3.7) The PIA Mapping Simulation System

The system can be used for testing the following:

The system is divided into three main stages:

sky simulation : a portion of the sky as well as the user defined number of sources with their respective positions in the sky, fluxes / brightness and sizes (circular and bar structures are included ) are defined.  The choice between a flat or a gradient background is also available.  Convolution with the footprint of a selected filter yields an image of the convolved sky in addition to the pure sky.  These images together with the parameter set used to create them are the products of this portion of the simulation, which can be saved as data entities for reuse at any time.

observing mode specification : the observing mode is defined together with the raster parameters (number of raster legs and points per leg, distance between legs and points, central position of the raster).  Both the orientation of raster vs sky as well as the orientation of spacecraft vs sky are necessary for establishing the exact positioning of the detectors (and hence the "measured" flux) on the sky at any step of the observation.  The result is an AAP level data structure which can be used within the PIA environment as any real observation, e.g. deriving the corresponding image.

instrumental effects : the expansion of every spatially "measured" point into a time series of signals as would have been recorded by a real observation is done together with the inclusion of instrumental effects, like the transient behavior of the ISOPHOT detectors, the disturbances produced by cosmic rays, different detector pixel response and a random noise contribution.  The product, a SRD data structure, can also be ingested into PIA for virtually simulating the data analysis.

The PIA mapping simulation system includes a widget based graphical user interface, with dedicated menus for each of the three parts of the system, as mentioned above.  Visualization of the created sky images with superimposed raster and detector pixel positions is also accessible from the main menu.  The visualization tools attached to this GUI are common to the PIA mapping system, thus offering the user the main IDL capabilities with respect to image display and manipulation from comprehensive menus.

3.7.1) The PIA Map Simulation Window

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FIGURE 1: The PIA Map Simulation Window

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Parameters

This pull-down item offers the following options:

Edit/change sky map parameters

This brings up the PIA Map Simulation Parameters window shown in Figure 2.

Edit/change data parameters

This brings up the PIA Raster Simulation Parameters window shown in Figure 6.

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Sky Simulation

This pull-down item offers the following options:

Using parameter table

This will run the sky simulation using the parameters specified with the PIA Map Simulation Parameters window.

Using graphic derivation

This starts the graphic derivation of the sky simulation using the IDL prompt.  With this option, the user is asked to specify the necessary parameters at the IDL prompt by answering series of questions.  As the inputs are made, the program shows displays and information to guide the user along.  Hence, you are encouraged to try this graphic version to familiarize yourself with the sky simulation system.

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Data Simulation

This pull-down item offers the following options:

Using parameter table

This will run the data simulation using the parameters specified with the PIA Raster Simulation Parameters window.

Using graphic derivation

This starts the graphic derivation of the data simulation whose end products are AAP and SRD data structures.  With this option, the user is asked to specify the necessary parameters at the IDL prompt by answering series of questions.  As the inputs are made, the program shows displays and information to guide the user along.  Hence, you are encouraged to try this graphic version to familiarize yourself with the raster (AAP data) simulation system.

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Display

This pull-down item offers the following options:

Convolved Sky Image (Jy/beam)

This shows the simulated sky convolved with the footprint of the selected filter in units of Jy/beam.  For example, see the Figure 4.

Convolved Sky Image (MJy/sr)

This shows the simulated sky convolved with the footprint of the selected filter in units of MJy/sr.  This is exactly the same as the previous image except for the units (MJy/sr instead of Jy/beam).

Pure Sky Image

This shows the simulated sky (ideal image) in arbitrary units, see Figure 3.  Please note that the scale is meaningless in this image.

Image + Measured Positions

This shows the simulated sky convolved with the footprint of the selected filter in units of Jy/beam plus the user defined raster positions.  For example, see the Figure 8.

 ... + Det.Pixel pos. (in S/C coord) (Jy/beam)

This shows the simulated sky convolved with the footprint of the selected filter in units of Jy/beam plus the user defined raster positions in the spacecraft coordinates instead of sky coordinates.  For example, it looks like Figure 9 (except that the unit is in Jy/beam).

 ... + Det.Pixel pos. (in S/C coord) (MJy/sr)

This shows the simulated sky convolved with the footprint of the selected filter in units of MJy/sr plus the user defined raster positions in the spacecraft coordinates instead of sky coordinates.  For example, see the Figure 9.

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Load map

This calls the Please Select a File window as shown below.

Please specify the name of the file containing the saved simulated map and its directory path.

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Data -> PIA

This pull-down item offers the following options:

AAP -> PIA

Select this option to load the generated AAP data into the PIA buffer.

SRD -> PIA

Select this option to load the generated SRD data into the PIA buffer.

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Save ...

This pull-down item offers the following options:

Generated map

This calls the Please Select a File for Writing window, which asks for a filename (and directory) under which the generated map will be saved (a default name is proposed).

Generated AAP

This calls the Please Select a File for Writing window, which asks for a filename (and directory) under which the generated AAP data will be saved (a default name is proposed) in internal PIA format.

Generated SRD

This calls the Please Select a File for Writing window, which asks for a filename (and directory) under which the generated SRD data will be saved (a default name is proposed) in internal PIA format.

The proposed default name has the following format: "C1" or "C2" depending on the detector used, followed by "99" to differentiate it from real observations, and the remaining digits represent the time the data was simulated (i.e., the each set of two digits is in the order of the month, date, hour and minute).  For example, "C19906171703" can be decoded as a simulated data (looking at the "99" following the "C1") using the C100 detector created on June 17 at 17:03 or 5:03 PM.

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QUIT

3.7.2) Sky Simulation

Using the PIA Map Simulation Parameters window

Selecting the "Edit/change sky map parameters" under the "Parameters" on the main window brings up the PIA Map Simulation Parameters window shown in Figure 2.  See the detail on each parameter below.

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FIGURE 2: The PIA Map Simulation Parameters window

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Skybin size S (arcsec) and Sky sidelength L (arcsec):  For now, the skybin size is fixed as 7.5 arcsec, but you can choose the size of the sky by specifying the side-length in arcsec.  The simulated sky is always square in shape.

Nr. of sources:  Enter the number of sources you would like to create, and then you must hit the Enter button to modify this window to accommodate that number of inputs.  You can create circular or bar structures, and you also have the option of entering either the flux or brightness for each.  Specify the position of each source, and enter their sizes (Z-dim = 0 for circular sources).  Don't forget to select the correct option, Jy or MJy/sr, for each Flux/Brightness value you enter.  For a point source, simply make the size small enough.

Flat Background [MJy/sr]:  Enter the brightness for a flat background.  If you don't want a flat background, change the default value of 10.00 MJy/sr to 0.00 MJy/sr.

Gradient Bckgr. [MJy/sr] and Grad. Bckgr. Positions:  Enter the brightness values at two different locations on the sky, and the gradient background will be interpolated between these values.  We suggest that you choose the diagonally opposing corners of the sky.

Convolution Filter:  Choose the number corresponding to the filter you would like to use.  For example, the number 5 represents the C100_100 micron filter.

Click the button, "Set Default parameters" to change back to default parameters or click on the "Quit" button to use the inputs you made on this window.

Running the sky simulation

If you would like to use the values specified on the parameters table, then simply click on the option, "Using parameter table" under the "Sky Simulation" button on the main window.  When the sky simulation is completed, you can view the results (i.e., the pure sky image and the convolved sky images) using the "Display" button.

If you would like to run the sky simulation graphically at the IDL prompt, simply click on the second option, "Using graphic derivation" under the "Sky Simulation" button and answer the proposed questions at the IDL prompt.  The results will be displayed as the necessary inputs are made, so you can follow the program graphically.

Viewing the sky simulation results

When the sky simulation is completed regardless of the method you used (using parameter table or using graphic derivation), the results are accessible from the main window using the "Display" button (only the first three options are available).  The Figure 3 shows an example of a simulated pure sky image, the Figure 4 the convolved sky image in Jy/beam, and the Figure 5 the surface plot of the convolved image.  This example case shows three different sources: a point source at the center of the sky, a extended circular source and a bar structure.  The available visualization tools are common to the PIA mapping system, thus offering the user the main IDL capabilities with respect to image display and manipulation from comprehensive menus.

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FIGURE 3:  The Pure Sky Image of three different sources

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FIGURE 4:  The Convolved Sky Image in Jy/beam.  The pure sky image in Figure 3 was convolved with C100_100 filter as shown in the plot title.

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FIGURE 5:  The surface plot of the Figure 4.  This is produced using the "Surface" button in Figure 4.

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Now you can save the generated map by selecting the "Generated map" under the "Save ..." button on the main window, which calls the Please Select a File for Writing window.  A default name is proposed.

3.7.3) Data Simulation

The steps involved in the data simulation are very similar to those involved in the sky simulation.  First, you must define the necessary parameters either using the PIA Raster Simulation Parameters window in Figure 6 or using the IDL prompt for graphic derivation.  Then, select the appropriate option under the "Data Simulation" button in the main window; choose the first option, "Using parameter table" if you defined the parameters using the PIA Raster Simulation Parameters window or choose the second option, "Using graphic derivation" if you would like to run the data simulation graphically by making inputs at the IDL prompt.  Finally, you can examine the results (the measured positions superimposed on the convolved sky image in the sky coordinates or the same in the spacecraft coordinates as shown in Figure 8 and Figure 9 respectively) using the "Display" button.  Also, you can load the generated AAP and SRD data into the PIA buffer or save it to a file.

Using the PIA Raster Simulation Parameters window

Selecting the "Edit/change data parameters" under the "Parameters" button on the main window brings up the PIA Raster Simulation Parameters window shown in Figure 6.  See the detail on each parameter below.

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FIGURE 6: The PIA Raster Simulation Parameters window

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Raster/AOT parameters

• Central pos. Y-Z [arcsec]:  Enter the central position of the raster.  The first box is for the horizontal coordinate and the second box for the vertical coordinate in the convolved sky image.  The default has the raster centered at the origin.
• Raster Points & Legs N-M (<33):  Specify the number of raster points and legs.  If you plan to simulate a P32 observation, you should consider its use of the chopper (i.e., don't make the number of points too large).  Although the limit is 32, real observations don't use a dimension quite so large.
• Distances dN - dM [arcsec]:  If you choose to do a P22 observation, specify the distance between the consecutive raster points and legs in arcsec.  This information is irrelevant if you are simulating a P32 observation.
• S/C Roll angle [degrees]:  Enter the angle of rotation for the spacecraft with respect to the sky in eastward direction from the north.  The detector orientation (i.e., the raster pattern in most cases) will be rotated through this angle in the counterclockwise direction from the north in the convolved sky image, except for the special P22 case as discussed below.  The rotation is pivoted at the center of the raster.  For example, a P32 observation of 3 x 9 raster with a roll angle of 30 degrees is shown in the Figure 8.
• P32 option (0=P22):  If you opt to do a P32 observation you need to choose the raster step size from the choices given in the Figure 7 which is displayed when you click on the "See list" button.  For a P22 observation, use the default value of 0.

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FIGURE 7:  The P32 raster step options display window

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• ORIEntation flag (ATTRORIE):  For the P22 observations, there are cases where the detector orientation (i.e., the spacecraft orientation) is not aligned with the raster pattern but rather rotated by some angle.  If you opt for this special case, then change the default value of 1 to 0 (default is for a simple P22 observation where the raster orientation is aligned with the spacecraft coordinates) and specify that desired angle in the next line (the raster pattern ROTA in degrees).  This value corresponds to that defined by ATTRORIE keyword in the header of a real observation data.  This is irrelevant when simulating a P32 observation.
• Raster pattern ROTA [degrees]:  If you choose to do a special P22 case in which the raster pattern is mis-aligned with the spacecraft coordinates and you changed the previous parameter, ORIE, to equal 0, then specify the angle of rotation for the raster pattern with respect to the sky coordinates.  An example of this special case is shown below where the ROTA is 40 degrees and Roll angle is 10 degrees (i.e., the spacecraft is rotated through 10 degrees and the raster pattern is rotated through 40 degree, both with respect to the sky coordinates).  Note that the display is in the spacecraft coordinates and that the positions represented by the numbers 1 - 9 are the pixel centers for the first raster point in this 5 x 7 observation.  Again, this is irrelevant when simulating a P32 observation.



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Data parameters

• SRD derivation:  Check this option if you would like to produce a SRD level data as well.
• Transients inclusion:  Check this option if you would like to simulate transients in the SRD data.  This option is only available when the SRD derivation button is checked.
• Glitches inclusion:  Check this option if you would like to simulate glitches in the SRD data.  This option is only available when the SRD derivation
  button is checked.
• Transient parameters E & p:  If you are familiar with the transient behavior ("offset exponential function") and would like to change the transient parameters you can do so by modifying these parameters.
• Pixel Resp. variation ("Unflatfield") [%]:  This refers to the "unflatfield" or the mean responsivity deviation per pixel.
• Noise level [%]:  Enter the noise level desired.
• Individual signal uncertainty [%]:  Define the individual signal uncertainty.  Since this SRD data is not derived from an ERD data, this needs to be specified to mimic a real data.
• Start parameter for random calculations (SEED): Within the simulations there are several random calculations for adding noise or glitches to the data. This parameter set the starting point for deriving random numbers (by default 0),  so that the user can force identical or different random numbers to be derived.

• If you are familiar with the timing parameters and would like to modify them, then click on the button, "Set own timing parameters" to call the following the Set Timing Parameters window.


 
• Click on the "Default parameters" button to revert back to the default values or click on the "Quit" button to use the inputs and modifications you have made.

Running the data simulation

If you would like to use the values specified on the parameter table, then simply click on the option, "Using parameter table" under the "Data Simulation" button on the main window.  When the simulation is completed, you can view the results (i.e., the convolved sky image plus the measured positions either in the sky coordinates or in the spacecraft coordinates) using the "Display" button.

If you would like to run the data simulation graphically at the IDL prompt, simply click on the second option, "Using graphic derivation" under the "Data Simulation" button and answer the proposed questions at the IDL prompt.  The results will be displayed as the necessary inputs are made, so you can follow the program graphically.

Viewing the data simulation results

When the data simulation is completed regardless of the method you used (using parameter table or using graphic derivation), the results are accessible from the main window using the "Display" button (the last three options become available).  The Figure 8 shows an example of the "Image + Measured Positions" option under the "Display" button.  This shows the convolved sky image plus a simulated P32 observation of 3x9 raster rotated through 30 degrees.  The white crosses show all the measured positions (i.e., including the chopper positions) and the raster points are represented with reddish crosses.

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FIGURE 8:  An example of "Image + Measured Positions" display.

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The Figure 9 shows an example of the "... + Det.Pixel pos. (in S/C coord) (MJy/sr)" option under the "Display" button.  Note that the "... + Det.Pixel pos. (in S/C coord) (Jy/beam)" is exactly the same as this one except for the unit, Jy/beam instead of MJy/sr.  The Figure 9 is basically the same as the Figure 8 except that it is in the spacecraft coordinates instead of the sky coordinates (hence, usually zoomed in).  Also, it shows the pixel centers at the first raster position with the numbers 1 - 9.

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FIGURE 9:  An example of "... + Det.Pixel pos. (in S/C coord) (MJy/sr)" display

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Now, you can save the generated AAP or SRD data to a file by using the "Generated AAP" or "Generated SRD" under the "Save ..." button on the main window.   This calls the Please Select a File for Writing window and proposes a default name.  You also have the choice to load it into the PIA buffer using the "AAP -> PIA" or "SRD -> PIA" under the "Data -> PIA" button, so that you can use it like any other real observation.  The Figure 10 shows a simulated AAP data in the PIA buffer, and the Figure 11 shows a simulated SRD data in the PIA buffer.

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FIGURE 10:  A simulated AAP data loaded into the PIA buffer

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FIGURE 11:  A simulated SRD data loaded into the PIA buffer

3.7.4) Instrumental Effects

FIGURE 12:  A simple P22 observation of 3 x 5 raster

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FIGURE 13:  The PIA display of the SRD data derived from the simulated P22 observation in the Figure 12

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FIGURE 14:  The zoomed image of the AAP data of a certain pixel.  This is from the observation shown in Figure 12.

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FIGURE 15:  The zoomed image of the SRD data of a certain pixel corresponding to the AAP data shown in the Figure 14.  This is from the observation shown in the Figure 12.