OF TECHNIQUES FOR OPTICAL
developement of new techniques/instruments for the measurements of the
optical turbulence is certainly a crucial element in this research
field and certainly useful to achieve the ForOT scientific goals. Since
the beginning of the ForoT project, the team has been concerned on two
(1) the exploitation of a new
method/technique that has been proposed very recently by Egner &
Masciadri (2007) and
called High Vertical Resolution Generalized Scidar (HVR-GS)
(2) a joint project carried
out in collaboration with the J. Storey team (University of New South Wales,
Sydney, Australia), A. Pellegrini team (ENEA/PNRA,
Roma, Italy) and the Italian Air
Force - Meteo Experimental Section, (Vigna di Valle, Roma,
Italy) aiming at developing microthermal sensors to be mounted on
balloons for CN2 measurements above Antarctica.
J. Storey's team lead the development of
these sensors. This work has
been done in the context of the project ForOT@DC (PI: E. Masciadri) approved
by the Concordia Station Steering Committee of Dome C and aiming
at performing an intense site testing campaign with different vertical
profilers running simultaneously for the validation of the numerical
technique for optical turbulence prediction above Antarctica.
(1) HVR-GS (High Vertical Resolution - Generalized
The High Vertical Resolution
Generalized Scidar (HVR-GS) is a technique
recently proposed by Egner &
Masciadri (2007). The Generalized
Scidar instrument is used in a particular way to provide CN2
the first kilometer with a very high vertical resolution (~25-30 m).
The HVR-GS technique has been exploited using data from intense site
testing campaigns carried out at Mt. Graham whose results are
summarized in Masciadri et
The HVR-GS technique is based on the simultaneous acquisition of auto
cross-correlation of scintillation maps produced on the pupil of the
telescope by binary stars with a
separation θ of the order of 30"-35"; m1, m2 ≤ 5.8 mag;
≤ 1.5 mag..
: The figure shows a set of triplets obtained
cross-correlation of scintillation maps taken at the Vatican Advanced
Technology Telescope observing β Cyg (θ = 35") with time lag of
50 msec. Beside each triplet is indicated the height of the
correspondent turbulent layer and its wind speed.
Fig2: (from Masciadri
et al. 2010): Optical turbulence vertical
distribution structure obtained with the HVR-GS technique and the
richest available sample of nights (43 nights) above Mt. Graham. Mean CN2
calculated above Mt. Graham from the
corresponding 45-55 % of the J cumulative distribution. J is the integral of
the CN2 on a thickness equal to Δ h. The sample
composed of 43 nights. The dome contribution
excluded. Thin layers are well visible in the first kilometer
SENSORS FOR CN2
On 1-4 July 2008 a
site testing campaign has been carried out at Vigna del Valle, Rome,
(Italy) to validate the experimental set up for measuring the CT2
and CN2 vertical profiles in the whole 20 km
above the ground.
Fig. 1: Meteorological station
the Italian Air
Force - Meteo Experimental Section at Vigna del Valle, Rome, Italy
where experiments have been carried out.
Fig.2: Top-left: The electronic board for the microthermal sensors. Top-right: The Digicora Station for the reception of the signal from
the Vaisala meteo sonde. Bottom-left: D. Luon-Van
and J. Storey with the meteo Vaisala sonde. On the top of the sonde it
is placed a very light bar (1 m long) with two thermocouples at the
extremities (the white circles indicate the position of the
microthermal sensors). Bottom-right: The balloon in the hangar is ready for the lunch.
Fig. 3: Top-left: Preparation of the
radiosonde battery. Top-right:
People are ready to launch the balloon. Bottom-left: Test done during the daytime. The balloon is on sky and,
some tens of meters behind is visible the radiosonde where the
microthermal sensors are placed. Bottom-right: Test done during the nighttime. J. Storey, E. Masciadri and
a member of the Italian Air Force team are looking at the
balloon flying away
just after the launch.
Fig.4: Example of the CT2 (left panel) and CN2
extended on the 20 km
and retrieved from the
launch of a balloon. The
vertical resolution of ~ 6 m permits to put in evidence several thin
layers all along the 20 km. CN2 values are as
small as 10-19
and this indicates that the sensitivity of the microthermal sensors is
reasonably good as expected by such a kind of sensors for measurements
above the Internal Antarctic Plateau (raw measurements from: D.
Acknowledgments: This work is
funded by the Marie Curie Excellence Grant ForOT - MEXT-CT-2005-023878.
For the experiment of microthermal sensors for CN2
funded the thermocouples purchase.