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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.
News on the ISOPHOT Interactive Analysis PIA
C. Gabriel
ISO Science Operations Centre, Astrophysics Division, Space Science
Department of ESA, Villafranca, P.O. Box 50727, 28080 Madrid,
Spain, Email: cgabriel@iso.vilspa.esa.es
J. Acosta­Pulido 1
Max­Planck­Institut f˜ur Astronomie, Heidelberg, Germany
I. Heinrichsen 1
Max­Planck­Institut f˜ur Kernphysik, Heidelberg, Germany
Abstract. The ISOPHOT Interactive Analysis system, a calibration
and scientific analysis tool for the ISOPHOT instrument on board ESA's
Infrared Space Observatory (ISO), has been further developed while ISO
is in operation. In this paper we describe some of the improvements
achieved in the last few months in the areas of scientific analysis capabil­
ities, documentation and in related services to the astronomical commu­
nity.
1. Introduction
The ISOPHOT Interactive Analysis (PIA) is an IDL based software tool de­
veloped for calibration and scientific analysis of data from ISOPHOT (Lemke
et al. 1996), one of the instruments on board ISO (Kessler et al. 1996). The
general features of PIA, its use as a calibration tool and the built­in mapping
capabilities were presented at the ADASS VI conference (Gabriel et al. 1997a,
1997b and 1997c).
The development of PIA, up to the initial phase of the mission, was de­
scribed by Gabriel et al. (1996). After 2 years of ISO operations considerable
experience has been gained in the use of PIA, which has led to several new
features in the package. This experience has been achieved by the ISOPHOT
Instrument Dedicated Team in its tasks which include calibration, instrument
performance checking and the refinement of analysis techniques, and also by a
large number of ISOPHOT observers in more than 100 astronomical institutes
all over the world.
1 at ISO Science Operations Centre, Astrophysics Division, ESA­SSD, Villafranca, P.O. Box
50727, 28080 Madrid, Spain
165

166 Gabriel, Acosta­Pulido and Heinrichsen
PIA has been widely distributed since July 1996 to all astronomers wishing
to use it for ISOPHOT data reduction and analysis. The feedback from the
di#erent users is reflected not only in the extension of the analysis capabilities
but also in a more friendly graphical interface, better documentation, and easier
installation.
2. PIA Improvements
In the last year of the ISO mission the PIA capabilities have been continu­
ously enhanced. All the areas of data processing routines, automatic analysis
sequences, graphical user interface, calibration menus, configuration, distribu­
tion and information have been a#ected by changes. In this paper we describe
the developments in three sections:
. transients modeling implementation, showing changes in the areas of data
processing routines and GUI,
. documentation improvements, for the areas of information and mainte­
nance, and
. system testing procedures implementation, for the areas of reliability and
support.
2.1. Transients Modeling
ISOPHOT detectors have long stabilization times, which is a known feature af­
fecting IR detectors (Si:Ga, Si:B and Ge:Ga) operating at very low backgrounds.
The measurement times are usually shorter than the required stabilization, and
this represents a major impediment to the calibration of the instrument and
to obtaining a good signal to noise ratio. The transient behaviour depends on
several parameters including the flux level to be measured (varying over several
orders of magnitude), the previous flux history (flux down or flux up with all
levels of di#erence) and the detector type of the sub­system used.
The approach followed is to use physical and empirical models to fit the
data and predict the final flux which would have been obtained for a fixed sky
point if measured for su#ciently long. Depending on the sub­system detector
di#erent functions and model parameters are proposed:
. physical models for silicon based detectors (Schubert et al. 1995; Fouks et
al. 1996)
. empirical models for Ga:Ge detectors (Fukiwara et al. 1995; Church et al.
1996)
The dependencies on flux level and history are reflected in the starting param­
eters of the di#erent models (which can be fixed for the fitting procedure).
Fitting of a signal distribution corresponding to the measurement of a sky
position begins with the determination of the starting parameters corresponding
to the type of data and function to be used. The minimization of the Chi­squared

News on the ISOPHOT Interactive Analysis PIA 167
or least squares fitting is done first with a downhill simplex method 2 for a first
approximation varying the parameters. The parameters with the values thus
obtained are then used as starting parameters for a second fit using a Gradient­
expansion algorithm for a least squares fit to a non­linear function 3 .
The graphical user interface includes the possibility of: a) choosing among
the di#erent functions with the corresponding parameter initialisations, b) gen­
eral parameters for the analysis can be set, such as selection criteria, tolerance
level for the fit, weighting method to be used, c) specific function parameters
can be reset after initialisation, varied or fixed, tolerance limits can be set.
All the start parameters can be tested and adjusted before analysing a full
measurement using portions of the data. After full analysis PIA also provides the
opportunity of reassessing the results with partial refitting, using for example,
the Chi­squared or the adjusted parameter distributions of all the fitted data
for evaluation. This makes the analysis of large data sets very e#cient, while
permitting fast and deep data manipulation.
2.2. Documentation
We have created the PIA homepage 4 for several reasons:
. to give users faster access to PIA,
. to create an e#cient feedback route from the astronomical community to
the PIA developers,
. to provide the community with better maintenance and service.
The PIA homepage contains the latest version of PIA together with the release
notes and the PIA user's manual both in its HTML and PostScript versions.
Publications on PIA can also be seen or retrieved and frequently asked questions
and answers are listed. A mailbox is attached to receive bug reports, comments,
etc. Especially useful for advanced PIA users are the listings of routine headers,
which can be used by external calls and allow re­use of the PIA routines.
2.3. System Testing Procedures
Procedures for testing PIA are applied prior to every new release (main versions
are released annually, while sub­versions are every two to three months). The
automatic sequences built within PIA are used for running over a huge repre­
sentative dataset containing all major ISOPHOT observing modes with good
reference data. The sequences run through all the data reduction steps perform­
ing all the default corrections and saving data in the di#erent formats at all
reduction levels. These procedures can not only check the reliability of the new
version but also are used for testing the level of calibration accuracy for a new
sub­version and/or new calibration files. These tests are also used for checking
the reliability of the software under di#erent IDL versions and di#erent machine
architectures.
2 as given by the IDL function AMOEBA.
3 we use a slightly changed version of the IDL routine CURFIT
4 http://isowww.estec.esa.nl/manuals/PHT/pia/

168 Gabriel, Acosta­Pulido and Heinrichsen
3. Outlook
The end of the ISO mission, due to Helium boil­o#, is foreseen for April 1998.
PIA will be further developed during the ``Post­operational phase'', starting then
and lasting at least 3.5 years. The huge amount of ISOPHOT data collected, the
excellence of their scientific content, the quality of the instrument and the further
consolidation of its calibration result in scientific work for a wide community
for years to come. One of the reasons for this is that the ISO archive will
be open to everyone for archive research once the proprietary rights expire.
PIA plays a major r“ole as the tool for data reduction and scientific analysis
of ISOPHOT data, and new requirements are continuously arising from the
analysis experience of its users. Concrete planning for further PIA development
includes the provision of imaging enhancement techniques as well as coherent
maps co­addition, polarimetry analysis, time and orbit dependent calibration,
etc..
References
Church, S. et al. 1996, Applied Optics, Vol. 35, No. 10, 1597
Fouks, B., & Schubert, J. 1995, Proc. SPIE 2475, 487
Fukiwara, M., Hiromoto, N., & Araki, K. 1995, Proc. SPIE 2552, 421
Gabriel, C., Acosta­Pulido, J., Heinrichsen, I., Morris, H., Skaley, D., & Tai,
W. M. 1996, ``Development and capabilities of the ISOPHOT Interac­
tive Analysis (PIA), a package for calibration and astronomical analysis'',
Proc. of the 5th International Workshop on ``Data Analysis in Astron­
omy'', Erice, in press
Gabriel, C., Acosta­Pulido, J., Heinrichsen, I., Morris, H., Skaley, D., & Tai,
W. M. 1997a, ``The ISOPHOT Interactive Analysis PIA, a Calibration
and Scientific Analysis Tool'', in ASP Conf. Ser., Vol. 125, Astronomical
Data Analysis Software and Systems VI, ed. Gareth Hunt & H. E. Payne
(San Francisco: ASP), 108
Gabriel, C., Acosta­Pulido, J., Kinkel, U., Klaas, U., & Schulz, B. 1997b,
``Calibration with the ISOPHOT Interactive Analysis (PIA)'', in ASP
Conf. Ser., Vol. 125, Astronomical Data Analysis Software and Systems
VI, ed. Gareth Hunt & H. E. Payne (San Francisco: ASP), 112
Gabriel, C., Heinrichsen, I., Skaley, D., & Tai, W. M. 1997c, ``Mapping Using
the ISOPHOT Interactive Analysis (PIA)'', in ASP Conf. Ser., Vol. 125,
Astronomical Data Analysis Software and Systems VI, ed. Gareth Hunt
& H. E. Payne (San Francisco: ASP), 116
Kessler, M. et al. 1996, A&A, 315, L27­L31
Lemke, D. et al. 1996, A&A, 315, L64­L70
Schubert, J., et al. 1995, Proc. SPIE 2253, 461