a monitor of the vertical turbulence distribution

1
a monitor of the vertical turbulence distribution
MASS
Victor Kornilova, Andrei Tokovininb, Olga
Vozyakovaa, Andrei Zaitseva, Nicolai Shatskya,
Serguei Potatina, and Marc Sarazinc
aSternberg Astronomical Institute, Moscow bCTIO,
Chile c ESO, Garching
MASS (Multi-Aperture Scintillation Sensor)
measures light fluxes from a bright single star
in 4 concentric-ring apertures A, B, C, and D
with 1 ms time resolution. For each aperture, a
variance of normalized light flux, scintillation
index, is computed. For each pair of apertures, a
differential scintillation index is computed as
well. These 46 indices with 1 minute
accumulation time are used to restore the
turbulence profile with a vertical resolution of
dh/h 0.5.
Turbulence profile from scintillation indices
Weighting functions the dependence of the 4
normal (A,B,C,D) and 6 differential (AB,AC,)
scintillation indices on the distance to
the turbulent layer
Restoration with 6 fixed layers the resulting
response functions of the layers and their
sum (dashed)
Feeding telescope off-axis elliptic primary, 14
cm diameter. Spherical secondary, equivalent
focal distance 3 m.
Feeding telescope off-axis elliptic primary, 14
cm diameter. Spherical secondary, equivalent
focal distance 3 m.
The instrument
Electronics seven microprocessor modules on
RS-485 common line interfaced to a PC computer.
Software under RT-Linux, the program Turbina
controls MASS through GUI. Features real-time
data reduction, instrument self-tests, automatic
operation. Example of real-time display is shown.

Software under RT-Linux, the program Turbina
controls MASS through Graphical User Interface
and menus. Features real-time data reduction,
instrument self-tests, automatic operation.
Example of real-time display is shown.
Optics the light from telescope is reflected by
the folding mirror 1 and passes through a focal
aperture on the disk 2 (controlled by a stepper
motor). The Fabry lens 4 forms an image of the
telescope pupil on the segmentator 7 with a
de-magnification of 20. The segmentator consists
of 4 concentric mirrors with different tilts, the
diameter of the smallest mirror is 1 mm (2 cm as
projected on the pupil). The 4 reflected beams
fall on the spherical mirrors 3A-3D which
re-image the pupil on the photo-cathodes of the
PMTs A,B,C,D. A dichroic beam-splitter 5 reflects
red light to the viewer (mirror 8, lens 9,
eyepiece 10 or a TV camera 10). The spectral
bandpass of 90 nm centered on 480 nm is defined
by the glass filter 6.
The detector box (length 21 cm) contains
optics, photo-multipliers, and electronics
First results
SCIDAR comparison with MASS at La Silla on July
10-11, 2002. The normalilzation was adjusted
between MASS (full line) and SCIDAR (dash),
SCIDAR was convolved with the MASS vertical
response.
CONCLUSION MASS, a simple and robust instrument
for low-resolution monitoring of turbulence
profile, passed its first tests
successfully. More information and the full text
of this paper at http//www.ctio.noao.edu/atokov
in/profiler
One night July 14-15, 2002 at Cerro Tololo. The
Cn2 profiles restored with fixed-layer method
(top left) and as three floating layers (bottom
left) and the comparison of the full seeing
measured by DIMM with integrated-profile seeing
from MASS which excludes the lower 500m (top).