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3.8 Signal deglitching

synopsis:  (1) reduction of statistical uncertainty by removing outliers, (2) increase of statistical uncertainty due to decrease of effective integration time.

limitations and applicability:
For measurements with less than 22 signals per chopper plateau or per raster point the iterative method is not used, instead all signals with ${\Delta}s\,>~1\,$V/s are removed.

description:
The distribution of a number of consecutive signals (=local distribution) is analyzed and outliers are removed according to a kappa-sigma criterion. This is repeated several times.

purpose correction:
Removal of signal glitches/outliers that are not recognized during ramp deglitching (Sect. 3.4).

uncertainty/noise introduced:
None, reduces the statistical uncertainty.

auxillary data:
see Table 2

Table 2: Default parameters for signal deglitching
Parameter  Value  Description
min_deglitch 5 minimum points to apply
max_error 1 V/s maximum error allowed if number of
    points is less than min_deglitch
n_iter 2 number of iterations of deglitch filter
n_local 20 number of points in local distribution
n_step 1 the number of points to move the `box'
    for the local distribution each time
n_sigma 3 Rejection factor: number of standard
    deviations from local median.
n_bad 2 number of times point has to be flagged
    as `bad' before it is rejected.

Keyword(s):
MINDEG: Min points for deglitcher SPD header
MAXERR: Max error if points < MINDEG SPD header
NITERATE: No. of iterations of deglitcher SPD header
NLOCAL: No. of local points used by deglitcher SPD header
NSTEP: Deglitcher step size SPD header
NSIGMA: amount rms from local median SPD header
NBAD: badness count limit SPD header
P??NSIG : number of valid signals on plateau (??=P1,P2,P3,C1,C2) (SPD record)


next up previous contents
Next: 3.9 Discarding signals in Up: 3. Derive SPD level Previous: 3.7 Dark signal subtraction
ISOPHOT Error Budgets: Derive_SPD Processing Steps, Version 1.0, SAI/98-091/Dc