5.  PIA P32 TOOLS - Deglitcher

 

Figure 1: Window for Deglitcher with default settings.

 

The 'Deglitcher' window is dominated by the data display, framed on the right hand side by display options and access to manual de-/selection, and on the bottom by the parameter interface for the deglitcher routine itself.

 

5.1    Display

The data points shown in the display are the pairwise differences of subsequent readouts of the pixel selected. A brief listing of different colors and symbols is given below.

red square
valid data point
blue square
data point taken during spacecraft slews
green square
patched data point
yellow cross
invalid data point
blue cross
invalid data point taken during spacecraft slews
dotted vertical line
borderline between chopper sweeps

 

5.2    Display/Window Options

The right panel of buttons on the deglitcher window controls the display and selection of data.

 

5.2.1 Navigate

These buttons are always active and enable the user to navigate through the dataset. The original display can be restored by hitting the 'Free' button in the 'Scaling' section.

Up
Moves the view box 1/3 of the total display area upwards, i.e. the data appears to move downwards.
Left
Moves the view box 1/3 of the total display area to the left, i.e. the data appears to move to the right.
Right
Moves the view box 1/3 of the total display area to the right, i.e. the data appears to move to the left.
Down
Moves the view box 1/3 of the total display area downwards, i.e. the data appears to move upwards.
Zoom In
Magnifies the rectangular area marked/opened with the left mouse button and sets the scaling to 'fix'. More than one data point needs to be selected for a reasonable result.
Zoom Out     
Compresses the data set along the time-(x-)axis by 50%.

 

5.2.2 Scaling

This panel controls the magnification/scaling of the data on the display.

Free
Scales the data set to fully cover the display.
Fix
Fixes the scaling in case of 'Zoom In'.

 

5.2.3 Display

With this panel the display can be customized, i.e. selection of data type, plot symbols and errorbars.

All    (default option)
Displays all data points.
Valid Only
Shows only valid data points.
Dots
Data points are displayed as dots.
Symbols
Data points are displayed with squares.
No Errorbars
Errorbars are not plotted.
Errorbars
Errorbars are plotted for each data point.

 

5.2.4 Manual deglitching

Data points are marked with the mouse. Opening a rectangle from the lower left corner to the upper right corner while holding the left mouse key down selects the area around the desired data points, after having pressed one of the following buttons.

Select
The data points within the marked area are flagged to be valid data points.
Deselect
The data points within the marked area are flagged to be invalid data points.
 

5.2.5 Quit/Exit

The deglitcher window cannot be active simultaneously with other windows of the P32 package. It has to be closed if one wants to proceed with P32 Tools.

Quit
Closes the window, discarding all changes.
Exit
Closes the window, accepting all modifications.

 

5.3 Deglitching

Deglitching of the data is essential, especially in maps with overall low flux and extended structures. In the initial map making process, the data is run through a so called 'spike detector' that identifies potential glitches. This deglitcher interface allows more sophisticated glitch removal, based on the initial results of the spike detector.

Figure 6: Work principles of the deglitcher.

 

The basic functionality is illustrated in Figure 6. The lower part shows the data and the result from the deglitcher, the upper part schematically shows thresholds, spikes and glitch tails. The parameters of the deglitching routine are described below.

Fraction bad readouts
Controls the maximum amount of data that can be flagged bad because of deglitches.
Time const. spike tails Varies the time constant for the glitch tail. It determines how many seconds after the glitch detection the data are still affected.
Spike inclusion Threshold Controls which events are marked as spikes. Glitch candidates above this threshold are considered further.
Spike clipping Threshold This parameter determines at what signal level after the spike the signal is considered back to normal. I.e. when the value of the data points after the spike is supposed to match more or less the average value at that time/position within the measurement.
Patch In the process of deglitching, a lot of data points can be deselected leaving significant gaps in the data set. Part of these possible gaps can be patched with data points from other chopper sweeps of the same sky position. The patching is necessary to ensure a continuous illumination history as basis for the drift fitting. After activating 'Patch', the 'deglitch' button needs to be pressed again. The patched data points will be shown as green squares.

 


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