Transcript Turbulence profiler MASS:

Turbulence profiler MASS:
First tests
and plans
A. Tokovinin
CTIO
http://www.ctio.noao.
edu/~atokovin/profiler
MASS = Multi-Aperture Scintillation
Sensor
• Need for a simple, cheap profile
monitor: single-star profiler
• Presursor: “Scintillometer” of Ochs et al.
• MASS: better hardware, theory and
signal processing (polychromatic
scintillation; photon counting; debiasing)
The principle
Weighting functions
Profile restoration
• Six fixed layers (0.5,1,2,4,8,16 km)
Least-squares solution: Cn2 can be negative…
-> Min. Chi-squared with sign constraint!
• Three “floating” layers: free intensities
and altitudes (6 parameters)
• Direct computing of moments
Simulations: one layer
Simulations: two layers
The instrument • Detector box
(4 PMTs, 1 stepper motor, 7
microprocessors)
• Feeding telescope
(14 cm, off-axis)
• PC + RT Linux
(RS-485 interface)
• Software
• Guiding TV
• Auto-guiding
Real-time data processing
Generalized mode
• Add “virtual propagation” of 0.5 km to
sense low turbulence
• Constraints: <4 arcsec. guiding, good
optics
• Extensive computer simulations
• Tested: seeing worse than DIMM…
Ground layer?
• Conclusion: do not use gen. mode!
One night of data: May 2-3, 2002
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Profile: fixed layers
Profile: floating layers
Comparison with DIMM
Residuals
More profiles… May 20 and 21
A night with good seeing: April 17-18
Comparison with DIMM
Two MASS instruments
Immediate plans (2002)
• Accumulate data for Cerro Tololo
• Move to Cerro Pachon
• SCIDAR calibrations (La Silla, Mauna
Kea)
Instrument development (2003)
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Optimization: smaller outer apertures
Simplify the instrument (no gen-mode)
Simplify data acquisition (no RT Linux)
Couple with DIMM in a single instrument
• Make it all robotic (pointing
!!! )
MASS
+DIMM
Pointing