.


Astrophysical Applications

This tool helps to combine/display results for presentation. It includes making maps, producing curves of growth, putting together spectra, etc.

This chapter gives just a short introduction to what applications are possible and how they can be started. For details the reader is referred to chapter 3.5. Astrophysical Applications Window.

The tool requires the measurements to be available in the AAP buffer, either coming from processing of lower levels or from reading the data from files.

The tool is entered from the PIA Top Window via the menu button "Buffers", submenu "Astrophysical Work". It brings up the Astrophysical Application Window with the following options:

  1. Multi-Filter Photometry for point sources
  2. Multi-Filter Photometry for extended sources
  3. Multi-Aperture Photometry for point sources
  4. Multi-Aperture Photometry for extended sources
  5. Spectro-Photometry
  6. Mapping
  7. Polarimetry for point sources
  8. Polarimetry for extended sources
  9. Show/Correlate Mean Values
  10. Summary/Print Values
Applications using several measurements as input:

For all Astrophysical Applications options, except for Spectro-Photometry and Mapping (on which the further reduction is performed on a per measurement basis), several measurements are chosen to be combined. The desired measurements will be selected using the measurement selection window you are already familiar with, like for plotting and reducing data at the various stages of reduction.

From every measurement several variables are calculated which yield a value per variable per measurement.
The main calculated variables are flux and surface brightness per measurement, accompanied by filter, aperture, polarizer, etc. In the case of a C100 / C200 measurement, fluxes are obtained by integrating over the full array, and surface brightnesses are obtained by averaging over the array.
In the case of C100 or C200 measurements a choice of detector pixels to be used is given. The selected pixels are then used to obtain full fluxes and brightnesses from the array. Please note that at first at this stage a PSF correction is applied by data from these detectors.

Additionaly, the possibility of colour corrections is offered by a menu with two source spectrum alternatives: black-body spectrum (with a choice of temperature of the BB) and power-law spectrum (with a choice of its index). If one of the colour corrections is chosen, the calculated factors from folding source spectrum and filter curve correct the data. The factors used are presented to the user in a text window.
 

Note: in case an AAP level measurement contains several chopper plateaux and/or raster positions (eg. a mapping observation, a chopped source vs background observation which has not been background-subtracted, etc.), the average of all elements corresponding to a variable is taken, which is in most cases not meaningful.

    Multi-Filter Photometry (for point or extended sources)

    The aim is a 2-dimensional plot displaying flux density (point source choice) or surface brightness (extended source) versus central wavelengths of the filters used. The input consists of several measurements at various wavelengths combined as described above. Then the desired plot will be displayed. An example is shown in Figure 15. At the same time a text display/print window pops up, giving the results in table form.

    FIGURE 15: Example for the Multi-Filter Photometry 

    Multi-Aperture Photometry (for point or extended sources)

    This works the same way as the tool for multi-filter photometry, but generates a curve of growth (flux vs. aperture instead of wavelength).

    Polarimetry (for point or extended sources)

    This works the same way as multi-filter photometry, but plots the flux density against the three angles of the polarizer instead of the wavelength.

    Show/Correlate Mean Values

    By this option the values per variable per measurement, obtained as described above, are then accessible all at the same time for comparisons, plotting, etc. via a special PIA feature (the PIA Show_Structures Menu).

    Summary / Print Values

    This option creates text files, containing the most relevant values from the AAP level, in the form of tables. The text files can be saved and printed.
Applications using single measurement as input:

    Spectro-Photometry

    This opens a tool for fitting spectral lines and continuum. It works on one AAP level measurement.

    Mapping

    This opens a tool to create maps for raster and dedicated mapping AOTs (e.g. sparse maps PHT17/18/19 and PHT37/38/39, PHT32, or raster observations with P03, P22 and P40).

    The basic steps are:

    1. Select a measurement
    2. Define the Map Parameters
    3. Produce Map using spacecraft pointing information. This is the pointing as measured and stored into the IRPH file or
    4. Produce Map Ignoring Actual Pointing

      5.  This yields an approximated map under the assumption that the spacecraft raster points build a perfectly regular grid.
    5. Print Map
    6. Save Map
       
       
      Chapter History:
          Date  Authors  Description 
      04/07/1995  Ingolf Heinrichsen (MPIK)/Wai MingTai (DIAS)  First Version 
      08/05/1996  Martin Haas (MPIA)/Carlos Gabriel (ESA)  General Update 
      17/03/1997 Carlos Gabriel (ESA-SAI) Update
      21/04/1997 Carlos Gabriel (ESA-SAI) Update
      04/06/1997 Carlos Gabriel (ESA-SAI) Update (V6.3)
      13/02/1998 Carlos Gabriel (ESA-SAI) Update (V7.0)
      18/08/1999 Carlos Gabriel (ESA-SAI) Update (V8.0)
      17/03/2000 Carlos Gabriel (ESA-SAI) Update (V8.2)