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

294 CHAPTER 22. SECOND ORDER CORRECTIONS
80
60
N
40
20
0
-0.3 -0.2 -0.1 0.0 0.1 0.2
jitter offset (arcseconds)
Figure 22.1: Distribution of jitter offsets as computed with the gauss method. Data are from a
CAM calibration observation of HIC 73005 (also featured in Chapter 4). In this particular case
the jitter standard deviation is observed to be about 0.065 ′′ .
The routine corr jitter is the user interface to the jitter computation routines. It can
operate on any flavor of PDS. It is recommended that the PDS is at least dark corrected and
deglitched before attempting to compute the jitter. To perform the default jitter computation,
corr jitter can be run as:
CIA> corr_jitter, pds
You can view the computed jitter offsets with:
CIA> plot, pds.du
CIA> plot, pds.dv
However, jitter computation is an interactive process and a choice of methods and options
are available. The available jitter computation methods are described below. See Figure 22.2
for a comparison of jitter computation methods.
1. method=‘gauss’
method: Apply a 2D elliptical gaussian fit to each IMAGE. See the on-line help for
fit 2dgauss for a description of the gaussian function.
routine called: fit 2dgauss
PDS side effects: .DU and .DV are filled with the jitter offsets du, dv for each image.
2. method=‘psf’
method: Select the best fitting theoretical PSF from a library.
routine called: fit psfstruc
PDS side effects: .DU and .DV are filled with the jitter offsets du, dv for each image.
Some useful keyword options are: