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Marteau, S., Gendron, E., Lacombe, F., Mouillet, D., Lagrange, A.-M., Rousset-Rouvière, L., Rabaud, D., Conan, J.-M., Rousset, G., Zins, G., & Hubin, N. 2000, in ASP Conf. Ser., Vol. 216, Astronomical Data
Analysis Software and Systems IX, eds. N. Manset, C. Veillet, D. Crabtree (San Francisco: ASP), 365
A User-Friendly Way to Optimize Adaptive Optics: NAOS Preparation
Software
S. Marteau, E. Gendron, F. Lacombe
Observatoire de Paris/DESPA, 5 pl Jules Janssen, 92195 Meudon Cedex,
France
D. Mouillet, A.-M. Lagrange
Laboratoire d'Astrophysique de l'Observatoire de Grenoble,
UJF - BP 53, 38041 Grenoble Cedex 9, France
L. Rousset-Rouvière, D. Rabaud, J.-M. Conan, G. Rousset
Office National d'Etudes et de Recherches Aérospatiales, BP
72, 29 av de la Division Leclerc, 92322 Chatillon Cedex, France
G. Zins
SHAKTI, 27 bld Charles Moretti, 13014 Marseille, France
N. Hubin
European Southern Observatory, K. Schwarzchild Str-2, D 85748
Garching, Germany
Abstract:
The concept of NAOS
1Preparation Software (PS) enables any user to optimize the adaptive optics
(AO) system, independently of his/her level of expertise. The required inputs
merely focus on the choice of the astronomical object used to close the AO
loop, while hiding technical parameters of the system to the astronomer's
view. This is achieved by using
a priori knowledge of the instrument to
select the best configuration. The PS also returns an estimation of the
expected performance. For convenient use, the PS is accessible on the World
Wide Web throughout Phases I and II of the preparation.
1. Introduction
The preparation of observations to be carried out with adaptive optics systems
(esp. NAOS) is more complex than with other instruments, for the following
reasons:
- the number of parameters to set is larger than for a simple imager or
even a spectrograph. Furthermore, they concern the algorithm which
is used to optimize the corrected beam and are a priori unfamiliar to
most observers, while critical for the performance. Usually, it is possible to
restrict the number of input parameters by defining observational modes, thus
allocating default values to instrument parameters, leaving only a few degrees
of freedom to the user. In the case of NAOS there are no such modes, because
the inputs may vary in such a range that it is not possible to define a
restricted set of use cases. Indeed, the wavelength of observation for the
science instrument, as well as the characteristics of the AO reference object,
give rise to a very large set of instrument configurations, so that NAOS has
to be tuned for each individual case;
- optimizing the instrumental configuration for a given observation highly
depends on external conditions, such as the reference object used to close the
AO loop, and the turbulence condition in the atmosphere. Furthermore,
assumptions made during the preparation about these issues may have to be
revised when starting the observation (non-predictability of the turbulence,
possible wrong assumptions about the shape or photometry of the reference
object);
- the main scheduling criterion is the achievable performance, in terms of
Strehl ratio, and there is of course not a one-to-one relation between this
criterion and the configuration of the AO system.
This pleads for an advanced user support when the astronomer is to prepare an
observation using NAOS. The aim of the PS is to provide the astronomer with a
unified interface for everything that pertains to the preparation of the
adaptive optics system, from the choice of the reference object to the setting
of the needed template2 parameters. The tool is
to be available during the program handling phase, but will also be requested
during the observation itself, for on-line performance estimation and possible
re-optimization of the AO system configuration. When in Phase I or II of
preparation (see contexts of use in section 3.), the
astronomer will be able to request the PS via a web server.
2. Features of NAOS PS
Considering the remarks made in the previous section, the design of the PS has
to take into account and implement the following features:
- Graphical User Interface:
- available in two forms. During Phases I and
II, the PS will be accessible on the Internet via a regular web browser. The
on-line version of the PS will have a standard, VLT-compliant interface.
- Interface to star catalogues:
- the user will be able to request remote
star catalogues directly from the interface of the PS. The request to the
catalogues will take into account information about the science object.
- Simulation parameters and user constraints:
- the atmospheric conditions
used for the internal simulation of the AO system will be configurable by the
user. It will also be possible to freeze some instrumental
parameters of the configuration of NAOS, to ensure that they will not be
modified by a possible on-line re-optimization during the observation. For
example, the astronomer's knowledge of the scientific issues of the
observation may lead him to impose a specific wavefront sensor, either the
visible or the infrared one.
- Results of the simulation:
- the PS returns an optimized set of NAOS
parameters for the observation specified by the user. The
expected image quality is also returned in the form of the PSF and its
derivatives.
- Interface with the VLT P2PP tool:
- ESO provides a
dedicated preparation tool for Phase II (aka P2PP), which enables to build
Observation Blocks that represent the observation program.
It will be possible for the user to transfer the results obtained with the PS
back into the P2PP tool.
3. Contexts of Use
As said above, the PS will be available to the astronomers
from the program proposal to the observation. This implies that several
copies of the PS will be available, depending on the context of use.
During Phase I of the preparation, the PS is available for ``feasibility
analysis''. Only a minimum set of inputs is required: for example, one can ask
for a performance estimation, only specifying a F1 star with 
, without
having to choose an actual object in a catalogue. Phase II uses the same tool
but this time it requires detailed inputs, as the result of the PS has to be
used to build some Observation Blocks. In both cases, the software is accessed
through Internet.
During the observation, the PS may also requested for performance estimation,
or for an optimization of an instrumental configuration. This time, the PS is
a part of the NAOS operational software, and relies on real-time information
for atmospheric conditions and characteristics of reference objects. The
request may come from the user, the NAOS Observation Software, or the VLT
Scheduler.
4. User Interface
Figure 1 shows an early mock-up of the interface.
One may notice that the configuration of the AO system only takes a small part
of the panel, while a good third of it is devoted to the choice of the
astronomical object which will be used to close the AO loop during the
observation.
Figure 1:
Early design of the NAOS Preparation Software GUI.
 |
Generally speaking, one tries to emphasize what is relevant to
the astronomer, while leaving out the setting of technical parameters to the
software. When observing, the GUI is only called if interaction with the user
is absolutely necessary, e.g. when the reference object is too peculiar for
NAOS to find an optimal configuration.
5. Internal Conception
To achieve the optimization of NAOS configuration and compute the
corresponding, expected performance (in terms of image quality), the knowledge
of the instrument is first used to choose the best values for the numerous
parameters of the system. This task is devoted to the Configuration
Optimizer, which uses a set of configurable rules that are parsed according
to the user inputs, and possible constraints about the availibility of
hardware resources. The rules are written with a simple syntax, and can be
easily modified so as to tune the behaviour of the system. A syntactic
analyzer based on lex and yacc tools is first used to translate
these rules into core objects that are understandable by the Configuration
Optimizer. The output of this sorting phase is a set of suitable NAOS
configurations, which should be as small as possible. Indeed, these
configurations are then sent to the Performance Estimator, which builds
an internal, physical model of the instrument and of the atmosphere. It
outputs an estimation of the point-spread function, as seen with the AO system
in closed loop. The Configuration Optimizer can then make the final decision
and choose the best-suited settings for NAOS. Derivated quantities such as
encircled energy, FWHM and Strehl ratio are also sent back to the user. The
PSF is calculated on-axis, i.e. for the reference object, but an option is
available to the user, that gives an estimation of the PSF in the direction of
the science object by taking into account the anisoplanetism angle.
6. Conclusion and Perspective
The final design of NAOS Preparation Software has been accepted by ESO in
January 1999. Software development will occur in the first half of 2000, so
that the PS should be completed by the end of July. It will thus be available
for observations to be carried out from the beginning of 2001.
Footnotes
- ... NAOS1
- Nasmyth Adaptive Optics System for the VLT.
- ... template2
- Templates are high-level observation sequences
defined for all VLT instruments. Template calls are usually generated through
the P2PP tool (cf. section 2.)
© Copyright 2000 Astronomical Society of the Pacific, 390 Ashton Avenue, San Francisco, California 94112, USA
Next: QuickLook Data Reduction Pipeline - Keck Adaptive Optics Real Time Data Reduction Software
Up: Adaptive and Active Optics
Previous: GBT Active Optics Systems and Techniques
Table of Contents -
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PS reprint -
adass@cfht.hawaii.edu