3.   PIA P32 Tools - Map DISPLAY Options

 

Figure 1: Window for Map Display Options with default settings.

 

This window controls the display of the P32 maps within P32tools. Here the map units as well as the photometric calibration method can be selected. Furthermore the contribution of slew data as well as the contribution of each individual detector pixel to the displayed map is defined here.

 

3.1    Calibration

The data is prepared for display in agreement with ISOPHOT photometric calibration and PIA correction algorithms. The corrections are only applied to display the data and are lost once the data is exported from P32Tools and back to PIA. There, the standard PIA processing from SCP onwards has to be applied.

 

3.1.1 Signal Linearization

'Linearize Signal' has be switched on to be consistent with the general ISOPHOT calibration scheme.

 

3.1.2 Map Units

The user can select on of the following units for the map display:

A map with surface brightness units might be most appropriate when dealing with extended emission, point source units in case of point sources and signal units for working on basic signal level.
When using point source units, the peak flux of a point source (in Jy/beam) must be divided by the correction factor for the point spread function fpsf in order to obtain the point source flux (in Jy). This factor is given for a detector pixel and depends on the filter (see ISOPHOT handbook).

 

3.1.3 Use of FCS Measurements

For the actual calibration of the map, either the actual responsivity as determined from the corresponding FCS measurements or the default responsivity can be used. The exact flux calibration options are:

Default
The default responsivity will be used.
Avg. FCS's   (default option)
The average of actual responsivities as determined from the corrsponding two FSC measurements will be used.
FCS#1
Only the actual responsivity of the first FCS measurement will be used.
FCS#2
Only the actual responsivity of second FCS measurement will be used.

The default flux calibration option is to use the average of both FCS measurements . Only one FCS measurement should be used in case the other one clearly has problems due to strong glitches or drift. The default responsivity should only be used when the signal level of FCS illumination does not match the average signal in the map.(Typically, the average map signal and FCS signals should be within a factor of 3 of each other.)

 

3.2    Data Selection (Slew data handling)

The data acquisition was independent from the spacecraft (raster) movement. Data is taken continuously even during slews between raster points. For the map making the two options for the use of slew data are:

The pointing information for the data taken during the slewing between raster points is less accurate. The signal-to-noise for slew data is a lot lower than for data taken at raster points. By default the slew data is not used for the map making, which is the recommended option.

 

3.3    Select detector pixels to be displayed

The two detectors available for P32 measurements, have either 4 pixels (C200) or 9 pixels (C100). Each of these pixels is treated as an independent detector performing an independent measurement. The pixel options for C100/C200 are:

Select all
(Re)Selects all detector pixels for map making.
Deselect all
Deselects all pixels for map making.

Default pixel selections for map making are:

C100
All detector pixels selected (#1 - #9)
C200 All detector pixels selected (#1 - #4)

By default, all detector pixels are selected for the map making.
To facilitate the pixel selection, use all of them invoking 'Select all' or clear this or any selection with 'Deselect all'. Individual pixels can be de/selected at all times using the numbered single pixel buttons.

 

3.4    Apply Flatfielding algorithm

The C100 and C200 detector pixels are calibrated separately. Although each detector pixel has the best possible photometric calibration, inconsistencies of a few percent in the photometric calibration among detector pixels cannot be excluded. The inconsistencies are due to (1) the assumption that each detector pixel covers the same solid angle on the sky, and (2) the signal uncertainties in the FCS measurement.

The inconsistencies cause the typical checkerboard or stripe pattern in the map. In order to remove such pattern a flatfielding algorithm has been implemented which normalises the calibrated signals of the selected detector pixels to the average of the lower 25 percentiles (i.e. lower quartiles) of the sky brightness measured by these pixels. It is assumed that each selected detector pixel has seen a large fraction of the same sky area and that the inconsistencies can be removed by scaling of the signals.

Consequently, the correction gives better results for larger maps where the overlap area is larger.

Application of this correction can be selected (default option) or de-selected.

 

3.5    Exiting ...     (Bottom line)

Close
Closes the window accepting all the options checked.
Cancel
Closes the window discarding all the changes made to the initial configuration.
Help
Displays the help file for this window.

 


Other P32Tools helppages:
  1. Data Initialization Options
  2. Main Window
  3. Map Display Options
  1. Inspect Single Pixel
  2. Deglitcher

PHT32 Tools Help text      written by S. B. Peschke          July 2001