ISOCAM Interactive Analysis User's Manual Version 5.0 - ISO - ESA

234 CHAPTER 20. ADVANCED DATA CALIBRATION
3. method=‘tcor’
method: Deglitch tcor. This method attempts to attempts to avoid the problems that
arise from instability by initially transforming the cube into a zero-mean cube and
then deglitching. The algorithm is:
(a) Compute the zero-mean, D, of the input .CUBE, cube in:
D = √ 2
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cube in(∗, ∗,i) − √ 1
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cube in(∗, ∗,i− 1) + cube in(∗, ∗,i+1))
(b) Compute S t, theNsigma clipping of D
(c) For each IMAGE of cube in:
i. Compute I, whereI = IMAGE − median(IMAGE,5)
ii. Compute S p, theNsigma clipping of I
iii. A glitch has occurred if abs(D(∗, ∗,f)) >S t and abs(I) >S p
iv. Replace glitched pixels cube out(i, j, k) bycube out(i, j, k − 1)
Some criticisms of the tcor have been made – under certain conditions it will eradicate
your data. As with all deglitching techniques it should be used with care.
routine called: deglitch tcor
PDS side effects: Glitches removed from IMAGEs in .CUBE, i.e. .CUBE is modified.
Glitched pixels also flagged in .MASK.
reference: online help.
4. method=‘mm’
method: Deglitch MM (Multiresolution Median Transform). The Multiresolution Median
Transform works on the principle that in temporal space glitches are small scale
structures and source signal will always be large scale structure. Consequently, this
method may fail for glitches of very long duration. In general though, it is very
robust and handles non-stabilized data well. It is especially good for observations
where many IMAGEs are accrued. This method is the default.
routine called: mr1d deglitch
PDS side effects: Glitches removed from IMAGEs in .CUBE, i.e. .CUBE is modified.
Glitched pixels also flagged in .MASK.
reference: ISOCAM Handbook, Chapter Data processing methods, Section Deglitching
using the Multiresolution Median Transform (MMT).
5. method=‘sky’
method: sky cube deglitching. Faders and dippers can be rejected from rasters with
redundant observation. Flags .MASK of a PDS. The input data (cube and image)
should be flat-fielded. The algorithm is:
(a) The mosaic is created and back-projected into the image again.
(b) The image is rebinned into a cube
(c) Standard deglitching is performed on the difference between the original and the
back-projected cube.
routine called: deglitch sky
PDS side effects: Glitched pixels are flagged in .MASK. A new .RASTER is created.