.
The new performances are to provide the temporal evolution of turbulence profiles in real time with and without dome seeing contribution, and the remote control of all the instrument. The design has been also adapted to the characteristics of the AT (1.8m) in which it has been installed (Fig. 3, 4, 5).
From now on, ESO will operate the instrument and take care of the measurements; the IAC SCIDAR team will continue colaborating with ESO, within the FP6 site Characterisation WP in the data validation and analysis.
SCIDAR has proved to be the most efficient technique to obtain the
optical vertical structure of the atmospheric turbulence measured
from ground level. However, the common procedure of obtaining
the data, as well as its 'a posteriori' treatment, requires
a huge number of highly qualified human resources. A systematic
monitoring programme becomes really onerous. Consequently, the
development of a full automatically controlled SCIDAR device
seems to be evidently justified.
.
REQUIREMENTS
AND SPECIFICATIONS
The
control mechanisms are fixed: a) by the positioning of the
camera in the conjugated plane of detection and the optical
axis, and b) by the rotation of that plane to orient the separation
of the binary star with the rows of pixel of the detector.
a)
The camera is lodged in two devices that give the movement
in XY, which allows correcting small displacements in the
observation plane produced by flexion. Movement Z (optical
axis) is provided by a long electronic-rail that, besides
to position the camera in the observation plane, facilitates
the procedure of focusing of the instrument, since it permits
to verify easily with a single star the state of collimation
of the beam. The maximum range in XY is 25 mm and in Z it
is of 300 mm.
b)
The rotation of the plane is generated turning the complete
instrument with respect to the telescope. The range of total
turn is 270º, and it is transmitted through a crown wheel. Another
complementary mechanism is an iris, placed in the focal plane
(see the scheme of Figure 2), also electronically controlled.
A
specific software package for the control of the devices,
acquisition and data pre-processing has been developed. On
the other hand, one user-friendly interface based on windows
allows handling all the controls (Fig. 6, 7). In this version, an essential enhancement is the output of the turbulence profiles in real time (Fig. 8).
CONCLUSIONS
The
high cost of resources that entails the monitoring of the
turbulence with quite height resolution justifies the development
of an instrument that diminishes these constraints. The plan
of a long campaign of measurements of the vertical structure
of the turbulence in the Roque of Muchachos and Teide observatories
has encouraged to us to built an instrument with high performances
and minimal operational efforts. With this experience, we have been able to develop a new version for Paranal, within the European Extremely Large Telescope Design Study (Contract 011863 with the European Commission). Cute-SCIDAR is a full automatically
controlled instrument. This means a complete automation of
both displacement of optical elements and rotation of the
instrument itself. These movements are controlled by a user-friendly
interface. Moreover, this custom-made software packet performs
fast data acquisition and processing, which can give the turbulence profiles in real time, with and without dome seeing. As a consequence, alignment
and observation procedures reduce to easy handling and without
the effort operating in the dome. These performances lead to a high temporal
profit during the observation campaign as well as an essential tool in order to optimize the efficiency of the AO/MCAO systems.
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