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Stephen, J. B. & Foschini, L. 2001, in ASP Conf. Ser., Vol. 238, Astronomical Data Analysis Software and Systems X, eds. F. R. Harnden, Jr., F. A. Primini, & H. E. Payne (San Francisco: ASP), 144
PICsIM - the INTEGRAL/IBIS/PICsIT Observation Simulation Tool
for Prototype Software Evaluation
J. B. Stephen and L. Foschini
Istituto TeSRE/CNR, Via P. Gobetti 101, 40129 Bologna, Italy
Abstract:
The INTEGRAL satellite is an observatory-class gamma-ray telescope due
for launch in early 2002. It comprises two main instruments, one
optimised for imaging (IBIS) and the other for spectroscopy (SPI). The
PICsIT telescope is the high energy (150 keV - 10 MeV) plane of the
IBIS imager and consists of 8 individual modules of 512 detection
elements. The modules are arranged in a 4 x 2 pattern, while the
pixels are in a 16 x 32 array. This layout, which includes a dead area
equivalent to one pixel width between each module, together with the
event selection procedure, which (in standard mode) does not allow the
identification of coincidences between separate modules, leads to a
non-uniformity of the background which is significantly different for
single-site events and for multiple energy deposits. Other sources of
background variations range from the separate low energy detector,
situated immediately above the PICsIT plane, to the large mass of the
SPI telescope at a short distance to one side. The algorithms for
performing all the imaging and spectral deconvolution for PICsIT are
currently being produced for delivery to the INTEGRAL Science Data
Centre. In order to maximise the information which may be extracted
from the PICsIT data, we have designed a prototyping environment which
consists of a GUI to a highly structured and modular set of procedures
which allows the easy simulation of observations from the data
collection phase through to the final image production and analysis.
The INTEGRAL high energy gamma-ray satellite consists of two primary
instruments - a high resolution spectrometer (SPI) and a wide spectral
and angular coverage imager (IBIS). IBIS achieves the goal of being
able to create images of the gamma-ray sky over the energy range of
15keV - 10MeV with good angular resolution and large field
of view by utilising two position sensitive detection planes, one
solid state (ISGRI) optimised at lower energies and the other using
scintillator technology (PICsIT) for high energy detection, in
conjunction with a coded aperture mask. There are many possible
sources of disturbance in the imaging process for the PICsIT detector,
ranging from the presence of ISGRI between PICsIT and the coded
aperture, through the modular form of the detection plane construction
to the masses of the other instrumentation nearby.
The PICsIM simulation tool is written entirely using the IDL1 language and runs under
both Windows NT and Linux operating systems. The tool itself provides
only minimum functionality, mainly in the displaying of the images
produced, however it is the interface which allows the developer
straightforward and consistent control of the algorithms he is
creating. This is performed by using a rigid system of data and
algorithm storage which allows the operator to use the tool to
identify the set of procedures available for use at any one time
(e.g., for deconvolution of the image or definition of the accumulation
parameters), and to select the required action. In this way it is also
possible to bypass the data simulation step (which is itself a limited
Monte-Carlo process which does not take into account all physical
processes, and to use the results of a detailed Monte-Carlo simulation
which is also being developed at the TeSRE institute (Malaguti et
al. 2000) merely by placing the event files so produced into the event
file directory and ensuring that a run-ID and associated statistics
file is associated with them. Furthermore, although to date the
various procedures used to define the imaging process are actually IDL
source code, in principle they could also be pre-compiled C or FORTRAN
programs called by the main IDL procedure.
The entire PICsIM simulation, display and evaluation package is
controlled through use of IDL widgets. The top level is the main
control GUI which then activates one of the other second-level GUI’s
on user command. The various commands currently available are detailed
below:
Figure 1:
The GUI to the 'SIMULATE' sub-menu
 |
- SIMULATE This command activates the GUI which allows the
simulation of an observation.
The simulation widget interface is shown in Figure 1.
The source definition procedures (user-defined) are located in the
relevant directory and displayed, as are the instrument characteristic
procedures, which describe how the hardware is functioning, and the
observation strategy (e.g., hexagonal pointing, ‘staring’ etc.) Once
a valid combination is selected a script file is created and the
simulation automatically launched, creating a series of event files,
one for each pointing, with a run-id assigned which is unique for
every observation.
- ACCUMULATE The event files form the input for this GUI which is
shown in Figure 2.
Figure 2:
The GUI to the 'ACCUMULATE' sub-menu
 |
The user can select the files which he wants to accumulate by run-id
(i.e., observation), and further detail may be imposed by selecting
also by sub-pointing. The effective time may also be changed and the
energy channels of the accumulation may be defined by means of
selection of a user written procedure. Details of a particular
observation may be obtained (these are held in the associated
statistics file)
- DECONVOLVE The deconvolution GUI allows the user to select
between various methods of deconvolution (provided as IDL procedures
in the appropriate directory) for the accumulated data files.
- CLEAN This GUI screen shows all the options open (again in
terms of IDL procedures) to the user for cleaning the resulting image,
or filtering the accumulated data files before deconvolution.
- DISPLAY This GUI provides a workspace within which the operator
can display and perform limited analysis on any accumulated
shadowgram, deconvolved and/or cleaned image or sum of images. Figure
3 shows how the operator can display the original detector image, the
corrected shadowgram and the cleaned sky image of a point source.
Figure 3:
The GUI to the 'DISPLAY' sub-menu
 |
The PICsIM simulation environment is a useful tool within which the
algorithms are being developed for use in the final data analysis data
package at the ISDC. Its highly modular form and easy widget-driven
interface allows a rapid evaluation and comparison of new procedures
to be made.
References
Malaguti, G., Ciocca, C. and Di Cocco, G. To be published
in Proceedings of the 4th INTEGRAL workshop, Alicante, Spain,
September 2000
Footnotes
- ... IDL1
-
IDL 5.3, Research Systems Inc., Boulder, Colorado USA
© Copyright 2001 Astronomical Society of the Pacific, 390 Ashton Avenue, San Francisco, California 94112, USA
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