Optical Turbulence Database                                                   

The Database is part of the ForOT activity and aims to be a tool of investigation for us and a mean to keep the Large Binocular Telescope (LBT) Consortium informed about progress achieved on turbulence characterization above Mt. Graham (site of LBT). The web page is conceived to be in constant evolution. The number of measurements related to the different Astronomical Sites are not homogeneous and not equivalent from a statistical point of view. This means that statistic estimators (cumulative distributions, median and means values) are a function of sample of measurements emploied. It is our intention to try to actualize figure of merit up-dating results using data-set related to forthcoming site testing campaigns.

To respect the data usage policies of colleagues who provided us measurements obtained so far in different astronomical sites this web page is, at present time,  password protected. On the table are indicated links either to published papers or analysis unique to these pages.

Content of this page:

Tabulated summary

Site of the Measurements Instrument Type* Sampling Statistics
Analysis Notes
external links internal links
Mt. Graham VATT:
32.7 N, 109.87 W; H=3200
HVRGS 851 / 30 sec / 1 eqv.nghts Egner & Masciadri, (2007), PASP
& ForOT Activity

GS on the Lennon telescope (VATT) is 35 meters below and 250 meters laterally from the LBT primary mirrors.
GS 10522 / 50 sec / 8 eqv.nghts Egner, Masciadri, McKenna, (2007), PASP (first 16 nights)
& ForOT Activity

free-seeing comparison
75 06 S, 123 21 E; H=3260 m
SODAR-MASS 1701 / 65 sec / 3 eqv.nghts Lawrence et al.(2004) Nature Kenyon et al.(2006) PASP
The SODAR data provided are only one J(h_GL) value matching each MASS measurement.
Cerro Pachon:
30 24 S, 70 44 W,;
H= 2738 m
MASS 40630 / 70 sec / 64 eqv.nghts Tokovinin and Travouillon (2006) MNRAS
(only calibrated measurements)
seasonal trends There are DIMM measurements from a combined MASS-DIMM instrument, but they are not provided. Of those available, the newer data are from a 6 meter tower, older data are from a 1.5 meter tripod.
Cerro Tololo:
30 09 S, 70 48 W;
H=2215 meters
MASS 129153 / 70 sec / 206 eqv.nghts
Mauna Kea:
19 49 N, 155 28 W; H=4200 M
MASS 3819 / 65 sec / 6 eqv.nghts  Tokovinin et al.(2005) PASP
(4 nights)

Generalized MASS using the U of Hawaii 24 inch telescope. 1369 of these measurements are strongly affected by errors from tracking and saturation of the signal due to strong free-seeing.
DIMM ~3819 /

0.25 meter Meade on the coude roof of the U of Hawaii 88 inch telescope. There was another DIMM instrument running simultaneously on a tripod outside the U of Hawaii 24 inch, but it is contaminated by too much surface turbulence.
GS 6530 /

Generalized SCIDAR with the U of Hawaii 88 inch telescope
Cerro Paranal
70 24' W, 24 37' S;
H=2400 m


Definition of terms

GS = G-SCIDAR = Generalized Scintillation Detection And Ranging
HVRGS = High Vertical Resolution GS
MASS = Multiple Aperture Scintillation Sensor
DIMM = Dual Image Motion Monitor
SODAR = Sonic Detection And Ranging
Number of Samples / typical sample interval (seconds) / total length of intervals shorter than 180 sec
eqv.nghts = equivalent number of nights is the length of time in units of 12 hours.

Definition of astro-climatic parameters

In the following plot we provide cumulative histograms of isoplanatic angle and seeing from the free atmosphere, defined here to be the above 700 meters from the site. Isoplanatic angle and seeing are common astro-climatic parameters defined as
Unless stated otherwise the wavelength λ is 0.5 microns in these pages. The Cn2 moment μ with subscript m is computed from N layers of Cn2 integrals Ji
The hi is vertical height above the site of the ith Cn2 integral. Ideally we would measure an arbitrarily large number of Cn2 integrals. Each method of OT measurment has its own limitations that limit the number N. In general the layer measurements can be modeled with
where Wi is some weighting function for the ith layer. The height hi is generally defined to be at the peak of Wi.

Cumulative histograms

The plot below shows cumulative histograms of the above astro-climatic parameters calculated for five of the astronomic sites in the above table. These pictures are for internal use ONLY.

Fig. 1 - Caption:  Raw data set for the astronomical sites are related to:

Mt. Graham: All nights (37 at present)
Mauna Kea:
Tokovinin et al. 2005, PASP, 117, 395
Dome C: Lawrence et al., 2004, Nature, 431, 278
Cerrto Tololo and Cerro Pachon:

Mount Graham: 20/05/2005 - 29/10/2007 (SCIDAR, 100 hours)
Dome C: 24/03/2004 - 05/04/2004 (MASS, 30 hours)
Cerro Pachon: 09/01/2003 - 20/11/2006 (MASS, 760 hours)
Cerro Tololo: 19/03/2002 - 04/12/2006 (MASS, 2400 hours)
Mauna Kea: 19/10/2002 - 24/10/2002 (MASS, 70 hours)

WARNING: We invite the reader to not retrieve fast and wrong conclusions on the quality of the different sites. As it is known, the cumulative distributions are quite sensitive to the sample emploied. Here down the same cumulative distribution of Fig. 1 is calculated using only the first 16 nights of Mt. Graham (instead of 32 nights as Fig. 1). The reader can note that the statistic of the distribution changed in a not negligible way.

Fig. 2 - Caption: Same as Fig.1 but with a different statistic sample of nights

Data are treated by Jeff Stoesz
E.Masciadri, 1/2008