Table of Contents -- Index -- PS reprint -- PDF reprint

Astronomical Data Analysis Software and Systems VII
ASP Conference Series, Vol. 145, 1998
Editors: R. Albrecht, R. N. Hook and H. A. Bushouse

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. Acosta-Pulido¹
Max-Planck-Institut für Astronomie, Heidelberg, Germany

I. Heinrichsen¹
Max-Planck-Institut für Kernphysik, Heidelberg, Germany

¹at ISO Science Operations Centre, Astrophysics Division, ESA-SSD, Villafranca, P.O. Box 50727, 28080 Madrid, Spain

 

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 capabilities, documentation and in related services to the astronomical community.

             

1. Introduction

The ISOPHOT Interactive Analysis (PIA) is an IDL based software tool developed 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 built-in 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 described 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.

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 different 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 continuously enhanced. All the areas of data processing routines, automatic analysis sequences, graphical user interface, calibration menus, configuration, distribution and information have been affected 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 maintenance, 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 affecting 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 difference) and the detector type of the sub-system 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 sufficiently long. Depending on the sub-system detector different 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 parameters of the different 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 Chi-squared or least squares fitting is done first with a downhill simplex method 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 non-linear function.

The graphical user interface includes the possibility of: a) choosing among the different functions with the corresponding parameter initialisations, b) general 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 Chi-squared or the adjusted parameter distributions of all the fitted data for evaluation. This makes the analysis of large data sets very efficient, while permitting fast and deep data manipulation.

2.2. Documentation

We have created the PIA homepage for several reasons:

• to give users faster access to PIA,
• to create an efficient 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 re-use 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 sub-versions are every two to three months). The automatic sequences built within PIA are used for running over a huge representative dataset containing all major ISOPHOT observing modes with good reference data. The sequences run through all the data reduction steps performing all the default corrections and saving data in the different 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 sub-version and/or new calibration files. These tests are also used for checking the reliability of the software under different IDL versions and different machine architectures.

3. Outlook

The end of the ISO mission, due to Helium boil-off, is foreseen for April 1998. PIA will be further developed during the ``Post-operational 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 rôle 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 co-addition, 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., Acosta-Pulido, J., Heinrichsen, I., Morris, H., Skaley, D., & Tai, W. M. 1996, ``Development and capabilities of the ISOPHOT Interactive Analysis (PIA), a package for calibration and astronomical analysis", Proc. of the 5th International Workshop on ``Data Analysis in Astronomy", Erice, in press

Gabriel, C., Acosta-Pulido, J., Heinrichsen, I., Morris, H., Skaley, D., & Tai, W. M. 1997a, ``The ISOPHOT Interactive Analysis PIA, a Calibration and Scientific Analysis Tool", in Astronomical Data Analysis Software and Systems VI, ASP Conf. Ser., Vol. 125, eds. Gareth Hunt and H. E. Payne (San Francisco, ASP), 108

Gabriel, C., Acosta-Pulido, J., Kinkel, U., Klaas, U., & Schulz, B. 1997b, ``Calibration with the ISOPHOT Interactive Analysis (PIA)", in Astronomical Data Analysis Software and Systems VI, ASP Conf. Ser., Vol. 125, eds. Gareth Hunt and 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 Astronomical Data Analysis Software and Systems VI, ASP Conf. Ser., Vol. 125, eds. Gareth Hunt and H. E. Payne (San Francisco, ASP), 116

Kessler, M. et al. 1996, A&A, 315, L27-L31

Lemke, D. et al. 1996, A&A, 315, L64-L70

Schubert, J., et al. 1995, Proc. SPIE 2253, 461

Footnotes

...method

as given by the IDL function AMOEBA.

...function

we use a slightly changed version of the IDL routine CURFIT

© Copyright 1998 Astronomical Society of the Pacific, 390 Ashton Avenue, San Francisco, California 94112, USA