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Astronomical Data Analysis Software and Systems VII
ASP Conference Series, Vol. 145, 1998
R. Albrecht, R. N. Hook and H. A. Bushouse, e
Ö Copyright 1998 Astronomical Society of the Pacific. All rights reserved.
ds.
Data Analysis with ISOCAM Interactive Analysis System
--- Preparing for the Future
S. Ott 1 and R. Gastaud 2 , A. Abergel 3 , B. Altieri 1 , J­L. Augu‘eres 2 ,
H. Aussel 2 , J­P. Bernard 3 , A. Biviano 1,4 , J. Blommaert 1 , O. Boulade 2 ,
F. Boulanger 3 , C. Cesarsky 5 , D.A. Cesarsky 3 , V. Charmandaris 2 ,
A. Claret 2 , M. Delaney 1,6 , C. Delattre 2 , T. Deschamps 2 , F­X. D’esert 3 ,
P. Didelon 2 , D. Elbaz 2 , P. Gallais 3 , K. Ganga 7 , S. Guest 1,8 , G. Helou 7 ,
M. Kong 7 , F. Lacombe 9 , D. Landriu 2 , O. Laurent 2 , P. Lecoupanec 9 ,
J. Li 7 , L. Metcalfe 1 , K. Okumura 1 , M. P’erault 3 , A. Pollock 1 ,
D. Rouan 9 , J. Sam­Lone 2 , M. Sauvage 2 , R. Siebenmorgen 1 ,
J­L. Starck 2 , D. Tran 2 , D. Van Buren 7 , L. Vigroux 2 and F. Vivares 3
1 ISO Science Operations Centre, Astrophysics Division of ESA,
Villafranca del Castillo, Spain
2 CEA, DSM/DAPNIA, CE­Saclay, Gif­sur­Yvette, France
3 IAS, CNRS, University of Paris Sud, Orsay, France
4 Istituto TESRE, CNR, Bologna, Italy
5 CEA, DSM, CE­Saclay, Gif­sur­Yvette, France
6 UCD, Belfield, Dublin, Ireland
7 IPAC, JPL and Caltech, Pasadena, CA, USA
8 RAL, Chilton, Didcot, Oxon, England
9 DESPA, Observatoire de Paris, Meudon, France
Abstract.
This paper presents the latest developments in ISOCAM data analy­
sis with the Interactive Analysis System for ISOCAM (CIA). 10 The main
use of the system is now to improve the calibration of ISOCAM, the
infrared camera on board the Infrared Space Observatory (ISO) and to
perform its astronomical data processing.
We review the algorithms currently implemented in CIA and present
some examples. We will also outline foreseen changes to accommodate
future improvements for these algorithms.
10 CIA is a joint development by the ESA Astrophysics Division and the ISOCAM Consortium.
The ISOCAM Consortium is led by the ISOCAM PI, C. Cesarsky, Direction des Sciences de
la Matiere, C.E.A., France.
275

276 Ott et al.
1. Introduction
ESA's Infrared Space Observatory (ISO) was successfully launched on November
17th, 1995. 11 ISO is an astronomical, three­axis­stabilized satellite with a 60­cm
diameter primary mirror (Kessler et al. 1996). Its four instruments (a cam­
era, ISOCAM, an imaging photo­polarimeter and two spectrometers) operate at
wavelengths between 2.5­240 microns at temperatures of 2­8 K.
ISOCAM takes images of the sky in the wavelength range 2.5 to 18 microns
(Cesarsky et al. 1996). It features two independent 32 x 32 pixel detectors: the
short­wavelength channel (2.5 to 5.5 microns), and the long­wavelength channel
(4 to 18 microns). A multitude of filters and lenses enable the observer to
perform measurements at di#erent wavelengths, with di#erent fields of view or
with polarizers.
The development of CIA was started in 1994, its main goals being to cal­
ibrate ISOCAM, to provide the means to perform any sort of investigation re­
quested for problem diagnostics, to assess the quality of ISOCAM pipeline data
products, to debug, validate and refine the ISOCAM pipeline and to perform
astronomical data­processing of ISOCAM data. The overall system now repre­
sents an e#ort of 20 man­years and comprises over 1300 IDL and 350 fortran,
C, and C++ modules and 30 MB of calibration data.
At the moment CIA is distributed to experienced users upon approval;
currently it is used at 30 authorized sites. However, this policy will change with
the end of ISO operations in summer 1998. Thereafter CIA V3.0 will be made
generally available for the astronomical community.
2. Steps for ISOCAM Data Processing
At the moment, the following steps for astronomical ISOCAM data processing
are generally performed:
1. data preparation (slicing, generation of CIA prepared data structures)
2. cross­talk correction (for the short­wave detector only)
3. deglitching (removal of cosmic ray hits)
4. dark current subtraction
5. transient correction (compensation for flux­dependent, short timescale vari­
ation of the detector response)
6. flat­fielding
7. averaging
8. configuration dependent processing
(a) raster observations: mosaic generation
(b) CVF observations: spectra selection and display
(c) staring and beam­switch observations: image generation
(d) polarization observations: generation of mosaics for polarizers and
hole
9. interfacing with non­ISO data products
11 ISO is an ESA project with instruments funded by ESA member states (especially the PI coun­
tries: France, Germany, the Netherlands and the United Kingdom) and with the participation
of ISAS and NASA.

Data Analysis with ISOCAM Interactive Analysis System 277
3. Review of Selected Steps for ISOCAM Data Processing
3.1. Deglitching and Transient Correction
CIA contains various algorithms for deglitching and transient correction. Mul­
tiresolution median and temporal median filtering algorithms are most com­
monly used for deglitching. Similarly the most commonly used algorithms for
transient correction are the inversion­method and exponential fitting. The re­
sulting quality depends on the amount of data available. Therefore we will try
in the future to treat a whole revolution instead of single observations.
50 100 150 200 250
10
15
50 100 150 200 250
50 100 150 200 250
Original data (top), deglitched data (middle), both overplotted (bottom)
Deglitching of ISOCAM data with a multiresolution Method
Uncorrected Data
Model
Transient corrected
Data
Transient correction of ISOCAM data by exponential fitting
Figure 1. E#ects of deglitching and transient correction
3.2. Flat­Fielding
Flat­fielding with library­flats and automatic flat­fielding using the raster obser­
vation being analysed are both implemented in CIA. However, the lens wheel
does not always come to exactly the same position. When the wheel position for
the observation di#ers from the wheel position reached when the flat­field was
obtained, this a#ects the quality of the final image. Therefore we hope to im­
plement a correction for this e#ect (lens­wheel jitter) in the flat­field algorithm.
3.3. Dark Current Subtraction
Various algorithms can be used for the dark current subtraction. Currently
implemented are the dark correction with library or user supplied darks (e.g.,
handover darks) as well as a second order dark correction. Studies have shown
that the dark can be better predicted as a function of the observation time or
by scaling with a reference dark. It is planned to implement these new dark
corrections in near future.
3.4. CVF Observations: Spectra Selection and Display
CIA users can play with a 2 dimensional spectrum. From the displayed image
a pixel can be selected : the spectrum of this pixel will be displayed. From the

278 Ott et al.
spectrum a wavelength can be selected and the image will be displayed at this
wavelength.
Figure 2. CVF observations: spectra selection and display
3.5. Interfacing with Non­ISO Data Products
CIA users can overlay a contour plot of one image on a colour display of another.
The two input images can come from di#erent instruments, have di#erent size
and resolution --- the only requirement is that there is astrometry information
associated with each image and that they overlap spatially. The images can be
shifted and annotated.
References
Kessler, M., Steinz, J.A. et al. 1996, A & A, Vol. 315, L27
Cesarsky, C., et al. 1996, A & A, Vol. 315, L32
Delaney, M. ed., ISOCAM Interactive Analysis User's Manual, ESA Document
Ott, S., et al. 1997, ``Design and Implementation of CIA, the ISOCAM Interac­
tive Analysis System'', in ASP Conf. Ser., Vol. 125, Astronomical Data
Analysis Software and Systems VI, ed. Gareth Hunt & H. E. Payne (San
Francisco: ASP), 34
Siebenmorgen, R. et al. ISOCAM Data User's Manual, ESA Document, Refer­
ence SAI/95­221/DC
Starck, J­L., & Murtagh, F., et al. Image Processing and Data Analysis --- The
Multiscale Approach, Cambridge University Press